5. Types natifs

Les sections suivantes décrivent les types standards intégrés à l’interpréteur.

Note

Historically (until release 2.2), Python’s built-in types have differed from user-defined types because it was not possible to use the built-in types as the basis for object-oriented inheritance. This limitation no longer exists.

The principal built-in types are numerics, sequences, mappings, files, classes, instances and exceptions.

Some operations are supported by several object types; in particular, practically all objects can be compared, tested for truth value, and converted to a string (with the repr() function or the slightly different str() function). The latter function is implicitly used when an object is written by the print() function.

5.1. Valeurs booléennes

Tout objet peut être testé typiquement dans une condition if ou while ou comme opérande des opérations booléennes ci-dessous. Les valeurs suivantes sont considérées comme fausses :

  • None

  • False

  • zero of any numeric type, for example, 0, 0L, 0.0, 0j.

  • toute séquence vide, par exemple, '', (), [].

  • toute dictionnaire vide, par exemple, {}.

  • instances of user-defined classes, if the class defines a __nonzero__() or __len__() method, when that method returns the integer zero or bool value False. [1]

Toutes les autres valeurs sont considérées comme vraies — donc des objets de beaucoup de types sont toujours vrais.

Les opérations et fonctions natives dont le résultat est booléen donnent toujours 0 ou False pour faux et 1 ou True pour vrai, sauf indication contraire. (Exception importante : les opérations booléennes or et and renvoient toujours l’une de leurs opérandes.)

5.2. Opérations booléennes — and, or, not

Ce sont les opérations booléennes, classées par priorité ascendante :

Opération

Résultat

Notes
x or y

si x est faux, alors y, sinon x

(1)
x and y

si x est faux, alors x, sinon y

(2)
not x

si x est faux, alors True, sinon False

(3)

Notes :

  1. Ceci est un opérateur court-circuit, il évalue seulement le deuxième argument si le premier est False.

  2. Ceci est un opérateur court-circuit, il évalue seulement le deuxième argument si le premier est True.

  3. not a une priorité inférieure à celle des opérateurs non-booléens, donc not a == b est interprété comme not (a == b) et a == not b est une erreur de syntaxe.

5.3. Comparaisons

Comparison operations are supported by all objects. They all have the same priority (which is higher than that of the Boolean operations). Comparisons can be chained arbitrarily; for example, x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

Ce tableau résume les opérations de comparaison :

Opération

Signification

Notes
<

strictement inférieur

 
<=

inférieur ou égal

 
>

strictement supérieur

 
>=

supérieur ou égal

 
==

égal

 
!=

différent

(1)
is

identité d’objet

 
is not

contraire de l’identité d’objet

 

Notes :

  1. != can also be written <>, but this is an obsolete usage kept for backwards compatibility only. New code should always use !=.

Objects of different types, except different numeric types and different string types, never compare equal; such objects are ordered consistently but arbitrarily (so that sorting a heterogeneous array yields a consistent result). Furthermore, some types (for example, file objects) support only a degenerate notion of comparison where any two objects of that type are unequal. Again, such objects are ordered arbitrarily but consistently. The <, <=, > and >= operators will raise a TypeError exception when any operand is a complex number.

Non-identical instances of a class normally compare as non-equal unless the class defines the __eq__() method or the __cmp__() method.

Instances of a class cannot be ordered with respect to other instances of the same class, or other types of object, unless the class defines either enough of the rich comparison methods (__lt__(), __le__(), __gt__(), and __ge__()) or the __cmp__() method.

CPython implementation detail: Objects of different types except numbers are ordered by their type names; objects of the same types that don’t support proper comparison are ordered by their address.

Two more operations with the same syntactic priority, in and not in, are supported only by sequence types (below).

5.4. Numeric Types — int, float, long, complex

There are four distinct numeric types: plain integers, long integers, floating point numbers, and complex numbers. In addition, Booleans are a subtype of plain integers. Plain integers (also just called integers) are implemented using long in C, which gives them at least 32 bits of precision (sys.maxint is always set to the maximum plain integer value for the current platform, the minimum value is -sys.maxint - 1). Long integers have unlimited precision. Floating point numbers are usually implemented using double in C; information about the precision and internal representation of floating point numbers for the machine on which your program is running is available in sys.float_info. Complex numbers have a real and imaginary part, which are each a floating point number. To extract these parts from a complex number z, use z.real and z.imag. (The standard library includes additional numeric types, fractions that hold rationals, and decimal that hold floating-point numbers with user-definable precision.)

Numbers are created by numeric literals or as the result of built-in functions and operators. Unadorned integer literals (including binary, hex, and octal numbers) yield plain integers unless the value they denote is too large to be represented as a plain integer, in which case they yield a long integer. Integer literals with an 'L' or 'l' suffix yield long integers ('L' is preferred because 1l looks too much like eleven!). Numeric literals containing a decimal point or an exponent sign yield floating point numbers. Appending 'j' or 'J' to a numeric literal yields a complex number with a zero real part. A complex numeric literal is the sum of a real and an imaginary part.

Python fully supports mixed arithmetic: when a binary arithmetic operator has operands of different numeric types, the operand with the “narrower” type is widened to that of the other, where plain integer is narrower than long integer is narrower than floating point is narrower than complex. Comparisons between numbers of mixed type use the same rule. [2] The constructors int(), long(), float(), and complex() can be used to produce numbers of a specific type.

All built-in numeric types support the following operations. See The power operator and later sections for the operators’ priorities.

Opération

Résultat

Notes
x + y

somme de x et y

 
x - y

différence de x et y

 
x * y

produit de x et y

 
x / y

quotient de x et y

(1)
x // y (floored) quotient of x and y (4)(5)
x % y

reste de x / y

(4)
-x

négatif de x

 
+x

x inchangé

 
abs(x)

valeur absolue de x

(3)
int(x)

x converti en nombre entier

(2)
long(x) x converted to long integer (2)
float(x)

x converti en nombre à virgule flottante

(6)
complex(re,im)

un nombre complexe avec re pour partie réelle et im pour partie imaginaire. im vaut zéro par défaut.

 
c.conjugate() conjugate of the complex number c. (Identity on real numbers)  
divmod(x, y)

la paire (x // y, x % y)

(3)(4)
pow(x, y)

x à la puissance y

(3)(7)
x ** y

x à la puissance y

(7)

Notes :

  1. For (plain or long) integer division, the result is an integer. The result is always rounded towards minus infinity: 1/2 is 0, (-1)/2 is -1, 1/(-2) is -1, and (-1)/(-2) is 0. Note that the result is a long integer if either operand is a long integer, regardless of the numeric value.

  2. Conversion from floats using int() or long() truncates toward zero like the related function, math.trunc(). Use the function math.floor() to round downward and math.ceil() to round upward.

  3. See Fonctions Natives for a full description.

  4. Obsolète depuis la version 2.3: The floor division operator, the modulo operator, and the divmod() function are no longer defined for complex numbers. Instead, convert to a floating point number using the abs() function if appropriate.

  5. Also referred to as integer division. The resultant value is a whole integer, though the result’s type is not necessarily int.

  6. float accepte aussi les chaînes “nan” et “inf” avec un préfixe optionnel “+” ou “-” pour Not a Number (NaN) et les infinis positif ou négatif.

    Nouveau dans la version 2.6.

  7. Python définit pow(0, 0) et 0 ** 0 valant 1, ​puisque c’est courant pour les langages de programmation, et logique.

All numbers.Real types (int, long, and float) also include the following operations:

Opération

Résultat

math.trunc(x) x truncated to Integral
round(x[, n]) x rounded to n digits, rounding ties away from zero. If n is omitted, it defaults to 0.
math.floor(x) the greatest integer as a float <= x
math.ceil(x) the least integer as a float >= x

5.4.1. Opérations sur les bits des nombres entiers

Les opérations sur les bits n’ont de sens que pour les entiers. Les nombres négatifs sont traités comme leur complément à 2 (ce qui suppose un assez grand nombre de bits afin qu’aucun débordement ne se produise pendant l’opération).

Les priorités de toutes les opération à deux opérandes sur des bits sont inférieures aux opérations numériques et plus élevées que les comparaisons; l’opération unaire ~ a la même priorité que les autres opérations numériques unaires (+ et -).

Ce tableau répertorie les opérations binaires triées par priorité ascendante :

Opération

Résultat

Notes
x | y

ou <or> binaire de x et y

 
x ^ y

ou <or> exclusive binaire de x et y

 
x & y

et binaire <and> de x et y

 
x << n

x décalé vers la gauche de n bits

(1)(2)
x >> n

x décalé vers la droite de n bits

(1)(3)
~x

les bits de x, inversés

 

Notes :

  1. Des valeurs de décalage négatives sont illégales et provoquent une exception ValueError.

  2. A left shift by n bits is equivalent to multiplication by pow(2, n). A long integer is returned if the result exceeds the range of plain integers.
  3. A right shift by n bits is equivalent to division by pow(2, n).

5.4.2. Méthodes supplémentaires sur les entiers

The integer types implement the numbers.Integral abstract base class. In addition, they provide one more method:

int.bit_length()
long.bit_length()

Renvoie le nombre de bits nécessaires pour représenter un nombre entier en binaire, à l’exclusion du signe et des zéros non significatifs :

>>> n = -37
>>> bin(n)
'-0b100101'
>>> n.bit_length()
6

Plus précisément, si x est différent de zéro, x.bit_length() est le nombre entier positif unique, k tel que 2**(k-1) <= abs(x) < 2**k. Équivalemment, quand abs(x) est assez petit pour avoir un logarithme correctement arrondi, k = 1 + int(log(abs(x), 2)). Si x est nul, alors x.bit_length() donne 0.

