"struct" --- Interpret bytes as packed binary data
**************************************************

**Code source :** Lib/struct.py

======================================================================

This module converts between Python values and C structs represented
as Python "bytes" objects.  Compact format strings describe the
intended conversions to/from Python values. The module's functions and
objects can be used for two largely distinct applications, data
exchange with external sources (files or network connections), or data
transfer between the Python application and the C layer.

Note:

  When no prefix character is given, native mode is the default. It
  packs or unpacks data based on the platform and compiler on which
  the Python interpreter was built. The result of packing a given C
  struct includes pad bytes which maintain proper alignment for the C
  types involved; similarly, alignment is taken into account when
  unpacking.  In contrast, when communicating data between external
  sources, the programmer is responsible for defining byte ordering
  and padding between elements. See Boutisme, taille et alignement for
  details.

Several "struct" functions (and methods of "Struct") take a *buffer*
argument.  This refers to objects that implement the Protocole tampon
and provide either a readable or read-writable buffer.  The most
common types used for that purpose are "bytes" and "bytearray", but
many other types that can be viewed as an array of bytes implement the
buffer protocol, so that they can be read/filled without additional
copying from a "bytes" object.


Fonctions et exceptions
=======================

Le module définit les exceptions et fonctions suivantes :

exception struct.error

   Exception levée à plusieurs occasions ; l'argument est une chaîne
   qui décrit ce qui ne va pas.

struct.pack(format, v1, v2, ...)

   Renvoie un objet *bytes* contenant les valeurs *v1*, *v2*… agrégées
   conformément à la chaîne de format *format*. Les arguments doivent
   correspondre exactement aux valeurs requises par le format.

struct.pack_into(format, buffer, offset, v1, v2, ...)

   Pack the values *v1*, *v2*, ... according to the format string
   *format* and write the packed bytes into the writable buffer
   *buffer* starting at position *offset*.  Note that *offset* is a
   required argument. A negative *offset* counts from the end of
   *buffer*.

struct.unpack(format, buffer)

   Dissocie depuis le tampon *buffer* (en supposant que celui-ci a été
   agrégé avec "pack(format, …)") à l'aide de la chaîne de format
   *format*. Le résultat est un *n*-uplet, qui peut éventuellement ne
   contenir qu'un seul élément. La taille de *buffer* en octets doit
   correspondre à la taille requise par le format, telle que calculée
   par "calcsize()".

struct.unpack_from(format, /, buffer, offset=0)

   Unpack from *buffer* starting at position *offset*, according to
   the format string *format*.  The result is a tuple even if it
   contains exactly one item.  The buffer's size in bytes, starting at
   position *offset*, must be at least the size required by the
   format, as reflected by "calcsize()". A negative *offset* counts
   from the end of *buffer*.

struct.iter_unpack(format, buffer)

   Iteratively unpack from the buffer *buffer* according to the format
   string *format*.  This function returns an iterator which will read
   equally sized chunks from the buffer until all its contents have
   been consumed.  The buffer's size in bytes must be a multiple of
   the size required by the format, as reflected by "calcsize()".

   Chaque itération produit un *n*-uplet tel que spécifié par la
   chaîne de format.

   Ajouté dans la version 3.4.

struct.calcsize(format)

   Renvoie la taille de la structure (et donc celle de l'objet *bytes*
   produit par "pack(format, ...)") correspondant à la chaîne de
   format *format*.


Chaînes de spécification du format
==================================

Format strings describe the data layout when packing and unpacking
data.  They are built up from format characters, which specify the
type of data being packed/unpacked.  In addition, special characters
control the byte order, size and alignment. Each format string
consists of an optional prefix character which describes the overall
properties of the data and one or more format characters which
describe the actual data values and padding.


Boutisme, taille et alignement
------------------------------

By default, C types are represented in the machine's native format and
byte order, and properly aligned by skipping pad bytes if necessary
(according to the rules used by the C compiler). This behavior is
chosen so that the bytes of a packed struct correspond exactly to the
memory layout of the corresponding C struct. Whether to use native
byte ordering and padding or standard formats depends on the
application.

