# 2. Analyse lexicale

A Python program is read by a parser. Input to the parser is a stream of tokens, generated by the lexical analyzer (also known as the tokenizer). This chapter describes how the lexical analyzer produces these tokens.

The lexical analyzer determines the program text's encoding (UTF-8 by default), and decodes the text into source characters. If the text cannot be decoded, a `SyntaxError` is raised.

Next, the lexical analyzer uses the source characters to generate a stream of tokens. The type of a generated token generally depends on the next source character to be processed. Similarly, other special behavior of the analyzer depends on the first source character that hasn't yet been processed. The following table gives a quick summary of these source characters, with links to sections that contain more information.

Character | Next token (or other relevant documentation)
--- | ---
space tab formfeed | Whitespace
CR, LF | New line Indentation
backslash (`\`) | Explicit line joining (Also significant in string escape sequences)
hash (`#`) | Comment
quote (`'`, `"`) | String literal
ASCII letter (`a`-`z`, `A`-`Z`) non-ASCII character | Name Prefixed string or bytes literal
underscore (`_`) | Name (Can also be part of numeric literals)
number (`0`-`9`) | Numeric literal
dot (`.`) | Numeric literal Operator
question mark (`?`) dollar (`$`) backquote (`​`​`) control character | Error (outside string literals and comments)
other printing character | Operator or delimiter
end of file | End marker

## 2.1. Structure des lignes

Un programme en Python est divisé en lignes logiques.

### 2.1.1. Lignes logiques

The end of a logical line is represented by the token `NEWLINE`. Statements cannot cross logical line boundaries except where `NEWLINE` is allowed by the syntax (e.g., between statements in compound statements). A logical line is constructed from one or more physical lines by following the explicit or implicit line joining rules.

### 2.1.2. Lignes physiques

A physical line is a sequence of characters terminated by one the following end-of-line sequences:

- the Unix form using ASCII LF (linefeed),

- the Windows form using the ASCII sequence CR LF (return followed by linefeed),

- the 'Classic Mac OS' form using the ASCII CR (return) character.

Regardless of platform, each of these sequences is replaced by a single ASCII LF (linefeed) character. (This is done even inside string literals.) Each line can use any of the sequences; they do not need to be consistent within a file.

The end of input also serves as an implicit terminator for the final physical line.

Formally:

    newline: <ASCII LF> | <ASCII CR> <ASCII LF> | <ASCII CR>

### 2.1.3. Commentaires

Un commentaire commence par le caractère croisillon (`#`, hash en anglais et qui ressemble au symbole musical dièse, c'est pourquoi il est souvent improprement appelé caractère dièse) situé en dehors d'une chaine de caractères littérale et se termine à la fin de la ligne physique. Un commentaire signifie la fin de la ligne logique à moins qu'une règle de continuation de ligne implicite ne s'applique. Les commentaires sont ignorés au niveau syntaxique, ce ne sont pas des lexèmes.

### 2.1.4. Déclaration d'encodage

Si un commentaire placé sur la première ou deuxième ligne du script Python correspond à l'expression rationnelle `coding[=:]\s*([-\w.]+)`, ce commentaire est analysé comme une déclaration d'encodage ; le premier groupe de cette expression désigne l'encodage du fichier source. Cette déclaration d'encodage doit être seule sur sa ligne et, si elle est sur la deuxième ligne, la première ligne doit aussi être une ligne composée uniquement d'un commentaire. Les formes recommandées pour l'expression de l'encodage sont

    # -*- coding: <encoding-name> -*-

qui est reconnue aussi par GNU Emacs et

    # vim:fileencoding=<encoding-name>

qui est reconnue par VIM de Bram Moolenaar.

If no encoding declaration is found, the default encoding is UTF-8. If the implicit or explicit encoding of a file is UTF-8, an initial UTF-8 byte-order mark (`b'\xef\xbb\xbf'`) is ignored rather than being a syntax error.

Si un encodage est déclaré, le nom de l'encodage doit être reconnu par Python (voir Standard Encodings). L'encodage est utilisé pour toute l'analyse lexicale, y compris les chaînes de caractères, les commentaires et les identifiants.

All lexical analysis, including string literals, comments and identifiers, works on Unicode text decoded using the source encoding. Any Unicode code point, except the NUL control character, can appear in Python source.

    source_character:  <any Unicode code point, except NUL>

### 2.1.5. Continuation de ligne explicite

Deux lignes physiques, ou plus, peuvent être jointes pour former une seule ligne logique en utilisant la barre oblique inversée (`\`) selon la règle suivante : quand la ligne physique se termine par une barre oblique inversée qui ne fait pas partie d'une chaine de caractères ou d'un commentaire, la ligne immédiatement suivante lui est adjointe pour former une seule ligne logique, en supprimant la barre oblique inversée et le caractère de fin de ligne. Par exemple :

    if 1900 < year < 2100 and 1 <= month <= 12 \
       and 1 <= day <= 31 and 0 <= hour < 24 \
       and 0 <= minute < 60 and 0 <= second < 60:   # Looks like a valid date
            return 1

Une ligne que se termine par une barre oblique inversée ne peut pas avoir de commentaire. La barre oblique inversée ne permet pas de continuer un commentaire. La barre oblique inversée ne permet pas de continuer un lexème, sauf s'il s'agit d'une chaîne de caractères (par exemple, les lexèmes autres que les chaînes de caractères ne peuvent pas être répartis sur plusieurs lignes en utilisant une barre oblique inversée). La barre oblique inversée n'est pas autorisée ailleurs sur la ligne, en dehors d'une chaîne de caractères.