Équivalent à :

def bit_length(self):
    s = bin(self)       # binary representation:  bin(-37) --> '-0b100101'
    s = s.lstrip('-0b') # remove leading zeros and minus sign
    return len(s)       # len('100101') --> 6

Nouveau dans la version 2.7.

5.4.3. Méthodes supplémentaires sur les nombres à virgule flottante

Le type float implémente la classe de base abstraite numbers.Real et a également les méthodes suivantes.

float.as_integer_ratio()

Renvoie une paire de nombres entiers dont le rapport est exactement égal au nombre d’origine et avec un dénominateur positif. Lève OverflowError avec un infini et ValueError avec un NaN.

Nouveau dans la version 2.6.

float.is_integer()

Donne True si l’instance de float est finie avec une valeur entière, et False autrement :

>>> (-2.0).is_integer()
True
>>> (3.2).is_integer()
False

Nouveau dans la version 2.6.

Deux méthodes prennent en charge la conversion vers et à partir de chaînes hexadécimales. Étant donné que les float de Python sont stockés en interne sous forme de nombres binaires, la conversion d’un float depuis ou vers une chaine décimale implique généralement une petite erreur d’arrondi. En revanche, les chaînes hexadécimales permettent de représenter exactement les nombres à virgule flottante. Cela peut être utile lors du débogage, et dans un travail numérique.

float.hex()

Donne une représentation d’un nombre à virgule flottante sous forme de chaîne hexadécimale. Pour les nombres à virgule flottante finis, cette représentation comprendra toujours un préfixe 0x, un suffixe p, et un exposant.

Nouveau dans la version 2.6.

float.fromhex(s)

Méthode de classe pour obtenir le float représenté par une chaîne de caractères hexadécimale s. La chaîne s peut contenir des espaces avant et après le chiffre.

Nouveau dans la version 2.6.

Notez que float.hex() est une méthode d’instance, alors que float.fromhex() est une méthode de classe.

Une chaîne hexadécimale prend la forme :

[sign] ['0x'] integer ['.' fraction] ['p' exponent]

sign peut être soit + soit -, integer et fraction sont des chaînes de chiffres hexadécimales, et exponent est un entier décimal facultativement signé. La casse n’est pas significative, et il doit y avoir au moins un chiffre hexadécimal soit dans le nombre entier soit dans la fraction. Cette syntaxe est similaire à la syntaxe spécifiée dans la section 6.4.4.2 de la norme C99, et est aussi la syntaxe utilisée à partir de Java 1.5. En particulier, la sortie de float.hex() est utilisable comme valeur hexadécimale à virgule flottante littérale en C ou Java, et des chaînes hexadécimales produites en C via un format %a ou Java via Double.toHexString sont acceptées par float.fromhex().

Notez que l’exposant est écrit en décimal plutôt qu’en hexadécimal, et qu’il donne la puissance de 2 par lequel multiplier le coefficient. Par exemple, la chaîne hexadécimale 0x3.a7p10 représente le nombre à virgule flottante (3 + 10./16 + 7./16**2) *2.0**10, ou 3740.0

>>> float.fromhex('0x3.a7p10')
3740.0

L’application de la conversion inverse à 3740.0 donne une chaîne hexadécimale différente représentant le même nombre

>>> float.hex(3740.0)
'0x1.d380000000000p+11'

5.5. Les types Itérateurs

Nouveau dans la version 2.2.

Python supporte un concept d’itération sur les conteneurs. C’est implémenté en utilisant deux méthodes distinctes qui permettent aux classes définies par l’utilisateur de devenir itérables. Les séquences, décrites plus bas en détail, supportent toujours les méthodes d’itération.

Une méthode doit être définie afin que les objets conteneurs supportent l’itération :

container.__iter__()

Donne un objet itérateur. L’objet doit implémenter le protocole d’itération décrit ci-dessous. Si un conteneur prend en charge différents types d’itération, d’autres méthodes peuvent être fournies pour obtenir spécifiquement les itérateurs pour ces types d’itération. (Exemple d’un objet supportant plusieurs formes d’itération : une structure d’arbre pouvant être parcourue en largeur ou en profondeur.) Cette méthode correspond à l’attribut tp_iter de la structure du type des objets Python dans l’API Python/C.

Les itérateurs eux-mêmes doivent implémenter les deux méthodes suivantes, qui forment ensemble le protocole d’itérateur <iterator protocol> :

iterator.__iter__()

Donne l’objet itérateur lui-même. Cela est nécessaire pour permettre à la fois à des conteneurs et des itérateurs d’être utilisés avec les instructions for et in. Cette méthode correspond à l’attribut tp_iter de la structure des types des objets Python dans l’API Python/C.

iterator.next()

Donne l’élément suivant du conteneur. S’il n’y a pas d’autres éléments, une exception StopIteration est levée. Cette méthode correspond à l’attribut PyTypeObject.tp_iternext de la structure du type des objets Python dans l’API Python/C.

Python définit plusieurs objets itérateurs pour itérer sur les types standards ou spécifiques de séquence, de dictionnaires et d’autres formes plus spécialisées. Les types spécifiques ne sont pas importants au-delà de leur implémentation du protocole d’itération.

The intention of the protocol is that once an iterator’s next() method raises StopIteration, it will continue to do so on subsequent calls. Implementations that do not obey this property are deemed broken. (This constraint was added in Python 2.3; in Python 2.2, various iterators are broken according to this rule.)

5.5.1. Types Générateurs

Python’s generators provide a convenient way to implement the iterator protocol. If a container object’s __iter__() method is implemented as a generator, it will automatically return an iterator object (technically, a generator object) supplying the __iter__() and next() methods. More information about generators can be found in the documentation for the yield expression.

5.6. Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange

There are seven sequence types: strings, Unicode strings, lists, tuples, bytearrays, buffers, and xrange objects.

For other containers see the built in dict and set classes, and the collections module.

String literals are written in single or double quotes: 'xyzzy', "frobozz". See String literals for more about string literals. Unicode strings are much like strings, but are specified in the syntax using a preceding 'u' character: u'abc', u"def". In addition to the functionality described here, there are also string-specific methods described in the Méthodes de chaînes de caractères section. Lists are constructed with square brackets, separating items with commas: [a, b, c]. Tuples are constructed by the comma operator (not within square brackets), with or without enclosing parentheses, but an empty tuple must have the enclosing parentheses, such as a, b, c or (). A single item tuple must have a trailing comma, such as (d,).

Bytearray objects are created with the built-in function bytearray().

Buffer objects are not directly supported by Python syntax, but can be created by calling the built-in function buffer(). They don’t support concatenation or repetition.

Objects of type xrange are similar to buffers in that there is no specific syntax to create them, but they are created using the xrange() function. They don’t support slicing, concatenation or repetition, and using in, not in, min() or max() on them is inefficient.

Most sequence types support the following operations. The in and not in operations have the same priorities as the comparison operations. The + and * operations have the same priority as the corresponding numeric operations. [3] Additional methods are provided for Types de séquences mutables.

This table lists the sequence operations sorted in ascending priority. In the table, s and t are sequences of the same type; n, i and j are integers:

Opération

Résultat

Notes
x in s

True si un élément de s est égal à x, sinon False

(1)
x not in s

False si un élément de s est égal à x, sinon True

(1)
s + t

la concaténation de s et t

(6)
s * n, n * s

équivalent à ajouter s n fois à lui même

(2)
s[i]

ième élément de s en commençant par 0

(3)
s[i:j]

tranche (slice) de s de i à j

(3)(4)
s[i:j:k]

tranche (slice) de s de i à j avec un pas de k

(3)(5)
len(s)

longueur de s

 
min(s)

plus petit élément de s

 
max(s)

plus grand élément de s

 
s.index(x) index of the first occurrence of x in s  
s.count(x)

nombre total d’occurrences de x dans s

 

Sequence types also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length. (For full details see Comparaisons in the language reference.)

Notes :

  1. When s is a string or Unicode string object the in and not in operations act like a substring test. In Python versions before 2.3, x had to be a string of length 1. In Python 2.3 and beyond, x may be a string of any length.

  2. Values of n less than 0 are treated as 0 (which yields an empty sequence of the same type as s). Note that items in the sequence s are not copied; they are referenced multiple times. This often haunts new Python programmers; consider:

    >>> lists = [[]] * 3
    >>> lists
    [[], [], []]
    >>> lists[0].append(3)
    >>> lists
    [[3], [3], [3]]
    

    What has happened is that [[]] is a one-element list containing an empty list, so all three elements of [[]] * 3 are references to this single empty list. Modifying any of the elements of lists modifies this single list. You can create a list of different lists this way:

    >>> lists = [[] for i in range(3)]
    >>> lists[0].append(3)
    >>> lists[1].append(5)
    >>> lists[2].append(7)
    >>> lists
    [[3], [5], [7]]
    

    De plus amples explications sont disponibles dans la FAQ à la question Comment puis-je créer une liste à plusieurs dimensions?.

  3. Si i ou j sont négatifs, l’indice est relatif à la fin de la chaîne : len(s) + i ou len(s) + j est substitué. Mais notez que -0 est toujours 0.

  4. La tranche de s de i à j est définie comme la séquence d’éléments d’indice k tels que i <= k < j. Si i ou j est supérieur à len(s), len(s) est utilisé. Si i est omis ou None, 0 est utilisé. Si j est omis ou None, len(s) est utilisé. Si i est supérieure ou égale à j, la tranche est vide.