Cependant, le premier caractère de la chaîne de format peut être
utilisé pour indiquer le boutisme, la taille et l'alignement des
données agrégées, conformément à la table suivante :

+-------------+--------------------------+------------+-------------+
| Caractère   | Boutisme                 | Taille     | Alignement  |
|=============|==========================|============|=============|
| "@"         | natif                    | natif      | natif       |
+-------------+--------------------------+------------+-------------+
| "="         | natif                    | standard   | aucun       |
+-------------+--------------------------+------------+-------------+
| "<"         | petit-boutiste           | standard   | aucun       |
+-------------+--------------------------+------------+-------------+
| ">"         | gros-boutiste            | standard   | aucun       |
+-------------+--------------------------+------------+-------------+
| "!"         | réseau (= gros-boutiste) | standard   | aucun       |
+-------------+--------------------------+------------+-------------+

Si le premier caractère n'est pas dans cette liste, le module se
comporte comme si "'@'" avait été indiqué.

Note:

  The number 1023 ("0x3ff" in hexadecimal) has the following byte
  representations:

  * "03 ff" in big-endian (">")

  * "ff 03" in little-endian ("<")

  Python example:

  >>> import struct
  >>> struct.pack('>h', 1023)
  b'\x03\xff'
  >>> struct.pack('<h', 1023)
  b'\xff\x03'

Native byte order is big-endian or little-endian, depending on the
host system. For example, Intel x86, AMD64 (x86-64), and Apple M1 are
little-endian; IBM z and many legacy architectures are big-endian. Use
"sys.byteorder" to check the endianness of your system.

La taille et l'alignement natifs sont déterminés en utilisant
l'expression "sizeof" du compilateur C. Leur valeur est toujours
combinée au boutisme natif.

La taille standard dépend seulement du caractère du format ; référez-
vous au tableau dans la section Caractères de format.

Notez la différence entre "'@'" et "'='" : les deux utilisent le
boutisme natif mais la taille et l'alignement du dernier sont
standards.

The form "'!'" represents the network byte order which is always big-
endian as defined in IETF RFC 1700.

Il n'y a pas de moyen de spécifier le boutisme contraire au boutisme
natif (c'est-à-dire forcer la permutation des octets) ; utilisez le
bon caractère entre "'<'" et "'>'".

Notes :

1. Le bourrage (*padding* en anglais) n'est automatiquement ajouté
   qu'entre les membres successifs de la structure. Il n'y a pas de
   bourrage au début ou à la fin de la structure agrégée.

2. Il n'y a pas d'ajout de bourrage lorsque vous utilisez une taille
   et un alignement non-natifs, par exemple avec "'<'", "'>'", "'='"
   ou "'!'".

3. Pour aligner la fin d'une structure à l'alignement requis par un
   type particulier, terminez le format avec le code du type voulu et
   une valeur de répétition à zéro. Référez-vous à Exemples.


Caractères de format
--------------------

Les caractères de format possèdent les significations suivantes ; la
conversion entre les valeurs C et Python doit être évidente compte
tenu des types concernés. La colonne « taille standard » fait
référence à la taille en octets de la valeur agrégée avec
l'utilisation de la taille standard (c'est-à-dire lorsque la chaîne de
format commence par l'un des caractères suivants : "'<'", "'>'", "'!'"
ou "'='"). Si vous utilisez la taille native, la taille de la valeur
agrégée dépend de la plateforme.

+----------+----------------------------+----------------------+------------------+--------------+
| Format   | Type C                     | Type Python          | Taille standard  | Notes        |
|==========|============================|======================|==================|==============|
| "x"      | octet de bourrage          | pas de valeur        |                  | (7)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "c"      | char                       | *bytes* (suite       | 1                |              |
|          |                            | d'octets) de taille  |                  |              |
|          |                            | 1                    |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "b"      | signed char                | int                  | 1                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "B"      | unsigned char              | int                  | 1                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "?"      | _Bool                      | *bool* (booléen)     | 1                | (1)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "h"      | short                      | int                  | 2                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "H"      | unsigned short             | int                  | 2                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "i"      | int                        | int                  | 4                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "I"      | unsigned int               | int                  | 4                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "l"      | long                       | int                  | 4                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "L"      | unsigned long              | int                  | 4                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "q"      | long long                  | int                  | 8                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "Q"      | unsigned long long         | int                  | 8                | (2)          |
+----------+----------------------------+----------------------+------------------+--------------+
| "n"      | "ssize_t"                  | int                  |                  | (2), (3)     |
+----------+----------------------------+----------------------+------------------+--------------+
| "N"      | "size_t"                   | int                  |                  | (2), (3)     |
+----------+----------------------------+----------------------+------------------+--------------+
| "e"      | _Float16                   | *float* (nombre à    | 2                | (4), (6)     |
|          |                            | virgule flottante)   |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "f"      | float                      | *float* (nombre à    | 4                | (4)          |
|          |                            | virgule flottante)   |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "d"      | double                     | *float* (nombre à    | 8                | (4)          |
|          |                            | virgule flottante)   |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "Zf"     | float complex              | complex              | 8                | (10)         |
+----------+----------------------------+----------------------+------------------+--------------+
| "Zd"     | double complex             | complex              | 16               | (10)         |
+----------+----------------------------+----------------------+------------------+--------------+
| "s"      | char[]                     | *bytes* (séquence    |                  | (9)          |
|          |                            | d'octets)            |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "p"      | char[]                     | *bytes* (séquence    |                  | (8)          |
|          |                            | d'octets)            |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "P"      | void*                      | int                  |                  | (2), (5)     |
+----------+----------------------------+----------------------+------------------+--------------+