### 2.1.6. Continuation de ligne implicite

Les expressions entre parenthèses, crochets ou accolades peuvent être réparties sur plusieurs lignes sans utiliser de barre oblique inversée. Par exemple :

    month_names = ['Januari', 'Februari', 'Maart',      # These are the
                   'April',   'Mei',      'Juni',       # Dutch names
                   'Juli',    'Augustus', 'September',  # for the months
                   'Oktober', 'November', 'December']   # of the year

Les lignes continuées implicitement peuvent avoir des commentaires. L'indentation des lignes de continuation n'est pas importante. Une ligne blanche est autorisée comme ligne de continuation. Il ne doit pas y avoir de lexème NEWLINE entre des lignes implicitement continuées. Les lignes continuées implicitement peuvent être utilisées dans des chaînes entre triples guillemets (voir ci-dessous) ; dans ce cas, elles ne peuvent pas avoir de commentaires.

### 2.1.7. Lignes vierges

A logical line that contains only spaces, tabs, formfeeds and possibly a comment, is ignored (i.e., no `NEWLINE` token is generated). During interactive input of statements, handling of a blank line may differ depending on the implementation of the read-eval-print loop. In the standard interactive interpreter, an entirely blank logical line (that is, one containing not even whitespace or a comment) terminates a multi-line statement.

### 2.1.8. Indentation

Des espaces ou tabulations au début d’une ligne logique sont utilisées pour connaître le niveau d’indentation de la ligne, qui est ensuite utilisé pour déterminer comment les instructions sont groupées.

Les tabulations sont remplacées (de la gauche vers la droite) par une à huit espaces de manière à ce que le nombre de caractères remplacés soit un multiple de huit (nous avons ainsi la même règle que celle d'Unix). Le nombre total d'espaces précédant le premier caractère non blanc détermine alors le niveau d'indentation de la ligne. L'indentation ne peut pas être répartie sur plusieurs lignes physiques à l'aide de barres obliques inversées ; les espaces jusqu'à la première barre oblique inversée déterminent l'indentation.

L'indentation est déclarée inconsistante et rejetée si, dans un même fichier source, le mélange des tabulations et des espaces est tel que la signification dépend du nombre d'espaces que représente une tabulation. Une exception `TabError` est levée dans ce cas.

Note de compatibilité entre les plateformes : en raison de la nature des éditeurs de texte sur les plateformes non Unix, il n'est pas judicieux d'utiliser un mélange d'espaces et de tabulations pour l'indentation dans un seul fichier source. Il convient également de noter que des plateformes peuvent explicitement limiter le niveau d'indentation maximal.

Un caractère de saut de page peut être présent au début de la ligne ; il est ignoré pour les calculs d'indentation ci-dessus. Les caractères de saut de page se trouvant ailleurs avec les espaces en tête de ligne ont un effet indéfini (par exemple, ils peuvent remettre à zéro le nombre d'espaces).

The indentation levels of consecutive lines are used to generate `INDENT` and `DEDENT` tokens, using a stack, as follows.

Before the first line of the file is read, a single zero is pushed on the stack; this will never be popped off again. The numbers pushed on the stack will always be strictly increasing from bottom to top. At the beginning of each logical line, the line's indentation level is compared to the top of the stack. If it is equal, nothing happens. If it is larger, it is pushed on the stack, and one `INDENT` token is generated. If it is smaller, it must be one of the numbers occurring on the stack; all numbers on the stack that are larger are popped off, and for each number popped off a `DEDENT` token is generated. At the end of the file, a `DEDENT` token is generated for each number remaining on the stack that is larger than zero.

Voici un exemple de code Python correctement indenté (bien que très confus) :

    def perm(l):
            # Compute the list of all permutations of l
        if len(l) <= 1:
                      return [l]
        r = []
        for i in range(len(l)):
                 s = l[:i] + l[i+1:]
                 p = perm(s)
                 for x in p:
                  r.append(l[i:i+1] + x)
        return r

L'exemple suivant montre plusieurs erreurs d'indentation :

     def perm(l):                       # error: first line indented
    for i in range(len(l)):             # error: not indented
        s = l[:i] + l[i+1:]
            p = perm(l[:i] + l[i+1:])   # error: unexpected indent
            for x in p:
                    r.append(l[i:i+1] + x)
                return r                # error: inconsistent dedent

En fait, les trois premières erreurs sont détectées par l'analyseur syntaxique ; seule la dernière erreur est trouvée par l'analyseur lexical (l'indentation de `return r` ne correspond à aucun niveau dans la pile).