  5. La tranche de s de i à j avec un pas de k est définie comme la séquence d’éléments d’indice x = i + n*k tels que 0 <= n < (j-i)/k. En d’autres termes, les indices sont i, i+k, i+2*k, i+3*k et ainsi de suite, en arrêtant lorsque j est atteint (mais jamais inclus). Si i ou j est supérieur à len(s), len(s) est utilisé. Si i ou j sont omis ou None, ils deviennent des valeurs “extrêmes” (où l’ordre dépend du signe de k). Remarquez, k ne peut pas valoir zéro. Si k est None, il est traité comme 1.

  6. CPython implementation detail: If s and t are both strings, some Python implementations such as CPython can usually perform an in-place optimization for assignments of the form s = s + t or s += t. When applicable, this optimization makes quadratic run-time much less likely. This optimization is both version and implementation dependent. For performance sensitive code, it is preferable to use the str.join() method which assures consistent linear concatenation performance across versions and implementations.

    Modifié dans la version 2.4: Formerly, string concatenation never occurred in-place.

5.6.1. Méthodes de chaînes de caractères

Below are listed the string methods which both 8-bit strings and Unicode objects support. Some of them are also available on bytearray objects.

In addition, Python’s strings support the sequence type methods described in the Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange section. To output formatted strings use template strings or the % operator described in the String Formatting Operations section. Also, see the re module for string functions based on regular expressions.

str.capitalize()

Renvoie une copie de la chaîne avec son premier caractère en majuscule et le reste en minuscule.

For 8-bit strings, this method is locale-dependent.

str.center(width[, fillchar])

Return centered in a string of length width. Padding is done using the specified fillchar (default is a space).

Modifié dans la version 2.4: Support for the fillchar argument.

str.count(sub[, start[, end]])

Donne le nombre d’occurrences de sub ne se chevauchant pas dans le range [start, end]. Les arguments facultatifs start et end sont interprétés comme pour des slices.

str.decode([encoding[, errors]])

Decodes the string using the codec registered for encoding. encoding defaults to the default string encoding. errors may be given to set a different error handling scheme. The default is 'strict', meaning that encoding errors raise UnicodeError. Other possible values are 'ignore', 'replace' and any other name registered via codecs.register_error(), see section Codec Base Classes.

Nouveau dans la version 2.2.

Modifié dans la version 2.3: Support for other error handling schemes added.

Modifié dans la version 2.7: Gestion des arguments par mot clef.

str.encode([encoding[, errors]])

Return an encoded version of the string. Default encoding is the current default string encoding. errors may be given to set a different error handling scheme. The default for errors is 'strict', meaning that encoding errors raise a UnicodeError. Other possible values are 'ignore', 'replace', 'xmlcharrefreplace', 'backslashreplace' and any other name registered via codecs.register_error(), see section Codec Base Classes. For a list of possible encodings, see section Standard Encodings.

Nouveau dans la version 2.0.

Modifié dans la version 2.3: Support for 'xmlcharrefreplace' and 'backslashreplace' and other error handling schemes added.

Modifié dans la version 2.7: Gestion des arguments par mot clef.

str.endswith(suffix[, start[, end]])

Donne True si la chaîne se termine par suffix, sinon False. suffix peut aussi être un tuple de suffixes à rechercher. Si l’argument optionnel start est donné, le test se fait à partir de cette position. Si l’argument optionnel end est fourni, la comparaison s’arrête à cette position.

Modifié dans la version 2.5: Accept tuples as suffix.

str.expandtabs([tabsize])

Donne une copie de la chaîne où toutes les tabulations sont remplacées par un ou plusieurs espaces, en fonction de la colonne courante et de la taille de tabulation donnée. Les positions des tabulations se trouvent tous les tabsize caractères (8 par défaut, ce qui donne les positions de tabulations aux colonnes 0, 8, 16 et ainsi de suite). Pour travailler sur la chaîne, la colonne en cours est mise à zéro et la chaîne est examinée caractère par caractère. Si le caractère est une tabulation (\t), un ou plusieurs caractères d’espacement sont insérés dans le résultat jusqu’à ce que la colonne courante soit égale à la position de tabulation suivante. (Le caractère tabulation lui-même n’est pas copié.) Si le caractère est un saut de ligne (\n) ou un retour chariot (\r), il est copié et la colonne en cours est remise à zéro. Tout autre caractère est copié inchangé et la colonne en cours est incrémentée de un indépendamment de la façon dont le caractère est représenté lors de l’affichage.

>>> '01\t012\t0123\t01234'.expandtabs()
'01      012     0123    01234'
>>> '01\t012\t0123\t01234'.expandtabs(4)
'01  012 0123    01234'
str.find(sub[, start[, end]])

Donne la première la position dans la chaîne où sub est trouvé dans le slice s[start:end]. Les arguments facultatifs start et end sont interprétés comme dans la notation des slice. Donne -1 si sub n’est pas trouvé.

Note

La méthode find() ne doit être utilisée que si vous avez besoin de connaître la position de sub. Pour vérifier si sub est une sous chaine ou non, utilisez l’opérateur in

>>> 'Py' in 'Python'
True
str.format(*args, **kwargs)

Formatte une chaîne. La chaîne sur laquelle cette méthode est appelée peut contenir du texte littéral ou des emplacements de remplacement délimités par des accolades {}. Chaque champ de remplacement contient soit l’indice numérique d’un argument positionnel, ou le nom d’un argument donné par mot-clé. Renvoie une copie de la chaîne où chaque champ de remplacement est remplacé par la valeur de chaîne de l’argument correspondant.

>>> "The sum of 1 + 2 is {0}".format(1+2)
'The sum of 1 + 2 is 3'

Voir Syntaxe de formatage de chaîne pour une description des options de formatage qui peuvent être spécifiées dans les chaînes de format.

This method of string formatting is the new standard in Python 3, and should be preferred to the % formatting described in String Formatting Operations in new code.

Nouveau dans la version 2.6.

str.index(sub[, start[, end]])

Like find(), but raise ValueError when the substring is not found.

str.isalnum()

Return true if all characters in the string are alphanumeric and there is at least one character, false otherwise.

For 8-bit strings, this method is locale-dependent.

str.isalpha()

Return true if all characters in the string are alphabetic and there is at least one character, false otherwise.

For 8-bit strings, this method is locale-dependent.

str.isdigit()

Return true if all characters in the string are digits and there is at least one character, false otherwise.

For 8-bit strings, this method is locale-dependent.

str.islower()

Donne True si tous les caractères capitalisables [4] de la chaîne sont en minuscules et qu’elle contient au moins un caractère capitalisable. Donne False dans le cas contraire.

For 8-bit strings, this method is locale-dependent.

str.isspace()

Return true if there are only whitespace characters in the string and there is at least one character, false otherwise.

For 8-bit strings, this method is locale-dependent.

str.istitle()

Donne True si la chaîne est une chaîne titlecased et qu’elle contient au moins un caractère, par exemple les caractères majuscules ne peuvent suivre les caractères non capitalisables et les caractères minuscules ne peuvent suivre que des caractères capitalisables. Donne False dans le cas contraire.

For 8-bit strings, this method is locale-dependent.

str.isupper()

Donne True si tous les caractères différentiables sur la casse [4] de la chaîne sont en majuscules et il y a au moins un caractère différentiable sur la casse, sinon False.

For 8-bit strings, this method is locale-dependent.

str.join(iterable)

Return a string which is the concatenation of the strings in the iterable iterable. The separator between elements is the string providing this method.

str.ljust(width[, fillchar])

Return the string left justified in a string of length width. Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than or equal to len(s).

Modifié dans la version 2.4: Support for the fillchar argument.

str.lower()

Renvoie une copie de la chaîne avec tous les caractères capitalisables [4] convertis en minuscules.

For 8-bit strings, this method is locale-dependent.

str.lstrip([chars])

Return a copy of the string with leading characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix; rather, all combinations of its values are stripped:

>>> '   spacious   '.lstrip()
'spacious   '
>>> 'www.example.com'.lstrip('cmowz.')
'example.com'

Modifié dans la version 2.2.2: Support for the chars argument.

str.partition(sep)

Divise la chaîne à la première occurrence de sep, et donne un tuple de trois éléments contenant la partie avant le séparateur, le séparateur lui-même, et la partie après le séparateur. Si le séparateur n’est pas trouvé, le tuple contiendra la chaîne elle-même, suivie de deux chaînes vides.

Nouveau dans la version 2.5.

str.replace(old, new[, count])

Renvoie une copie de la chaîne dont toutes les occurrences de la sous-chaîne old sont remplacés par new. Si l’argument optionnel count est donné, seules les count premières occurrences sont remplacées.

str.rfind(sub[, start[, end]])

Donne l’indice le plus élevé dans la chaîne où la sous-chaîne sub se trouve, de telle sorte que sub soit contenue dans s[start:end]. Les arguments facultatifs start et end sont interprétés comme dans la notation des slices. Donne -1 en cas d’échec.

str.rindex(sub[, start[, end]])

Comme rfind() mais lève une exception ValueError lorsque la sous-chaîne sub est introuvable.

str.rjust(width[, fillchar])

Return the string right justified in a string of length width. Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than or equal to len(s).

Modifié dans la version 2.4: Support for the fillchar argument.

str.rpartition(sep)

Divise la chaîne à la dernière occurrence de sep, et donne un tuple de trois éléments contenant la partie avant le séparateur, le séparateur lui-même, et la partie après le séparateur. Si le séparateur n’est pas trouvé, le tuple contindra deux chaînes vides, puis par la chaîne elle-même.