Modifié dans la version 3.3: ajouté la gestion des formats "'n'" et
"'N'".

Modifié dans la version 3.6: ajouté la gestion du format "'e'".

Modifié dans la version 3.14: Added support for the "'F'" and "'D'"
formats.

Modifié dans la version 3.15: Added support for the "'Zf'" and "'Zd'"
formats. "'F'" and "'D'" formats are *soft deprecated*.

Voir aussi:

  The "array" and ctypes modules, as well as third-party modules like
  numpy, use similar -- but slightly different -- type codes.

Notes :

1. The "'?'" conversion code corresponds to the _Bool type defined by
   C standards since C99.  In standard mode, it is represented by one
   byte.

2. When attempting to pack a non-integer using any of the integer
   conversion codes, if the non-integer has a "__index__()" method
   then that method is called to convert the argument to an integer
   before packing.

   Modifié dans la version 3.2: Added use of the "__index__()" method
   for non-integers.

3. Les codes de conversion "'n'" et "'N'" ne sont disponibles que pour
   la taille native (choisie par défaut ou à l'aide du caractère de
   boutisme "'@'"). Pour la taille standard, vous pouvez utiliser
   n'importe quel format d'entier qui convient à votre application.

4. Pour les codes de conversion "'f'", "'d'" et "'e'", la
   représentation agrégée utilise respectivement le format IEEE 754
   *binaire32*, *binaire64* ou *binaire16* (pour "'f'", "'d'" ou "'e'"
   respectivement), quel que soit le format des nombres à virgule
   flottante de la plateforme.

5. Le caractère de format "'P'" n'est disponible que pour le boutisme
   natif (choisi par défaut ou à l'aide du caractère "'@'" de
   boutisme). Le caractère de boutisme "'='" choisit d'utiliser un
   petit ou un gros en fonction du système hôte. Le module *struct* ne
   l'interprète pas comme un boutisme natif, donc le format "'P'"
   n'est pas disponible.

6. The IEEE 754 binary16 "half precision" type was introduced in the
   2008 revision of the IEEE 754 standard. It has a sign bit, a 5-bit
   exponent and 11-bit precision (with 10 bits explicitly stored), and
   can represent numbers between approximately "6.1e-05" and "6.5e+04"
   at full precision. This type is not widely supported by C
   compilers: it's available as _Float16 type, if the compiler
   supports the Annex H of the C23 standard.  On a typical machine, an
   unsigned short can be used for storage, but not for math
   operations. See the Wikipedia page on the half-precision floating-
   point format for more information.

7. When packing, "'x'" inserts one NUL byte.

8. The "'p'" format character encodes a "Pascal string", meaning a
   short variable-length string stored in a *fixed number of bytes*,
   given by the count. The first byte stored is the length of the
   string, or 255, whichever is smaller.  The bytes of the string
   follow.  If the byte string passed in to "pack()" is too long
   (longer than the count minus 1), only the leading "count-1" bytes
   of the string are stored.  If the byte string is shorter than
   "count-1", it is padded with null bytes so that exactly count bytes
   in all are used.  Note that for "unpack()", the "'p'" format
   character consumes "count" bytes, but that the "bytes" object
   returned can never contain more than 255 bytes. When packing,
   arguments of types "bytes" and "bytearray" are accepted.

9. For the "'s'" format character, the count is interpreted as the
   length of the byte string, not a repeat count like for the other
   format characters; for example, "'10s'" means a single 10-byte
   string mapping to or from a single Python byte string, while
   "'10c'" means 10 separate one byte character elements (e.g.,
   "cccccccccc") mapping to or from ten different Python byte objects.
   (See Exemples for a concrete demonstration of the difference.) If a
   count is not given, it defaults to 1.  For packing, the byte string
   is truncated or padded with null bytes as appropriate to make it
   fit. For unpacking, the resulting "bytes" object always has exactly
   the specified number of bytes.  As a special case, "'0s'" means a
   single, empty byte string (while "'0c'" means 0 characters). When
   packing, arguments of types "bytes" and "bytearray" are accepted.