### 2.1.9. Espaces entre lexèmes

Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens. Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token. For example, `ab` is one token, but `a b` is two tokens. However, `+a` and `+ a` both produce two tokens, `+` and `a`, as `+a` is not a valid token.

### 2.1.10. End marker

At the end of non-interactive input, the lexical analyzer generates an `ENDMARKER` token.

## 2.2. Autres lexèmes

Besides `NEWLINE`, `INDENT` and `DEDENT`, the following categories of tokens exist: identifiers and keywords (`NAME`), literals (such as `NUMBER` and `STRING`), and other symbols (operators and delimiters, `OP`). Whitespace characters (other than logical line terminators, discussed earlier) are not tokens, but serve to delimit tokens. Where ambiguity exists, a token comprises the longest possible string that forms a legal token, when read from left to right.

## 2.3. Names (identifiers and keywords)

`NAME` tokens represent identifiers, keywords, and soft keywords.

Within the ASCII range (U+0001..U+007F), the valid characters for names include the uppercase and lowercase letters (`A-Z` and `a-z`), the underscore `_` and, except for the first character, the digits `0` through `9`.

Names must contain at least one character, but have no upper length limit. Case is significant.

Besides `A-Z`, `a-z`, `_` and `0-9`, names can also use "letter-like" and "number-like" characters from outside the ASCII range, as detailed below.

All identifiers are converted into the normalization form NFKC while parsing; comparison of identifiers is based on NFKC.

Formally, the first character of a normalized identifier must belong to the set `id_start`, which is the union of:

- Unicode category `<Lu>` - uppercase letters (includes `A` to `Z`)

- Unicode category `<Ll>` - lowercase letters (includes `a` to `z`)

- Unicode category `<Lt>` - titlecase letters

- Unicode category `<Lm>` - modifier letters

- Unicode category `<Lo>` - other letters

- Unicode category `<Nl>` - letter numbers

- {`"_"`} - the underscore

- `<Other_ID_Start>` - an explicit set of characters in PropList.txt to support backwards compatibility

The remaining characters must belong to the set `id_continue`, which is the union of:

- all characters in `id_start`

- Unicode category `<Nd>` - decimal numbers (includes `0` to `9`)

- Unicode category `<Pc>` - connector punctuations

- Unicode category `<Mn>` - nonspacing marks

- Unicode category `<Mc>` - spacing combining marks

- `<Other_ID_Continue>` - another explicit set of characters in PropList.txt to support backwards compatibility

Unicode categories use the version of the Unicode Character Database as included in the `unicodedata` module.

These sets are based on the Unicode standard annex UAX-31. See also PEP 3131 for further details.

Even more formally, names are described by the following lexical definitions:

    NAME:         xid_start xid_continue*
    id_start:     <Lu> | <Ll> | <Lt> | <Lm> | <Lo> | <Nl> | "_" | <Other_ID_Start>
    id_continue:  id_start | <Nd> | <Pc> | <Mn> | <Mc> | <Other_ID_Continue>
    xid_start:    <all characters in id_start whose NFKC normalization is
                   in (id_start xid_continue*)">
    xid_continue: <all characters in id_continue whose NFKC normalization is
                   in (id_continue*)">
    identifier:   <NAME, except keywords>

A non-normative listing of all valid identifier characters as defined by Unicode is available in the DerivedCoreProperties.txt file in the Unicode Character Database.

### 2.3.1. Mots-clés

The following names are used as reserved words, or keywords of the language, and cannot be used as ordinary identifiers. They must be spelled exactly as written here:

    False      await      else       import     pass
    None       break      except     in         raise
    True       class      finally    is         return
    and        continue   for        lambda     try
    as         def        from       nonlocal   while
    assert     del        global     not        with
    async      elif       if         or         yield

### 2.3.2. Mots-clés ad hoc

Ajouté dans la version 3.10.

Some names are only reserved under specific contexts. These are known as soft keywords:

- `match`, `case`, and `_`, when used in the `match` statement.

- `type`, when used in the `type` statement.

These syntactically act as keywords in their specific contexts, but this distinction is done at the parser level, not when tokenizing.

As soft keywords, their use in the grammar is possible while still preserving compatibility with existing code that uses these names as identifier names.

Modifié dans la version 3.12: `type` is now a soft keyword.

### 2.3.3. Classes réservées pour les identifiants

Certaines classes d'identifiants (outre les mots-clés) ont une signification particulière. Ces classes se reconnaissent par des caractères de soulignement en tête et en queue d'identifiant :

`_*`

  N'est pas importé par `from module import *`.

`_`

  Dans un motif `case` d'une instruction `match`, `_` est un mot-clé ad hoc qui décrit un motif attrape-tout.

  De son côté, l'interpréteur interactif place le résultat de la dernière évaluation dans la variable `-` (son emplacement se situe dans le module `builtins`, avec les fonctions natives telles que `print`).

  Ailleurs, `_` est un identifiant comme un autre. Il est souvent utilisé pour désigner des éléments « spéciaux », mais il n'est pas spécial pour Python en tant que tel.