Nouveau dans la version 2.5.

str.rsplit([sep[, maxsplit]])

Renvoie une liste des mots de la chaîne, en utilisant sep comme séparateur. Si maxsplit est donné, c’est le nombre maximum de divisions qui pourront être faites, celles “à droite”. Si sep est pas spécifié ou est None, tout espace est un séparateur. En dehors du fait qu’il découpe par la droite, rsplit() se comporte comme split() qui est décrit en détail ci-dessous.

Nouveau dans la version 2.4.

str.rstrip([chars])

Return a copy of the string with trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a suffix; rather, all combinations of its values are stripped:

>>> '   spacious   '.rstrip()
'   spacious'
>>> 'mississippi'.rstrip('ipz')
'mississ'

Modifié dans la version 2.2.2: Support for the chars argument.

str.split([sep[, maxsplit]])

Renvoie une liste des mots de la chaîne, en utilisant sep comme séparateur de mots. Si maxsplit est donné, c’est le nombre maximum de divisionsqui pourront être effectuées, (donnant ainsi une liste de longueur maxsplit+1). Si maxsplit n’est pas fourni, ou vaut -1, le nombre de découpes n’est pas limité (Toutes les découpes possibles sont faites).

Si sep est donné, les délimiteurs consécutifs ne sont pas regroupés et ainsi délimitent des chaînes vides (par exemple, '1,,2'.split(',') donne ['1', '', '2']). L’argument sep peut contenir plusieurs caractères (par exemple, '1<>2<>3'.split('<>') retourne ['1', '2', '3']). Découper une chaîne vide en spécifiant sep donne [''].

Si sep n’est pas spécifié ou est None, un autre algorithme de découpage est appliqué : les espaces consécutifs sont considérés comme un seul séparateur, et le résultat ne contiendra pas les chaînes vides de début ou de la fin si la chaîne est préfixée ou suffixé d’espaces. Par conséquent, diviser une chaîne vide ou une chaîne composée d’espaces avec un séparateur None renvoie [].

For example, ' 1  2   3  '.split() returns ['1', '2', '3'], and '  1  2   3  '.split(None, 1) returns ['1', '2   3  '].

str.splitlines([keepends])

Return a list of the lines in the string, breaking at line boundaries. This method uses the universal newlines approach to splitting lines. Line breaks are not included in the resulting list unless keepends is given and true.

Python recognizes "\r", "\n", and "\r\n" as line boundaries for 8-bit strings.

Par exemple :

>>> 'ab c\n\nde fg\rkl\r\n'.splitlines()
['ab c', '', 'de fg', 'kl']
>>> 'ab c\n\nde fg\rkl\r\n'.splitlines(True)
['ab c\n', '\n', 'de fg\r', 'kl\r\n']

Unlike split() when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:

>>> "".splitlines()
[]
>>> "One line\n".splitlines()
['One line']

For comparison, split('\n') gives:

>>> ''.split('\n')
['']
>>> 'Two lines\n'.split('\n')
['Two lines', '']
unicode.splitlines([keepends])

Return a list of the lines in the string, like str.splitlines(). However, the Unicode method splits on the following line boundaries, which are a superset of the universal newlines recognized for 8-bit strings.

Representation Description
\n Line Feed
\r Carriage Return
\r\n Carriage Return + Line Feed
\v or \x0b Line Tabulation
\f or \x0c Form Feed
\x1c File Separator
\x1d Group Separator
\x1e Record Separator
\x85 Next Line (C1 Control Code)
\u2028 Line Separator
\u2029 Paragraph Separator

Modifié dans la version 2.7: \v and \f added to list of line boundaries.

str.startswith(prefix[, start[, end]])

Donne True si la chaîne commence par prefix, sinon False. prefix peut aussi être un tuple de préfixes à rechercher. Lorsque start est donné, la comparaison commence à cette position, et lorsque end est donné, la comparaison s’arrête à celle ci.

Modifié dans la version 2.5: Accept tuples as prefix.

str.strip([chars])

Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped:

>>> '   spacious   '.strip()
'spacious'
>>> 'www.example.com'.strip('cmowz.')
'example'

Modifié dans la version 2.2.2: Support for the chars argument.

str.swapcase()

Return a copy of the string with uppercase characters converted to lowercase and vice versa.

For 8-bit strings, this method is locale-dependent.

str.title()

Renvoie une version en initiales majuscules de la chaîne où les mots commencent par une capitale et les caractères restants sont en minuscules.

Pour l’algorithme, la notion de mot est définie simplement et indépendamment de la langue comme un groupe de lettres consécutives. La définition fonctionnedans de nombreux contextes, mais cela signifie que les apostrophes (typiquement dela forme possessive en Anglais) forment les limites de mot, ce qui n’est pas toujours le résultat souhaité :

>>> "they're bill's friends from the UK".title()
"They'Re Bill'S Friends From The Uk"

Une solution pour contourner le problème des apostrophes peut être obtenue en utilisant des expressions rationnelles :

>>> import re
>>> def titlecase(s):
...     return re.sub(r"[A-Za-z]+('[A-Za-z]+)?",
...                   lambda mo: mo.group(0)[0].upper() +
...                              mo.group(0)[1:].lower(),
...                   s)
...
>>> titlecase("they're bill's friends.")
"They're Bill's Friends."

For 8-bit strings, this method is locale-dependent.

str.translate(table[, deletechars])

Return a copy of the string where all characters occurring in the optional argument deletechars are removed, and the remaining characters have been mapped through the given translation table, which must be a string of length 256.

You can use the maketrans() helper function in the string module to create a translation table. For string objects, set the table argument to None for translations that only delete characters:

>>> 'read this short text'.translate(None, 'aeiou')
'rd ths shrt txt'

Nouveau dans la version 2.6: Support for a None table argument.

For Unicode objects, the translate() method does not accept the optional deletechars argument. Instead, it returns a copy of the s where all characters have been mapped through the given translation table which must be a mapping of Unicode ordinals to Unicode ordinals, Unicode strings or None. Unmapped characters are left untouched. Characters mapped to None are deleted. Note, a more flexible approach is to create a custom character mapping codec using the codecs module (see encodings.cp1251 for an example).

str.upper()

Renvoie une copie de la chaîne dont tous les caractères capitalisables [4] sontconvertis en capitales. Notez que str.upper().isupper() pourrait être False si s contient des caractères non capitalisables ou si la catégorieUnicode d’un caractère du résultant est pas “Lu” (Lettre, majuscule), mais par exemple “Lt” (Lettre, titlecase).

For 8-bit strings, this method is locale-dependent.

str.zfill(width)

Return the numeric string left filled with zeros in a string of length width. A sign prefix is handled correctly. The original string is returned if width is less than or equal to len(s).

Nouveau dans la version 2.2.2.

The following methods are present only on unicode objects:

unicode.isnumeric()

Return True if there are only numeric characters in S, False otherwise. Numeric characters include digit characters, and all characters that have the Unicode numeric value property, e.g. U+2155, VULGAR FRACTION ONE FIFTH.

unicode.isdecimal()

Return True if there are only decimal characters in S, False otherwise. Decimal characters include digit characters, and all characters that can be used to form decimal-radix numbers, e.g. U+0660, ARABIC-INDIC DIGIT ZERO.

5.6.2. String Formatting Operations

String and Unicode objects have one unique built-in operation: the % operator (modulo). This is also known as the string formatting or interpolation operator. Given format % values (where format is a string or Unicode object), % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to the using sprintf() in the C language. If format is a Unicode object, or if any of the objects being converted using the %s conversion are Unicode objects, the result will also be a Unicode object.

Si format ne nécessite qu’un seul argument, values peut être un objet unique. [5] Si values est un tuple, il doit contenir exactement lenombre d’éléments spécifiés par la chaîne de format, ou un seul objet de correspondances ( mapping object, par exemple, un dictionnaire).

Un indicateur de conversion contient deux ou plusieurs caractères et comporte les éléments suivants, qui doivent apparaître dans cet ordre :

  1. Le caractère '%', qui marque le début du marqueur.

  2. La clé de correspondance (facultative), composée d’une suite de caractères entre parenthèse (par exemple, (somename)).

  3. Des options de conversion, facultatives, qui affectent le résultat de certains types de conversion.

  4. Largeur minimum (facultative). Si elle vaut '*' (astérisque), la largeur est lue de l’élément suivant du tuple values, et l’objet à convertir vient après la largeur de champ minimale et la précision facultative.

  5. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual width is read from the next element of the tuple in values, and the value to convert comes after the precision.
  6. Modificateur de longueur (facultatif).

  7. Type de conversion.

Lorsque l’argument de droite est un dictionnaire (ou un autre type de mapping), les marqueurs dans la chaîne doivent inclure une clé présente dans le dictionnaire, écrite entre parenthèses, immédiatement après le caractère '%'. La clé indique quelle valeur du dictionnaire doit être formatée. Par exemple :

>>> print '%(language)s has %(number)03d quote types.' % \
...       {"language": "Python", "number": 2}
Python has 002 quote types.

Dans ce cas, aucune * ne peuvent se trouver dans le format (car ces * nécessitent une liste (accès séquentiel) de paramètres).

Les caractères indicateurs de conversion sont :

Option

Signification

'#'

La conversion utilisera la “forme alternative” (définie ci-dessous).

'0'

Les valeurs numériques converties seront complétée de zéros.

'-'

La valeur convertie est ajustée à gauche (remplace la conversion '0' si les deux sont données).

' '

(un espace) Un espace doit être laissé avant un nombre positif (ou chaîne vide) produite par la conversion d’une valeur signée.

'+'

Un caractère de signe ('+' ou '-') précéde la valeur convertie (remplace le marqueur “espace”).

Un modificateur de longueur (h, l ou L) peut être présent, mais est ignoré car il est pas nécessaire pour Python - donc par exemple %ld est identique à %d.