10. For the "'Zf'" and "'Zd'" type codes, the packed representation
    uses the IEEE 754 binary32 and binary64 format for components of
    the complex number, regardless of the floating-point format used
    by the platform. Note that complex types are available
    unconditionally, despite complex types being an optional feature
    in C. As specified in the C11 standard, each complex type is
    represented by a two-element C array containing, respectively, the
    real and imaginary parts. The "'F'" and "'D'" (for "'Zf'" and
    "'Zd'", respectively) format characters are supported for
    compatibility.

Un caractère de format peut être précédé par un entier indiquant le
nombre de répétitions. Par exemple, la chaîne de format "'4h'" a
exactement la même signification que "'hhhh'".

Les caractères d'espacement entre les indications de format sont
ignorés ; cependant, le nombre de répétitions et le format associé ne
doivent pas être séparés par des caractères d'espacement.

Lors de l'agrégation d'une valeur "x" en utilisant l'un des formats
pour les entiers ("'b'", "'B'", "'h'", "'H'", "'i'", "'I'", "'l'",
"'L'", "'q'", "'Q'"), si "x" est en dehors de l'intervalle du format
spécifié, une "struct.error" est levée.

Modifié dans la version 3.1: Previously, some of the integer formats
wrapped out-of-range values and raised "DeprecationWarning" instead of
"struct.error".

Pour le caractère de format "'?'", la valeur renvoyée est "True" ou
"False". Lors de l'agrégation, la valeur de vérité de l'objet argument
est utilisée. La valeur agrégée est 0 ou 1 dans la représentation
native ou standard et, lors de la dissociation, n'importe quelle
valeur différente de zéro est renvoyée "True".


Exemples
--------

Note:

  Native byte order examples (designated by the "'@'" format prefix or
  lack of any prefix character) may not match what the reader's
  machine produces as that depends on the platform and compiler.

Pack and unpack integers of three different sizes, using big endian
ordering:

   >>> from struct import *
   >>> pack(">bhl", 1, 2, 3)
   b'\x01\x00\x02\x00\x00\x00\x03'
   >>> unpack('>bhl', b'\x01\x00\x02\x00\x00\x00\x03')
   (1, 2, 3)
   >>> calcsize('>bhl')
   7

Attempt to pack an integer which is too large for the defined field:

   >>> pack(">h", 99999)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   struct.error: 'h' format requires -32768 <= number <= 32767

Demonstrate the difference between "'s'" and "'c'" format characters:

   >>> pack("@ccc", b'1', b'2', b'3')
   b'123'
   >>> pack("@3s", b'123')
   b'123'

Les champs dissociés peuvent être nommés en leur assignant des
variables ou en encapsulant le résultat dans un *n*-uplet nommé :

   >>> record = b'raymond   \x32\x12\x08\x01\x08'
   >>> name, serialnum, school, gradelevel = unpack('<10sHHb', record)

   >>> from collections import namedtuple
   >>> Student = namedtuple('Student', 'name serialnum school gradelevel')
   >>> Student._make(unpack('<10sHHb', record))
   Student(name=b'raymond   ', serialnum=4658, school=264, gradelevel=8)

The ordering of format characters may have an impact on size in native
mode since padding is implicit. In standard mode, the user is
responsible for inserting any desired padding. Note in the first
"pack" call below that three NUL bytes were added after the packed
"'#'" to align the following integer on a four-byte boundary. In this
example, the output was produced on a little endian machine:

   >>> pack('@ci', b'#', 0x12131415)
   b'#\x00\x00\x00\x15\x14\x13\x12'
   >>> pack('@ic', 0x12131415, b'#')
   b'\x15\x14\x13\x12#'
   >>> calcsize('@ci')
   8
   >>> calcsize('@ic')
   5

The following format "'llh0l'" results in two pad bytes being added at
the end, assuming the platform's longs are aligned on 4-byte
boundaries:

   >>> pack('@llh0l', 1, 2, 3)
   b'\x00\x00\x00\x01\x00\x00\x00\x02\x00\x03\x00\x00'

Voir aussi:

  Module "array"
     Stockage agrégé binaire de données homogènes.

  Module "json"
     JSON encoder and decoder.

  Module "pickle"
     Python object serialization.