  Note

  Le nom `_` est souvent utilisé pour internationaliser l'affichage ; reportez-vous à la documentation du module `gettext` pour plus d'informations sur cette convention.

  Il est aussi communément utilisé pour signifier que la variable n'est pas utilisée.

`__*__`

  Noms définis par le système, appelés noms « dunder » (pour Double Underscores) de manière informelle. Ces noms sont définis par l'interpréteur et son implémentation (y compris la bibliothèque standard). Les noms actuels définis par le système sont abordés dans la section Méthodes spéciales, mais aussi ailleurs. D'autres noms seront probablement définis dans les futures versions de Python. Toute utilisation de noms de la forme `__*__`, dans n'importe quel contexte, qui n'est pas conforme à ce qu'indique explicitement la documentation, est sujette à des mauvaises surprises sans avertissement.

`__*`

  Noms privés pour une classe. Les noms de cette forme, lorsqu'ils sont utilisés dans le contexte d'une définition de classe, sont réécrits sous une forme modifiée pour éviter les conflits de noms entre les attributs « privés » des classes de base et les classes dérivées. Voir la section Identifiants (noms).

## 2.4. Littéraux

Les littéraux sont des notations pour indiquer des valeurs constantes de certains types natifs.

In terms of lexical analysis, Python has string, bytes and numeric literals.

Other "literals" are lexically denoted using keywords (`None`, `True`, `False`) and the special ellipsis token (`...`).

## 2.5. Littéraux de chaînes de caractères et de suites d'octets

String literals are text enclosed in single quotes (`'`) or double quotes (`"`). For example:

    "spam"
    'eggs'

The quote used to start the literal also terminates it, so a string literal can only contain the other quote (except with escape sequences, see below). For example:

    'Say "Hello", please.'
    "Don't do that!"

Except for this limitation, the choice of quote character (`'` or `"`) does not affect how the literal is parsed.

Inside a string literal, the backslash (`\`) character introduces an escape sequence, which has special meaning depending on the character after the backslash. For example, `\"` denotes the double quote character, and does not end the string:

    >>> print("Say \"Hello\" to everyone!")
    Say "Hello" to everyone!

See escape sequences below for a full list of such sequences, and more details.

### 2.5.1. Triple-quoted strings

Strings can also be enclosed in matching groups of three single or double quotes. These are generally referred to as triple-quoted strings:

    """This is a triple-quoted string."""

In triple-quoted literals, unescaped quotes are allowed (and are retained), except that three unescaped quotes in a row terminate the literal, if they are of the same kind (`'` or `"`) used at the start:

    """This string has "quotes" inside."""

Unescaped newlines are also allowed and retained:

    '''This triple-quoted string
    continues on the next line.'''

### 2.5.2. String prefixes

String literals can have an optional prefix that influences how the content of the literal is parsed, for example:

    b"data"
    f'{result=}'

The allowed prefixes are:

- `b`: Bytes literal

- `r`: Raw string

- `f`: Formatted string literal ("f-string")

- `t`: Template string literal ("t-string")

- `u`: No effect (allowed for backwards compatibility)

See the linked sections for details on each type.

Prefixes are case-insensitive (for example, '`B`' works the same as '`b`'). The '`r`' prefix can be combined with '`f`', '`t`' or '`b`', so '`fr`', '`rf`', '`tr`', '`rt`', '`br`', and '`rb`' are also valid prefixes.

Ajouté dans la version 3.3: le préfixe `'rb'` a été ajouté comme synonyme de `'br'` pour les littéraux de suites d'octets.

la gestion du préfixe historique pour les chaînes Unicode (`u'chaine'`) a été réintroduite afin de simplifier la maintenance de code compatible Python 2.x et 3.x. Voir la PEP 414 pour davantage d'informations.

### 2.5.3. Formal grammar

String literals, except "f-strings" and "t-strings", are described by the following lexical definitions.

These definitions use negative lookaheads (`!`) to indicate that an ending quote ends the literal.

    STRING:          [stringprefix] (stringcontent)
    stringprefix:    <("r" | "u" | "b" | "br" | "rb"), case-insensitive>
    stringcontent:
       | "'''" ( !"'''" longstringitem)* "'''"
       | '"""' ( !'"""' longstringitem)* '"""'
       | "'" ( !"'" stringitem)* "'"
       | '"' ( !'"' stringitem)* '"'
    stringitem:      stringchar | stringescapeseq
    stringchar:      <any source_character, except backslash and newline>
    longstringitem:  stringitem | newline
    stringescapeseq: "\" <any source_character>

Note that as in all lexical definitions, whitespace is significant. In particular, the prefix (if any) must be immediately followed by the starting quote.

