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)       |
|====================================================|====================================================|
| * espace  * 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     | * Name  * Prefixed string or bytes literal         |
| character                                          |                                                    |
+----------------------------------------------------+----------------------------------------------------+
| * underscore ("_")                                 | * Name  * (Can also be part of numeric literals)   |
+----------------------------------------------------+----------------------------------------------------+
| * number ("0"-"9")                                 | * Numeric literal                                  |
+----------------------------------------------------+----------------------------------------------------+
| * dot (".")                                        | * Numeric literal  * Operator                      |
+----------------------------------------------------+----------------------------------------------------+
| * question mark ("?")  * dollar ("$")  * backquote | * Error (outside string literals and comments)     |
| ("​`​")  * control character                       |                                                    |
+----------------------------------------------------+----------------------------------------------------+
| * 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                                    |
+----------------------------------------------------+----------------------------------------------------+
| "\x*hh*"                                           | Hexadecimal character                              |
+----------------------------------------------------+----------------------------------------------------+
| "\N{*name*}"                                       | Named Unicode character                            |
+----------------------------------------------------+----------------------------------------------------+
| "\u*xxxx*"                                         | Hexadecimal Unicode character                      |
+----------------------------------------------------+----------------------------------------------------+
| "\U*xxxxxxxx*"                                     | 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 "\x*hh*" 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 "\u*xxxx*" and "\U*xxxxxxxx*" 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. For example,
"077.010" is legal, and denotes the same number as "77.01".

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+4.2*i* is written as the
real number 3 added to the imaginary number 4.2*i*. 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.