Les types utilisables dans les conversion sont :

Conversion

Signification

Notes
'd'

Entier décimal signé.

 
'i'

Entier décimal signé.

 
'o'

Valeur octale signée.

(1)
'u'

Type obsolète - identique à 'd'.

(7)
'x'

Hexadécimal signé (en minuscules).

(2)
'X'

Hexadécimal signé (capitales).

(2)
'e'

Format exponentiel pour un float (minuscule).

(3)
'E'

Format exponentiel pour un float (en capitales).

(3)
'f'

Format décimal pour un float.

(3)
'F'

Format décimal pour un float.

(3)
'g'

Format float. Utilise le format exponentiel minuscules si l’exposant est inférieur à -4 ou pas plus petit que la précision, sinon le format décimal.

(4)
'G'

Format float. Utilise le format exponentiel en capitales si l’exposant est inférieur à -4 ou pas plus petit que la précision, sinon le format décimal.

(4)
'c'

Un seul caractère (accepte des entiers ou une chaîne d’un seul caractère).

 
'r' String (converts any Python object using repr()). (5)
's'

String (convertit n’importe quel objet Python avec str()).

(6)
'%'

Aucun argument n’est converti, donne un caractère de '%' dans le résultat.

 

Notes :

  1. La forme alternative insère un zéro ('0') entre le rembourrage gauche et le formatage du nombre si son premier caractère n’est pas déjà un zéro.

  2. La forme alternative insère '0x' ou '0X' (respectivement pour les formats 'x' et 'X') entre le rembourrage de gauche et nombre formaté, si le premier caractère n’est pas déjà un zéro.

  3. La forme alternative implique la présence d’un point décimal, même si aucun chiffre ne le suit.

    La précision détermine le nombre de chiffres après la virgule, 6 par défaut.

  4. La forme alternative implique la présence d’un point décimal et les zéros non significatifs sont conservés (ils ne le seraient pas autrement).

    La précision détermine le nombre de chiffres significatifs avant et après la virgule. 6 par défaut.

  5. The %r conversion was added in Python 2.0.

    The precision determines the maximal number of characters used.

  6. If the object or format provided is a unicode string, the resulting string will also be unicode.

    The precision determines the maximal number of characters used.

  7. Voir la PEP 237.

Puisque les chaînes Python ont une longueur explicite, les conversions %s ne considèrent pas '\0' comme la fin de la chaîne.

Modifié dans la version 2.7: Les conversions %f pour nombres dont la valeur absolue est supérieure à 1e50 ne sont plus remplacés par des conversions %g.

Additional string operations are defined in standard modules string and re.

5.6.3. XRange Type

The xrange type is an immutable sequence which is commonly used for looping. The advantage of the xrange type is that an xrange object will always take the same amount of memory, no matter the size of the range it represents. There are no consistent performance advantages.

XRange objects have very little behavior: they only support indexing, iteration, and the len() function.

5.6.4. Types de séquences mutables

List and bytearray objects support additional operations that allow in-place modification of the object. Other mutable sequence types (when added to the language) should also support these operations. Strings and tuples are immutable sequence types: such objects cannot be modified once created. The following operations are defined on mutable sequence types (where x is an arbitrary object):

Opération

Résultat

Notes
s[i] = x

element i de s est remplacé par x

 
s[i:j] = t

tranche de s de i à j est remplacée par le contenu de l’itérable t

 
del s[i:j]

identique à s[i:j] = []

 
s[i:j:k] = t

les éléments de s[i:j:k] sont remplacés par ceux de t

(1)
del s[i:j:k]

supprime les éléments de s[i:j:k] de la liste

 
s.append(x) same as s[len(s):len(s)] = [x] (2)
s.extend(x) or s += t for the most part the same as s[len(s):len(s)] = x (3)
s *= n

met à jour s avec son contenu répété n fois

(11)
s.count(x) return number of i‘s for which s[i] == x  
s.index(x[, i[, j]]) return smallest k such that s[k] == x and i <= k < j (4)
s.insert(i, x) same as s[i:i] = [x] (5)
s.pop([i]) same as x = s[i]; del s[i]; return x (6)
s.remove(x) same as del s[s.index(x)] (4)
s.reverse()

inverse sur place les éléments de s

(7)
s.sort([cmp[, key[, reverse]]]) sort the items of s in place (7)(8)(9)(10)

Notes :

  1. t must have the same length as the slice it is replacing.

  2. The C implementation of Python has historically accepted multiple parameters and implicitly joined them into a tuple; this no longer works in Python 2.0. Use of this misfeature has been deprecated since Python 1.4.

  3. x can be any iterable object.

  4. Raises ValueError when x is not found in s. When a negative index is passed as the second or third parameter to the index() method, the list length is added, as for slice indices. If it is still negative, it is truncated to zero, as for slice indices.

    Modifié dans la version 2.3: Previously, index() didn’t have arguments for specifying start and stop positions.

  5. When a negative index is passed as the first parameter to the insert() method, the list length is added, as for slice indices. If it is still negative, it is truncated to zero, as for slice indices.

    Modifié dans la version 2.3: Previously, all negative indices were truncated to zero.

  6. The pop() method’s optional argument i defaults to -1, so that by default the last item is removed and returned.

  7. The sort() and reverse() methods modify the list in place for economy of space when sorting or reversing a large list. To remind you that they operate by side effect, they don’t return the sorted or reversed list.

  8. The sort() method takes optional arguments for controlling the comparisons.

    cmp specifies a custom comparison function of two arguments (list items) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument: cmp=lambda x,y: cmp(x.lower(), y.lower()). The default value is None.

    key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None.

    reverse, une valeur booléenne. Si elle est True, la liste d’éléments est triée comme si toutes les comparaisons étaient inversées.

    In general, the key and reverse conversion processes are much faster than specifying an equivalent cmp function. This is because cmp is called multiple times for each list element while key and reverse touch each element only once. Use functools.cmp_to_key() to convert an old-style cmp function to a key function.

    Modifié dans la version 2.3: Support for None as an equivalent to omitting cmp was added.

    Modifié dans la version 2.4: Support for key and reverse was added.

  9. Starting with Python 2.3, the sort() method is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

  10. CPython implementation detail: While a list is being sorted, the effect of attempting to mutate, or even inspect, the list is undefined. The C implementation of Python 2.3 and newer makes the list appear empty for the duration, and raises ValueError if it can detect that the list has been mutated during a sort.

  11. The value n is an integer, or an object implementing __index__(). Zero and negative values of n clear the sequence. Items in the sequence are not copied; they are referenced multiple times, as explained for s * n under Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange.

5.7. Set Types — set, frozenset

A set object is an unordered collection of distinct hashable objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. (For other containers see the built in dict, list, and tuple classes, and the collections module.)

Nouveau dans la version 2.4.

Like other collections, sets support x in set, len(set), and for x in set. Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior.

There are currently two built-in set types, set and frozenset. The set type is mutable — the contents can be changed using methods like add() and remove(). Since it is mutable, it has no hash value and cannot be used as either a dictionary key or as an element of another set. The frozenset type is immutable and hashable — its contents cannot be altered after it is created; it can therefore be used as a dictionary key or as an element of another set.

As of Python 2.7, non-empty sets (not frozensets) can be created by placing a comma-separated list of elements within braces, for example: {'jack', 'sjoerd'}, in addition to the set constructor.

The constructors for both classes work the same:

class set([iterable])
class frozenset([iterable])

Return a new set or frozenset object whose elements are taken from iterable. The elements of a set must be hashable. To represent sets of sets, the inner sets must be frozenset objects. If iterable is not specified, a new empty set is returned.

Instances of set and frozenset provide the following operations:

len(s)

Donne le nombre d’éléments dans le set s (cardinalité de s).

x in s

Test x for membership in s.

x not in s

Test x for non-membership in s.

isdisjoint(other)

Return True if the set has no elements in common with other. Sets are disjoint if and only if their intersection is the empty set.

Nouveau dans la version 2.6.

issubset(other)
set <= other

Test whether every element in the set is in other.

set < other

Test whether the set is a proper subset of other, that is, set <= other and set != other.

issuperset(other)
set >= other

Test whether every element in other is in the set.

set > other

Test whether the set is a proper superset of other, that is, set >= other and set != other.

union(other, ...)
set | other | ...

Return a new set with elements from the set and all others.

Modifié dans la version 2.6: Accepts multiple input iterables.

intersection(other, ...)
set & other & ...

Return a new set with elements common to the set and all others.

Modifié dans la version 2.6: Accepts multiple input iterables.

difference(other, ...)
set - other - ...

Return a new set with elements in the set that are not in the others.

Modifié dans la version 2.6: Accepts multiple input iterables.

symmetric_difference(other)
set ^ other

Return a new set with elements in either the set or other but not both.

copy()

Return a new set with a shallow copy of s.

Note, the non-operator versions of union(), intersection(), difference(), and symmetric_difference(), issubset(), and issuperset() methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs').

Both set and frozenset support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).

Instances of set are compared to instances of frozenset based on their members. For example, set('abc') == frozenset('abc') returns True and so does set('abc') in set([frozenset('abc')]).

The subset and equality comparisons do not generalize to a total ordering function. For example, any two non-empty disjoint sets are not equal and are not subsets of each other, so all of the following return False: a<b, a==b, or a>b. Accordingly, sets do not implement the __cmp__() method.

Since sets only define partial ordering (subset relationships), the output of the list.sort() method is undefined for lists of sets.

Set elements, like dictionary keys, must be hashable.

Binary operations that mix set instances with frozenset return the type of the first operand. For example: frozenset('ab') | set('bc') returns an instance of frozenset.