### 2.5.4. Escape sequences

Unless an '`r`' or '`R`' prefix is present, escape sequences in string and bytes literals are interpreted according to rules similar to those used by Standard C. The recognized escape sequences are:

Séquence d'échappement | Signification
--- | ---
`\`<newline> | Ignored end of line
`\\` | Backslash
`\'` | Single quote
`\"` | Double quote
`\a` | cloche ASCII (BEL)
`\b` | retour arrière ASCII (BS)
`\f` | saut de page ASCII (FF)
`\n` | saut de ligne ASCII (LF)
`\r` | retour à la ligne ASCII (CR)
`\t` | tabulation horizontale ASCII (TAB)
`\v` | tabulation verticale ASCII (VT)
`\ooo` | Octal character
`\xhh` | Hexadecimal character
`\N{name}` | Named Unicode character
`\uxxxx` | Hexadecimal Unicode character
`\Uxxxxxxxx` | Hexadecimal Unicode character

#### 2.5.4.1. Ignored end of line

A backslash can be added at the end of a line to ignore the newline:

    >>> 'This string will not include \
    ... backslashes or newline characters.'
    'This string will not include backslashes or newline characters.'

The same result can be achieved using triple-quoted strings, or parentheses and string literal concatenation.

#### 2.5.4.2. Escaped characters

To include a backslash in a non-raw Python string literal, it must be doubled. The `\\` escape sequence denotes a single backslash character:

    >>> print('C:\\Program Files')
    C:\Program Files

Similarly, the `\'` and `\"` sequences denote the single and double quote character, respectively:

    >>> print('\' and \"')
    ' and "

#### 2.5.4.3. Octal character

The sequence `\ooo` denotes a character with the octal (base 8) value ooo:

    >>> '\120'
    'P'

Up to three octal digits (0 through 7) are accepted.

In a bytes literal, character means a byte with the given value. In a string literal, it means a Unicode character with the given value.

Modifié dans la version 3.11: Octal escapes with value larger than `0o377` (255) produce a `DeprecationWarning`.

Modifié dans la version 3.12: Octal escapes with value larger than `0o377` (255) produce a `SyntaxWarning`. In a future Python version they will raise a `SyntaxError`.

#### 2.5.4.4. Hexadecimal character

The sequence `\xhh` denotes a character with the hex (base 16) value hh:

    >>> '\x50'
    'P'

Contrairement au C Standard, il est obligatoire de fournir deux chiffres hexadécimaux.

In a bytes literal, character means a byte with the given value. In a string literal, it means a Unicode character with the given value.

#### 2.5.4.5. Named Unicode character

The sequence `\N{name}` denotes a Unicode character with the given name:

    >>> '\N{LATIN CAPITAL LETTER P}'
    'P'
    >>> '\N{SNAKE}'
    '🐍'

This sequence cannot appear in bytes literals.

Modifié dans la version 3.3: Support for name aliases has been added.

#### 2.5.4.6. Hexadecimal Unicode characters

These sequences `\uxxxx` and `\Uxxxxxxxx` denote the Unicode character with the given hex (base 16) value. Exactly four digits are required for `\u`; exactly eight digits are required for `\U`. The latter can encode any Unicode character.

    >>> '\u1234'
    'ሴ'
    >>> '\U0001f40d'
    '🐍'

These sequences cannot appear in bytes literals.

#### 2.5.4.7. Unrecognized escape sequences

Unlike in Standard C, all unrecognized escape sequences are left in the string unchanged, that is, the backslash is left in the result:

    >>> print('\q')
    \q
    >>> list('\q')
    ['\\', 'q']

Note that for bytes literals, the escape sequences only recognized in string literals (`\N...`, `\u...`, `\U...`) fall into the category of unrecognized escapes.

Modifié dans la version 3.6: Unrecognized escape sequences produce a `DeprecationWarning`.

Modifié dans la version 3.12: Unrecognized escape sequences produce a `SyntaxWarning`. In a future Python version they will raise a `SyntaxError`.

### 2.5.5. Bytes literals

Bytes literals are always prefixed with '`b`' or '`B`'; they produce an instance of the `bytes` type instead of the `str` type. They may only contain ASCII characters; bytes with a numeric value of 128 or greater must be expressed with escape sequences (typically Hexadecimal character or Octal character):

    >>> b'\x89PNG\r\n\x1a\n'
    b'\x89PNG\r\n\x1a\n'
    >>> list(b'\x89PNG\r\n\x1a\n')
    [137, 80, 78, 71, 13, 10, 26, 10]

Similarly, a zero byte must be expressed using an escape sequence (typically `\0` or `\x00`).

### 2.5.6. Raw string literals

Both string and bytes literals may optionally be prefixed with a letter '`r`' or '`R`'; such constructs are called raw string literals and raw bytes literals respectively and treat backslashes as literal characters. As a result, in raw string literals, escape sequences are not treated specially:

    >>> r'\d{4}-\d{2}-\d{2}'
    '\\d{4}-\\d{2}-\\d{2}'

Même dans une chaîne littérale brute, les guillemets peuvent être échappés avec une barre oblique inversée mais la barre oblique inversée reste dans le résultat ; par exemple, `r"\""` est une chaîne de caractères valide composée de deux caractères : une barre oblique inversée et un guillemet double ; `r"\"` n'est pas une chaîne de caractères valide (même une chaîne de caractères brute ne peut pas se terminer par un nombre impair de barres obliques inversées). Plus précisément, une chaîne littérale brute ne peut pas se terminer par une seule barre oblique inversée (puisque la barre oblique inversée échappe le guillemet suivant). Notez également qu'une simple barre oblique inversée suivie d'un saut de ligne est interprétée comme deux caractères faisant partie du littéral et non comme une continuation de ligne.