Applications
============

Two main applications for the "struct" module exist, data interchange
between Python and C code within an application or another application
compiled using the same compiler (native formats), and data
interchange between applications using agreed upon data layout
(standard formats).  Generally speaking, the format strings
constructed for these two domains are distinct.


Native Formats
--------------

When constructing format strings which mimic native layouts, the
compiler and machine architecture determine byte ordering and padding.
In such cases, the "@" format character should be used to specify
native byte ordering and data sizes.  Internal pad bytes are normally
inserted automatically.  It is possible that a zero-repeat format code
will be needed at the end of a format string to round up to the
correct byte boundary for proper alignment of consecutive chunks of
data.

Consider these two simple examples (on a 64-bit, little-endian
machine):

   >>> calcsize('@lhl')
   24
   >>> calcsize('@llh')
   18

Data is not padded to an 8-byte boundary at the end of the second
format string without the use of extra padding.  A zero-repeat format
code solves that problem:

   >>> calcsize('@llh0l')
   24

The "'x'" format code can be used to specify the repeat, but for
native formats it is better to use a zero-repeat format like "'0l'".

By default, native byte ordering and alignment is used, but it is
better to be explicit and use the "'@'" prefix character.


Standard Formats
----------------

When exchanging data beyond your process such as networking or
storage, be precise.  Specify the exact byte order, size, and
alignment.  Do not assume they match the native order of a particular
machine. For example, network byte order is big-endian, while many
popular CPUs are little-endian.  By defining this explicitly, the user
need not care about the specifics of the platform their code is
running on. The first character should typically be "<" or ">" (or
"!").  Padding is the responsibility of the programmer.  The zero-
repeat format character won't work.  Instead, the user must explicitly
add "'x'" pad bytes where needed.  Revisiting the examples from the
previous section, we have:

   >>> calcsize('<qh6xq')
   24
   >>> pack('<qh6xq', 1, 2, 3) == pack('@lhl', 1, 2, 3)
   True
   >>> calcsize('@llh')
   18
   >>> pack('@llh', 1, 2, 3) == pack('<qqh', 1, 2, 3)
   True
   >>> calcsize('<qqh6x')
   24
   >>> calcsize('@llh0l')
   24
   >>> pack('@llh0l', 1, 2, 3) == pack('<qqh6x', 1, 2, 3)
   True

The above results (executed on a 64-bit machine) aren't guaranteed to
match when executed on different machines.  For example, the examples
below were executed on a 32-bit machine:

   >>> calcsize('<qqh6x')
   24
   >>> calcsize('@llh0l')
   12
   >>> pack('@llh0l', 1, 2, 3) == pack('<qqh6x', 1, 2, 3)
   False


Classes
=======

The "struct" module also defines the following type:

class struct.Struct(format)

   Return a new Struct object which writes and reads binary data
   according to the format string *format*.  Creating a "Struct"
   object once and calling its methods is more efficient than calling
   module-level functions with the same format since the format string
   is only compiled once.

   Note:

     The compiled versions of the most recent format strings passed to
     the module-level functions are cached, so programs that use only
     a few format strings needn't worry about reusing a single
     "Struct" instance.

   Les objets "Struct" compilés gèrent les méthodes et attributs
   suivants :

   pack(v1, v2, ...)

      Identique à la fonction "pack()", en utilisant le format compilé
      ("len(result)" vaut "size").

   pack_into(buffer, offset, v1, v2, ...)

      Identique à la fonction "pack_into()", en utilisant le format
      compilé.

   unpack(buffer)

      Identique à la fonction "unpack()", en utilisant le format
      compilé. La taille du tampon *buffer* en octets doit valoir
      "size".

   unpack_from(buffer, offset=0)

      Identique à la fonction "unpack_from()", en utilisant le format
      compilé. La taille du tampon *buffer* en octets, en commençant à
      la position *offset*, doit valoir au moins "size".

   iter_unpack(buffer)

      Identique à la fonction "iter_unpack()", en utilisant le format
      compilé. La taille du tampon *buffer* en octets doit être un
      multiple de "size".

      Ajouté dans la version 3.4.

   format

      La chaîne de format utilisée pour construire l'objet "Struct".

      Modifié dans la version 3.7: la chaîne de format est maintenant
      de type "str" au lieu de "bytes".

   size

      La taille calculée de la structure agrégée (et donc de l'objet
      "bytes" produit par la méthode "pack()") correspondante à
      "format".

   Modifié dans la version 3.13: The *repr()* of structs has changed.
   It is now:

   >>> Struct('i')
   Struct('i')