The following table lists operations available for set that do not apply to immutable instances of frozenset:

update(other, ...)
set |= other | ...

Update the set, adding elements from all others.

Modifié dans la version 2.6: Accepts multiple input iterables.

intersection_update(other, ...)
set &= other & ...

Update the set, keeping only elements found in it and all others.

Modifié dans la version 2.6: Accepts multiple input iterables.

difference_update(other, ...)
set -= other | ...

Update the set, removing elements found in others.

Modifié dans la version 2.6: Accepts multiple input iterables.

symmetric_difference_update(other)
set ^= other

Update the set, keeping only elements found in either set, but not in both.

add(elem)

Add element elem to the set.

remove(elem)

Remove element elem from the set. Raises KeyError if elem is not contained in the set.

discard(elem)

Remove element elem from the set if it is present.

pop()

Remove and return an arbitrary element from the set. Raises KeyError if the set is empty.

clear()

Remove all elements from the set.

Note, the non-operator versions of the update(), intersection_update(), difference_update(), and symmetric_difference_update() methods will accept any iterable as an argument.

Note, the elem argument to the __contains__(), remove(), and discard() methods may be a set. To support searching for an equivalent frozenset, the elem set is temporarily mutated during the search and then restored. During the search, the elem set should not be read or mutated since it does not have a meaningful value.

Voir aussi

Comparison to the built-in set types
Differences between the sets module and the built-in set types.

5.8. Mapping Types — dict

A mapping object maps hashable values to arbitrary objects. Mappings are mutable objects. There is currently only one standard mapping type, the dictionary. (For other containers see the built in list, set, and tuple classes, and the collections module.)

A dictionary’s keys are almost arbitrary values. Values that are not hashable, that is, values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys. Numeric types used for keys obey the normal rules for numeric comparison: if two numbers compare equal (such as 1 and 1.0) then they can be used interchangeably to index the same dictionary entry. (Note however, that since computers store floating-point numbers as approximations it is usually unwise to use them as dictionary keys.)

Dictionaries can be created by placing a comma-separated list of key: value pairs within braces, for example: {'jack': 4098, 'sjoerd': 4127} or {4098: 'jack', 4127: 'sjoerd'}, or by the dict constructor.

class dict(**kwarg)
class dict(mapping, **kwarg)
class dict(iterable, **kwarg)

Return a new dictionary initialized from an optional positional argument and a possibly empty set of keyword arguments.

If no positional argument is given, an empty dictionary is created. If a positional argument is given and it is a mapping object, a dictionary is created with the same key-value pairs as the mapping object. Otherwise, the positional argument must be an iterable object. Each item in the iterable must itself be an iterable with exactly two objects. The first object of each item becomes a key in the new dictionary, and the second object the corresponding value. If a key occurs more than once, the last value for that key becomes the corresponding value in the new dictionary.

If keyword arguments are given, the keyword arguments and their values are added to the dictionary created from the positional argument. If a key being added is already present, the value from the keyword argument replaces the value from the positional argument.

To illustrate, the following examples all return a dictionary equal to {"one": 1, "two": 2, "three": 3}:

>>> a = dict(one=1, two=2, three=3)
>>> b = {'one': 1, 'two': 2, 'three': 3}
>>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
>>> d = dict([('two', 2), ('one', 1), ('three', 3)])
>>> e = dict({'three': 3, 'one': 1, 'two': 2})
>>> a == b == c == d == e
True

Providing keyword arguments as in the first example only works for keys that are valid Python identifiers. Otherwise, any valid keys can be used.

Nouveau dans la version 2.2.

Modifié dans la version 2.3: Support for building a dictionary from keyword arguments added.

These are the operations that dictionaries support (and therefore, custom mapping types should support too):

len(d)

Return the number of items in the dictionary d.

d[key]

Return the item of d with key key. Raises a KeyError if key is not in the map.

If a subclass of dict defines a method __missing__() and key is not present, the d[key] operation calls that method with the key key as argument. The d[key] operation then returns or raises whatever is returned or raised by the __missing__(key) call. No other operations or methods invoke __missing__(). If __missing__() is not defined, KeyError is raised. __missing__() must be a method; it cannot be an instance variable:

>>> class Counter(dict):
...     def __missing__(self, key):
...         return 0
>>> c = Counter()
>>> c['red']
0
>>> c['red'] += 1
>>> c['red']
1

The example above shows part of the implementation of collections.Counter. A different __missing__ method is used by collections.defaultdict.

Nouveau dans la version 2.5: Recognition of __missing__ methods of dict subclasses.

d[key] = value

Set d[key] to value.

del d[key]

Remove d[key] from d. Raises a KeyError if key is not in the map.

key in d

Return True if d has a key key, else False.

Nouveau dans la version 2.2.

key not in d

Equivalent to not key in d.

Nouveau dans la version 2.2.

iter(d)

Return an iterator over the keys of the dictionary. This is a shortcut for iterkeys().

clear()

Remove all items from the dictionary.

copy()

Return a shallow copy of the dictionary.

fromkeys(seq[, value])

Create a new dictionary with keys from seq and values set to value.

fromkeys() is a class method that returns a new dictionary. value defaults to None.

Nouveau dans la version 2.3.

get(key[, default])

Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a KeyError.

has_key(key)

Test for the presence of key in the dictionary. has_key() is deprecated in favor of key in d.

items()

Return a copy of the dictionary’s list of (key, value) pairs.

CPython implementation detail: Keys and values are listed in an arbitrary order which is non-random, varies across Python implementations, and depends on the dictionary’s history of insertions and deletions.

If items(), keys(), values(), iteritems(), iterkeys(), and itervalues() are called with no intervening modifications to the dictionary, the lists will directly correspond. This allows the creation of (value, key) pairs using zip(): pairs = zip(d.values(), d.keys()). The same relationship holds for the iterkeys() and itervalues() methods: pairs = zip(d.itervalues(), d.iterkeys()) provides the same value for pairs. Another way to create the same list is pairs = [(v, k) for (k, v) in d.iteritems()].

iteritems()

Return an iterator over the dictionary’s (key, value) pairs. See the note for dict.items().

Using iteritems() while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

Nouveau dans la version 2.2.

iterkeys()

Return an iterator over the dictionary’s keys. See the note for dict.items().

Using iterkeys() while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

Nouveau dans la version 2.2.

itervalues()

Return an iterator over the dictionary’s values. See the note for dict.items().

Using itervalues() while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

Nouveau dans la version 2.2.

keys()

Return a copy of the dictionary’s list of keys. See the note for dict.items().

pop(key[, default])

If key is in the dictionary, remove it and return its value, else return default. If default is not given and key is not in the dictionary, a KeyError is raised.

Nouveau dans la version 2.3.

popitem()

Remove and return an arbitrary (key, value) pair from the dictionary.

popitem() is useful to destructively iterate over a dictionary, as often used in set algorithms. If the dictionary is empty, calling popitem() raises a KeyError.

setdefault(key[, default])

If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.

update([other])

Update the dictionary with the key/value pairs from other, overwriting existing keys. Return None.

update() accepts either another dictionary object or an iterable of key/value pairs (as tuples or other iterables of length two). If keyword arguments are specified, the dictionary is then updated with those key/value pairs: d.update(red=1, blue=2).

Modifié dans la version 2.4: Allowed the argument to be an iterable of key/value pairs and allowed keyword arguments.

values()

Return a copy of the dictionary’s list of values. See the note for dict.items().

viewitems()

Return a new view of the dictionary’s items ((key, value) pairs). See below for documentation of view objects.

Nouveau dans la version 2.7.

viewkeys()

Return a new view of the dictionary’s keys. See below for documentation of view objects.

Nouveau dans la version 2.7.

viewvalues()

Return a new view of the dictionary’s values. See below for documentation of view objects.

Nouveau dans la version 2.7.

Dictionaries compare equal if and only if they have the same (key, value) pairs.

5.8.1. Dictionary view objects

The objects returned by dict.viewkeys(), dict.viewvalues() and dict.viewitems() are view objects. They provide a dynamic view on the dictionary’s entries, which means that when the dictionary changes, the view reflects these changes.

Dictionary views can be iterated over to yield their respective data, and support membership tests:

len(dictview)

Return the number of entries in the dictionary.

iter(dictview)

Return an iterator over the keys, values or items (represented as tuples of (key, value)) in the dictionary.

Keys and values are iterated over in an arbitrary order which is non-random, varies across Python implementations, and depends on the dictionary’s history of insertions and deletions. If keys, values and items views are iterated over with no intervening modifications to the dictionary, the order of items will directly correspond. This allows the creation of (value, key) pairs using zip(): pairs = zip(d.values(), d.keys()). Another way to create the same list is pairs = [(v, k) for (k, v) in d.items()].

Iterating views while adding or deleting entries in the dictionary may raise a RuntimeError or fail to iterate over all entries.

x in dictview

Return True if x is in the underlying dictionary’s keys, values or items (in the latter case, x should be a (key, value) tuple).

Keys views are set-like since their entries are unique and hashable. If all values are hashable, so that (key, value) pairs are unique and hashable, then the items view is also set-like. (Values views are not treated as set-like since the entries are generally not unique.) Then these set operations are available (“other” refers either to another view or a set):

dictview & other

Return the intersection of the dictview and the other object as a new set.

dictview | other

Return the union of the dictview and the other object as a new set.

dictview - other

Return the difference between the dictview and the other object (all elements in dictview that aren’t in other) as a new set.

dictview ^ other

Return the symmetric difference (all elements either in dictview or other, but not in both) of the dictview and the other object as a new set.