### 2.5.7. f-strings

Ajouté dans la version 3.6.

A formatted string literal or f-string is a string literal that is prefixed with '`f`' or '`F`'. These strings may contain replacement fields, which are expressions delimited by curly braces `{}`. While other string literals always have a constant value, formatted strings are really expressions evaluated at run time.

Les séquences d'échappement sont décodées comme à l'intérieur des chaînes de caractères ordinaires (sauf lorsqu'une chaîne de caractères est également marquée comme une chaîne brute). Après décodage, la grammaire s'appliquant au contenu de la chaîne de caractères est :

    f_string:          (literal_char | "{{" | "}}" | replacement_field)*
    replacement_field: "{" f_expression ["="] ["!" conversion] [":" format_spec] "}"
    f_expression:      (conditional_expression | "*" or_expr)
                         ("," conditional_expression | "," "*" or_expr)* [","]
                       | yield_expression
    conversion:        "s" | "r" | "a"
    format_spec:       (literal_char | replacement_field)*
    literal_char:      <any code point except "{", "}" or NULL>

Les portions qui sont en dehors des accolades sont traitées comme les littéraux, sauf les doubles accolades `'{{'` ou `'}}'` qui sont remplacées par la simple accolade correspondante. Une simple accolade ouvrante `'{'` marque le début du champ à remplacer, qui commence par une expression Python. Pour afficher à la fois le texte de l'expression et sa valeur une fois évaluée (utile lors du débogage), un signe égal `'='` peut être ajouté après l'expression. Ensuite, il peut y avoir un champ de conversion, introduit par un point d'exclamation `'!'`. Une spécification de format peut aussi être rajoutée, introduite par le caractère deux-points `':'`. Le champ à remplacer se termine par une accolade fermante `'}'`.

Expressions in formatted string literals are treated like regular Python expressions surrounded by parentheses, with a few exceptions. An empty expression is not allowed, and both `lambda` and assignment expressions `:=` must be surrounded by explicit parentheses. Each expression is evaluated in the context where the formatted string literal appears, in order from left to right. Replacement expressions can contain newlines in both single-quoted and triple-quoted f-strings and they can contain comments. Everything that comes after a `#` inside a replacement field is a comment (even closing braces and quotes). In that case, replacement fields must be closed in a different line.

    >>> f"abc{a # This is a comment }"
    ... + 3}"
    'abc5'

Modifié dans la version 3.7: Avant Python 3.7, il était illégal d’utiliser `await` ainsi que les compréhensions utilisant `async for` dans les expressions au sein des chaînes de caractères formatées littérales à cause d’un problème dans l’implémentation.

Modifié dans la version 3.12: Prior to Python 3.12, comments were not allowed inside f-string replacement fields.

Lorsqu'un signe égal `'='` est présent, la sortie comprend le texte de l'expression, le signe `'='` et la valeur calculée. Les espaces après l'accolade ouvrante `'{'`, dans l'expression et après le signe `'='` sont conservées à l'affichage. Par défaut, le signe `'='` utilise la `repr()` de l'expression, sauf si un format est indiqué. Quand le format est indiqué, c'est `str()` de l'expression qui est utilisée à moins qu'une conversion `!r` ne soit déclarée.

Ajouté dans la version 3.8: le signe égal `'='`.

Si une conversion est spécifiée, le résultat de l'évaluation de l'expression est converti avant d'être formaté. La conversion `'!s'` appelle `str()` sur le résultat, `'!r'` appelle `repr()` et `'!a'` appelle `ascii()`.

The result is then formatted using the `format()` protocol. The format specifier is passed to the `__format__()` method of the expression or conversion result. An empty string is passed when the format specifier is omitted. The formatted result is then included in the final value of the whole string.

Top-level format specifiers may include nested replacement fields. These nested fields may include their own conversion fields and format specifiers, but may not include more deeply nested replacement fields. The format specifier mini-language is the same as that used by the `str.format()` method.

Les chaînes formatées littérales peuvent être concaténées mais les champs à remplacer ne peuvent pas être divisés entre les littéraux.