An example of dictionary view usage:

>>> dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
>>> keys = dishes.viewkeys()
>>> values = dishes.viewvalues()

>>> # iteration
>>> n = 0
>>> for val in values:
...     n += val
>>> print(n)
504

>>> # keys and values are iterated over in the same order
>>> list(keys)
['eggs', 'bacon', 'sausage', 'spam']
>>> list(values)
[2, 1, 1, 500]

>>> # view objects are dynamic and reflect dict changes
>>> del dishes['eggs']
>>> del dishes['sausage']
>>> list(keys)
['spam', 'bacon']

>>> # set operations
>>> keys & {'eggs', 'bacon', 'salad'}
{'bacon'}

5.9. Objets fichiers

File objects are implemented using C’s stdio package and can be created with the built-in open() function. File objects are also returned by some other built-in functions and methods, such as os.popen() and os.fdopen() and the makefile() method of socket objects. Temporary files can be created using the tempfile module, and high-level file operations such as copying, moving, and deleting files and directories can be achieved with the shutil module.

When a file operation fails for an I/O-related reason, the exception IOError is raised. This includes situations where the operation is not defined for some reason, like seek() on a tty device or writing a file opened for reading.

Files have the following methods:

file.close()

Close the file. A closed file cannot be read or written any more. Any operation which requires that the file be open will raise a ValueError after the file has been closed. Calling close() more than once is allowed.

As of Python 2.5, you can avoid having to call this method explicitly if you use the with statement. For example, the following code will automatically close f when the with block is exited:

from __future__ import with_statement # This isn't required in Python 2.6

with open("hello.txt") as f:
    for line in f:
        print line,

In older versions of Python, you would have needed to do this to get the same effect:

f = open("hello.txt")
try:
    for line in f:
        print line,
finally:
    f.close()

Note

Not all “file-like” types in Python support use as a context manager for the with statement. If your code is intended to work with any file-like object, you can use the function contextlib.closing() instead of using the object directly.

file.flush()

Flush the internal buffer, like stdio‘s fflush(). This may be a no-op on some file-like objects.

Note

flush() does not necessarily write the file’s data to disk. Use flush() followed by os.fsync() to ensure this behavior.

file.fileno()

Return the integer “file descriptor” that is used by the underlying implementation to request I/O operations from the operating system. This can be useful for other, lower level interfaces that use file descriptors, such as the fcntl module or os.read() and friends.

Note

File-like objects which do not have a real file descriptor should not provide this method!

file.isatty()

Return True if the file is connected to a tty(-like) device, else False.

Note

If a file-like object is not associated with a real file, this method should not be implemented.

file.next()

A file object is its own iterator, for example iter(f) returns f (unless f is closed). When a file is used as an iterator, typically in a for loop (for example, for line in f: print line.strip()), the next() method is called repeatedly. This method returns the next input line, or raises StopIteration when EOF is hit when the file is open for reading (behavior is undefined when the file is open for writing). In order to make a for loop the most efficient way of looping over the lines of a file (a very common operation), the next() method uses a hidden read-ahead buffer. As a consequence of using a read-ahead buffer, combining next() with other file methods (like readline()) does not work right. However, using seek() to reposition the file to an absolute position will flush the read-ahead buffer.

Nouveau dans la version 2.3.

file.read([size])

Read at most size bytes from the file (less if the read hits EOF before obtaining size bytes). If the size argument is negative or omitted, read all data until EOF is reached. The bytes are returned as a string object. An empty string is returned when EOF is encountered immediately. (For certain files, like ttys, it makes sense to continue reading after an EOF is hit.) Note that this method may call the underlying C function fread() more than once in an effort to acquire as close to size bytes as possible. Also note that when in non-blocking mode, less data than was requested may be returned, even if no size parameter was given.

Note

This function is simply a wrapper for the underlying fread() C function, and will behave the same in corner cases, such as whether the EOF value is cached.

file.readline([size])

Read one entire line from the file. A trailing newline character is kept in the string (but may be absent when a file ends with an incomplete line). [6] If the size argument is present and non-negative, it is a maximum byte count (including the trailing newline) and an incomplete line may be returned. When size is not 0, an empty string is returned only when EOF is encountered immediately.

Note

Unlike stdio‘s fgets(), the returned string contains null characters ('\0') if they occurred in the input.

file.readlines([sizehint])

Read until EOF using readline() and return a list containing the lines thus read. If the optional sizehint argument is present, instead of reading up to EOF, whole lines totalling approximately sizehint bytes (possibly after rounding up to an internal buffer size) are read. Objects implementing a file-like interface may choose to ignore sizehint if it cannot be implemented, or cannot be implemented efficiently.

file.xreadlines()

This method returns the same thing as iter(f).

Nouveau dans la version 2.1.

Obsolète depuis la version 2.3: Use for line in file instead.

file.seek(offset[, whence])

Set the file’s current position, like stdio‘s fseek(). The whence argument is optional and defaults to os.SEEK_SET or 0 (absolute file positioning); other values are os.SEEK_CUR or 1 (seek relative to the current position) and os.SEEK_END or 2 (seek relative to the file’s end). There is no return value.

For example, f.seek(2, os.SEEK_CUR) advances the position by two and f.seek(-3, os.SEEK_END) sets the position to the third to last.

Note that if the file is opened for appending (mode 'a' or 'a+'), any seek() operations will be undone at the next write. If the file is only opened for writing in append mode (mode 'a'), this method is essentially a no-op, but it remains useful for files opened in append mode with reading enabled (mode 'a+'). If the file is opened in text mode (without 'b'), only offsets returned by tell() are legal. Use of other offsets causes undefined behavior.

Note that not all file objects are seekable.

Modifié dans la version 2.6: Passing float values as offset has been deprecated.

file.tell()

Return the file’s current position, like stdio‘s ftell().

Note

On Windows, tell() can return illegal values (after an fgets()) when reading files with Unix-style line-endings. Use binary mode ('rb') to circumvent this problem.

file.truncate([size])

Truncate the file’s size. If the optional size argument is present, the file is truncated to (at most) that size. The size defaults to the current position. The current file position is not changed. Note that if a specified size exceeds the file’s current size, the result is platform-dependent: possibilities include that the file may remain unchanged, increase to the specified size as if zero-filled, or increase to the specified size with undefined new content. Availability: Windows, many Unix variants.

file.write(str)

Write a string to the file. There is no return value. Due to buffering, the string may not actually show up in the file until the flush() or close() method is called.

file.writelines(sequence)

Write a sequence of strings to the file. The sequence can be any iterable object producing strings, typically a list of strings. There is no return value. (The name is intended to match readlines(); writelines() does not add line separators.)

Files support the iterator protocol. Each iteration returns the same result as readline(), and iteration ends when the readline() method returns an empty string.

File objects also offer a number of other interesting attributes. These are not required for file-like objects, but should be implemented if they make sense for the particular object.

file.closed

bool indicating the current state of the file object. This is a read-only attribute; the close() method changes the value. It may not be available on all file-like objects.

file.encoding

The encoding that this file uses. When Unicode strings are written to a file, they will be converted to byte strings using this encoding. In addition, when the file is connected to a terminal, the attribute gives the encoding that the terminal is likely to use (that information might be incorrect if the user has misconfigured the terminal). The attribute is read-only and may not be present on all file-like objects. It may also be None, in which case the file uses the system default encoding for converting Unicode strings.

Nouveau dans la version 2.3.

file.errors

The Unicode error handler used along with the encoding.

Nouveau dans la version 2.6.

file.mode

The I/O mode for the file. If the file was created using the open() built-in function, this will be the value of the mode parameter. This is a read-only attribute and may not be present on all file-like objects.

file.name

If the file object was created using open(), the name of the file. Otherwise, some string that indicates the source of the file object, of the form <...>. This is a read-only attribute and may not be present on all file-like objects.

file.newlines

If Python was built with universal newlines enabled (the default) this read-only attribute exists, and for files opened in universal newline read mode it keeps track of the types of newlines encountered while reading the file. The values it can take are '\r', '\n', '\r\n', None (unknown, no newlines read yet) or a tuple containing all the newline types seen, to indicate that multiple newline conventions were encountered. For files not opened in universal newlines read mode the value of this attribute will be None.

file.softspace

Boolean that indicates whether a space character needs to be printed before another value when using the print statement. Classes that are trying to simulate a file object should also have a writable softspace attribute, which should be initialized to zero. This will be automatic for most classes implemented in Python (care may be needed for objects that override attribute access); types implemented in C will have to provide a writable softspace attribute.

Note

This attribute is not used to control the print statement, but to allow the implementation of print to keep track of its internal state.

5.10. memoryview type

Nouveau dans la version 2.7.

memoryview objects allow Python code to access the internal data of an object that supports the buffer protocol without copying. Memory is generally interpreted as simple bytes.

class memoryview(obj)

Create a memoryview that references obj. obj must support the buffer protocol. Built-in objects that support the buffer protocol include str and bytearray (but not unicode).

A memoryview has the notion of an element, which is the atomic memory unit handled by the originating object obj. For many simple types such as str and bytearray, an element is a single byte, but other third-party types may expose larger elements.

len(view) returns the total number of elements in the memoryview, view. The itemsize attribute will give you the number of bytes in a single element.

A memoryview supports slicing to expose its data. Taking a single index will return a single element as a str object. Full slicing will result in a subview:

>>> v = memoryview('abcefg')
>>> v[1]
'b'
>>> v[-1]
'g'
>>> v[1:4]
<memory at 0x77ab28>
>>> v[1:4].tobytes()
'bce'

If the object the memoryview is over supports changing its data, the memoryview supports slice assignment:

>>> data = bytearray('abcefg')
>>> v = memoryview(data)
>>> v.readonly
False
>>> v[0] = 'z'
>>> data
bytearray(b'zbcefg')
>>> v[1:4] = '123'
>>> data
bytearray(b'z123fg')
>>> v[2] = 'spam'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: cannot modify size of memoryview object

Notice how the size of the memoryview object cannot be changed.

memoryview has two methods:

tobytes()

Return the data in the buffer as a bytestring (an object of class str).

>>> m = memoryview("abc")
>>> m.tobytes()
'abc'
tolist()

Return the data in the buffer as a list of integers.

>>> memoryview("abc").tolist()
[97, 98, 99]

There are also several readonly attributes available:

format

A string containing the format (in struct module style) for each element in the view. This defaults to 'B', a simple bytestring.

itemsize

The size in bytes of each element of the memoryview.

shape

A tuple of integers the length of ndim giving the shape of the memory as an N-dimensional array.

ndim

An integer indicating how many dimensions of a multi-dimensional array the memory represents.

strides

A tuple of integers the length of ndim giving the size in bytes to access each element for each dimension of the array.

readonly

A bool indicating whether the memory is read only.

5.11. Context Manager Types

Nouveau dans la version 2.5.

Python’s with statement supports the concept of a runtime context defined by a context manager. This is implemented using two separate methods that allow user-defined classes to define a runtime context that is entered before the statement body is executed and exited when the statement ends.

The context management protocol consists of a pair of methods that need to be provided for a context manager object to define a runtime context:

contextmanager.__enter__()

Enter the runtime context and return either this object or another object related to the runtime context. The value returned by this method is bound to the identifier in the as clause of with statements using this context manager.

An example of a context manager that returns itself is a file object. File objects return themselves from __enter__() to allow open() to be used as the context expression in a with statement.

An example of a context manager that returns a related object is the one returned by decimal.localcontext(). These managers set the active decimal context to a copy of the original decimal context and then return the copy. This allows changes to be made to the current decimal context in the body of the with statement without affecting code outside the with statement.

contextmanager.__exit__(exc_type, exc_val, exc_tb)

Exit the runtime context and return a Boolean flag indicating if any exception that occurred should be suppressed. If an exception occurred while executing the body of the with statement, the arguments contain the exception type, value and traceback information. Otherwise, all three arguments are None.

Returning a true value from this method will cause the with statement to suppress the exception and continue execution with the statement immediately following the with statement. Otherwise the exception continues propagating after this method has finished executing. Exceptions that occur during execution of this method will replace any exception that occurred in the body of the with statement.

The exception passed in should never be reraised explicitly - instead, this method should return a false value to indicate that the method completed successfully and does not want to suppress the raised exception. This allows context management code (such as contextlib.nested) to easily detect whether or not an __exit__() method has actually failed.

Python defines several context managers to support easy thread synchronisation, prompt closure of files or other objects, and simpler manipulation of the active decimal arithmetic context. The specific types are not treated specially beyond their implementation of the context management protocol. See the contextlib module for some examples.

Python’s generators and the contextlib.contextmanager decorator provide a convenient way to implement these protocols. If a generator function is decorated with the contextlib.contextmanager decorator, it will return a context manager implementing the necessary __enter__() and __exit__() methods, rather than the iterator produced by an undecorated generator function.

Note that there is no specific slot for any of these methods in the type structure for Python objects in the Python/C API. Extension types wanting to define these methods must provide them as a normal Python accessible method. Compared to the overhead of setting up the runtime context, the overhead of a single class dictionary lookup is negligible.

5.12. Other Built-in Types

The interpreter supports several other kinds of objects. Most of these support only one or two operations.

5.12.1. Modules

The only special operation on a module is attribute access: m.name, where m is a module and name accesses a name defined in m‘s symbol table. Module attributes can be assigned to. (Note that the import statement is not, strictly speaking, an operation on a module object; import foo does not require a module object named foo to exist, rather it requires an (external) definition for a module named foo somewhere.)

A special attribute of every module is __dict__. This is the dictionary containing the module’s symbol table. Modifying this dictionary will actually change the module’s symbol table, but direct assignment to the __dict__ attribute is not possible (you can write m.__dict__['a'] = 1, which defines m.a to be 1, but you can’t write m.__dict__ = {}). Modifying __dict__ directly is not recommended.

Modules built into the interpreter are written like this: <module 'sys' (built-in)>. If loaded from a file, they are written as <module 'os' from '/usr/local/lib/pythonX.Y/os.pyc'>.

5.12.2. Classes and Class Instances

Voir Objects, values and types et Class definitions.

5.12.3. Fonctions

Function objects are created by function definitions. The only operation on a function object is to call it: func(argument-list).

There are really two flavors of function objects: built-in functions and user-defined functions. Both support the same operation (to call the function), but the implementation is different, hence the different object types.

See Function definitions for more information.

5.12.4. Méthodes

Methods are functions that are called using the attribute notation. There are two flavors: built-in methods (such as append() on lists) and class instance methods. Built-in methods are described with the types that support them.

The implementation adds two special read-only attributes to class instance methods: m.im_self is the object on which the method operates, and m.im_func is the function implementing the method. Calling m(arg-1, arg-2, ..., arg-n) is completely equivalent to calling m.im_func(m.im_self, arg-1, arg-2, ..., arg-n).

Class instance methods are either bound or unbound, referring to whether the method was accessed through an instance or a class, respectively. When a method is unbound, its im_self attribute will be None and if called, an explicit self object must be passed as the first argument. In this case, self must be an instance of the unbound method’s class (or a subclass of that class), otherwise a TypeError is raised.

Like function objects, methods objects support getting arbitrary attributes. However, since method attributes are actually stored on the underlying function object (meth.im_func), setting method attributes on either bound or unbound methods is disallowed. Attempting to set an attribute on a method results in an AttributeError being raised. In order to set a method attribute, you need to explicitly set it on the underlying function object:

>>> class C:
...     def method(self):
...         pass
...
>>> c = C()
>>> c.method.whoami = 'my name is method'  # can't set on the method
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'instancemethod' object has no attribute 'whoami'
>>> c.method.im_func.whoami = 'my name is method'
>>> c.method.whoami
'my name is method'

See The standard type hierarchy for more information.

5.12.5. Objets Code

Code objects are used by the implementation to represent “pseudo-compiled” executable Python code such as a function body. They differ from function objects because they don’t contain a reference to their global execution environment. Code objects are returned by the built-in compile() function and can be extracted from function objects through their func_code attribute. See also the code module.

A code object can be executed or evaluated by passing it (instead of a source string) to the exec statement or the built-in eval() function.

See The standard type hierarchy for more information.

5.12.6. Type Objects

Type objects represent the various object types. An object’s type is accessed by the built-in function type(). There are no special operations on types. The standard module types defines names for all standard built-in types.

Types are written like this: <type 'int'>.

5.12.7. The Null Object

This object is returned by functions that don’t explicitly return a value. It supports no special operations. There is exactly one null object, named None (a built-in name).

It is written as None.

5.12.8. The Ellipsis Object

This object is used by extended slice notation (see Slicings). It supports no special operations. There is exactly one ellipsis object, named Ellipsis (a built-in name).

It is written as Ellipsis. When in a subscript, it can also be written as ..., for example seq[...].

5.12.9. The NotImplemented Object

This object is returned from comparisons and binary operations when they are asked to operate on types they don’t support. See Comparaisons for more information.

It is written as NotImplemented.

5.12.10. Boolean Values

Boolean values are the two constant objects False and True. They are used to represent truth values (although other values can also be considered false or true). In numeric contexts (for example when used as the argument to an arithmetic operator), they behave like the integers 0 and 1, respectively. The built-in function bool() can be used to convert any value to a Boolean, if the value can be interpreted as a truth value (see section Valeurs booléennes above).

They are written as False and True, respectively.

5.12.11. Internal Objects

See The standard type hierarchy for this information. It describes stack frame objects, traceback objects, and slice objects.

5.13. Special Attributes

The implementation adds a few special read-only attributes to several object types, where they are relevant. Some of these are not reported by the dir() built-in function.

object.__dict__

A dictionary or other mapping object used to store an object’s (writable) attributes.

object.__methods__

Obsolète depuis la version 2.2: Use the built-in function dir() to get a list of an object’s attributes. This attribute is no longer available.

object.__members__

Obsolète depuis la version 2.2: Use the built-in function dir() to get a list of an object’s attributes. This attribute is no longer available.

instance.__class__

The class to which a class instance belongs.

class.__bases__

The tuple of base classes of a class object.

definition.__name__

The name of the class, type, function, method, descriptor, or generator instance.

The following attributes are only supported by new-style classes.

class.__mro__

This attribute is a tuple of classes that are considered when looking for base classes during method resolution.

class.mro()

This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in __mro__.

class.__subclasses__()

Each new-style class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. Example:

>>> int.__subclasses__()
[<type 'bool'>]

Notes

[1]Additional information on these special methods may be found in the Python Reference Manual (Basic customization).
[2]As a consequence, the list [1, 2] is considered equal to [1.0, 2.0], and similarly for tuples.
[3]They must have since the parser can’t tell the type of the operands.
[4](1, 2, 3, 4) Cased characters are those with general category property being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt” (Letter, titlecase).
[5]To format only a tuple you should therefore provide a singleton tuple whose only element is the tuple to be formatted.
[6]The advantage of leaving the newline on is that returning an empty string is then an unambiguous EOF indication. It is also possible (in cases where it might matter, for example, if you want to make an exact copy of a file while scanning its lines) to tell whether the last line of a file ended in a newline or not (yes this happens!).