Quelques exemples de chaines formatées littérales :

    >>> name = "Fred"
    >>> f"He said his name is {name!r}."
    "He said his name is 'Fred'."
    >>> f"He said his name is {repr(name)}."  # repr() is equivalent to !r
    "He said his name is 'Fred'."
    >>> width = 10
    >>> precision = 4
    >>> value = decimal.Decimal("12.34567")
    >>> f"result: {value:{width}.{precision}}"  # nested fields
    'result:      12.35'
    >>> today = datetime(year=2017, month=1, day=27)
    >>> f"{today:%B %d, %Y}"  # using date format specifier
    'January 27, 2017'
    >>> f"{today=:%B %d, %Y}" # using date format specifier and debugging
    'today=January 27, 2017'
    >>> number = 1024
    >>> f"{number:#0x}"  # using integer format specifier
    '0x400'
    >>> foo = "bar"
    >>> f"{ foo = }" # preserves whitespace
    " foo = 'bar'"
    >>> line = "The mill's closed"
    >>> f"{line = }"
    'line = "The mill\'s closed"'
    >>> f"{line = :20}"
    "line = The mill's closed   "
    >>> f"{line = !r:20}"
    'line = "The mill\'s closed" '

Reusing the outer f-string quoting type inside a replacement field is permitted:

    >>> a = dict(x=2)
    >>> f"abc {a["x"]} def"
    'abc 2 def'

Modifié dans la version 3.12: Prior to Python 3.12, reuse of the same quoting type of the outer f-string inside a replacement field was not possible.

Backslashes are also allowed in replacement fields and are evaluated the same way as in any other context:

    >>> a = ["a", "b", "c"]
    >>> print(f"List a contains:\n{"\n".join(a)}")
    List a contains:
    a
    b
    c

Modifié dans la version 3.12: Prior to Python 3.12, backslashes were not permitted inside an f-string replacement field.

Une chaine formatée littérale ne peut pas être utilisée en tant que docstring, même si elle ne comporte pas d'expression.

    >>> def foo():
    ...     f"Not a docstring"
    ...
    >>> foo.__doc__ is None
    True

Consultez aussi la PEP 498 qui propose l'ajout des chaines formatées littérales et `str.format()` qui utilise un mécanisme similaire pour formater les chaînes de caractères.

### 2.5.8. t-strings

Ajouté dans la version 3.14.

A template string literal or t-string is a string literal that is prefixed with '`t`' or '`T`'. These strings follow the same syntax and evaluation rules as formatted string literals, with the following differences:

- Rather than evaluating to a `str` object, template string literals evaluate to a `string.templatelib.Template` object.

- The `format()` protocol is not used. Instead, the format specifier and conversions (if any) are passed to a new `Interpolation` object that is created for each evaluated expression. It is up to code that processes the resulting `Template` object to decide how to handle format specifiers and conversions.

- Format specifiers containing nested replacement fields are evaluated eagerly, prior to being passed to the `Interpolation` object. For instance, an interpolation of the form `{amount:.{precision}f}` will evaluate the inner expression `{precision}` to determine the value of the `format_spec` attribute. If `precision` were to be `2`, the resulting format specifier would be `'.2f'`.

- When the equals sign `'='` is provided in an interpolation expression, the text of the expression is appended to the literal string that precedes the relevant interpolation. This includes the equals sign and any surrounding whitespace. The `Interpolation` instance for the expression will be created as normal, except that `conversion` will be set to '`r`' (`repr()`) by default. If an explicit conversion or format specifier are provided, this will override the default behaviour.

## 2.6. Littéraux numériques

`NUMBER` tokens represent numeric literals, of which there are three types: integers, floating-point numbers, and imaginary numbers.

    NUMBER: integer | floatnumber | imagnumber

The numeric value of a numeric literal is the same as if it were passed as a string to the `int`, `float` or `complex` class constructor, respectively. Note that not all valid inputs for those constructors are also valid literals.

Numeric literals do not include a sign; a phrase like `-1` is actually an expression composed of the unary operator '`-`' and the literal `1`.

### 2.6.1. Entiers littéraux

Integer literals denote whole numbers. For example:

    7
    3
    2147483647

There is no limit for the length of integer literals apart from what can be stored in available memory:

    7922816251426433759354395033679228162514264337593543950336

Underscores can be used to group digits for enhanced readability, and are ignored for determining the numeric value of the literal. For example, the following literals are equivalent:

    100_000_000_000
    100000000000
    1_00_00_00_00_000

Underscores can only occur between digits. For example, `_123`, `321_`, and `123__321` are not valid literals.

Integers can be specified in binary (base 2), octal (base 8), or hexadecimal (base 16) using the prefixes `0b`, `0o` and `0x`, respectively. Hexadecimal digits 10 through 15 are represented by letters `A`-`F`, case-insensitive. For example:

    0b100110111
    0b_1110_0101
    0o177
    0o377
    0xdeadbeef
    0xDead_Beef

An underscore can follow the base specifier. For example, `0x_1f` is a valid literal, but `0_x1f` and `0x__1f` are not.

Leading zeros in a non-zero decimal number are not allowed. For example, `0123` is not a valid literal. This is for disambiguation with C-style octal literals, which Python used before version 3.0.

Formally, integer literals are described by the following lexical definitions:

    integer:      decinteger | bininteger | octinteger | hexinteger | zerointeger
    decinteger:   nonzerodigit (["_"] digit)*
    bininteger:   "0" ("b" | "B") (["_"] bindigit)+
    octinteger:   "0" ("o" | "O") (["_"] octdigit)+
    hexinteger:   "0" ("x" | "X") (["_"] hexdigit)+
    zerointeger:  "0"+ (["_"] "0")*
    nonzerodigit: "1"..."9"
    digit:        "0"..."9"
    bindigit:     "0" | "1"
    octdigit:     "0"..."7"
    hexdigit:     digit | "a"..."f" | "A"..."F"

Modifié dans la version 3.6: Les tirets bas ne sont pas autorisés pour grouper les littéraux.

### 2.6.2. Floating-point literals

Floating-point (float) literals, such as `3.14` or `1.5`, denote approximations of real numbers.

They consist of integer and fraction parts, each composed of decimal digits. The parts are separated by a decimal point, `.`:

    2.71828
    4.0

Unlike in integer literals, leading zeros are allowed in the numeric parts. For example, `077.010` is legal, and denotes the same number as `77.10`.

As in integer literals, single underscores may occur between digits to help readability:

    96_485.332_123
    3.14_15_93

Either of these parts, but not both, can be empty. For example:

    10.  # (equivalent to 10.0)
    .001  # (equivalent to 0.001)

Optionally, the integer and fraction may be followed by an exponent: the letter `e` or `E`, followed by an optional sign, `+` or `-`, and a number in the same format as the integer and fraction parts. The `e` or `E` represents "times ten raised to the power of":

    1.0e3  # (represents 1.0×10³, or 1000.0)
    1.166e-5  # (represents 1.166×10⁻⁵, or 0.00001166)
    6.02214076e+23  # (represents 6.02214076×10²³, or 602214076000000000000000.)

In floats with only integer and exponent parts, the decimal point may be omitted:

    1e3  # (equivalent to 1.e3 and 1.0e3)
    0e0  # (equivalent to 0.)

Formally, floating-point literals are described by the following lexical definitions:

    floatnumber:
       | digitpart "." [digitpart] [exponent]
       | "." digitpart [exponent]
       | digitpart exponent
    digitpart: digit (["_"] digit)*
    exponent:  ("e" | "E") ["+" | "-"] digitpart

Modifié dans la version 3.6: Les tirets bas ne sont pas autorisés pour grouper les littéraux.

### 2.6.3. Imaginaires littéraux

Python has complex number objects, but no complex literals. Instead, imaginary literals denote complex numbers with a zero real part.

For example, in math, the complex number 3+4.2i is written as the real number 3 added to the imaginary number 4.2i. Python uses a similar syntax, except the imaginary unit is written as `j` rather than i:

    3+4.2j

This is an expression composed of the integer literal `3`, the operator '`+`', and the imaginary literal `4.2j`. Since these are three separate tokens, whitespace is allowed between them:

    3 + 4.2j

No whitespace is allowed within each token. In particular, the `j` suffix, may not be separated from the number before it.

The number before the `j` has the same syntax as a floating-point literal. Thus, the following are valid imaginary literals:

    4.2j
    3.14j
    10.j
    .001j
    1e100j
    3.14e-10j
    3.14_15_93j

Unlike in a floating-point literal the decimal point can be omitted if the imaginary number only has an integer part. The number is still evaluated as a floating-point number, not an integer:

    10j
    0j
    1000000000000000000000000j   # equivalent to 1e+24j

The `j` suffix is case-insensitive. That means you can use `J` instead:

    3.14J   # equivalent to 3.14j

Formally, imaginary literals are described by the following lexical definition:

    imagnumber: (floatnumber | digitpart) ("j" | "J")

## 2.7. Operators and delimiters

The following grammar defines operator and delimiter tokens, that is, the generic `OP` token type. A list of these tokens and their names is also available in the `token` module documentation.

    OP:
       | assignment_operator
       | bitwise_operator
       | comparison_operator
       | enclosing_delimiter
       | other_delimiter
       | arithmetic_operator
       | "..."
       | other_op

    assignment_operator:   "+=" | "-=" | "*=" | "**=" | "/="  | "//=" | "%=" |
                           "&=" | "|=" | "^=" | "<<=" | ">>=" | "@="  | ":="
    bitwise_operator:      "&"  | "|"  | "^"  | "~"   | "<<"  | ">>"
    comparison_operator:   "<=" | ">=" | "<"  | ">"   | "=="  | "!="
    enclosing_delimiter:   "("  | ")"  | "["  | "]"   | "{"   | "}"
    other_delimiter:       ","  | ":"  | "!"  | ";"   | "="   | "->"
    arithmetic_operator:   "+"  | "-"  | "**" | "*"   | "//"  | "/"   | "%"
    other_op:              "."  | "@"

Note

Generally, operators are used to combine expressions, while delimiters serve other purposes. However, there is no clear, formal distinction between the two categories.

Some tokens can serve as either operators or delimiters, depending on usage. For example, `*` is both the multiplication operator and a delimiter used for sequence unpacking, and `@` is both the matrix multiplication and a delimiter that introduces decorators.

For some tokens, the distinction is unclear. For example, some people consider `.`, `(`, and `)` to be delimiters, while others see the `getattr()` operator and the function call operator(s).

Some of Python's operators, like `and`, `or`, and `not in`, use keyword tokens rather than "symbols" (operator tokens).

A sequence of three consecutive periods (`...`) has a special meaning as an `Ellipsis` literal.