"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, ...)

   Agrège les valeurs *v1*, *v2*… conformément à la chaîne de format
   *format* et écrit les octets agrégés dans le tampon *buffer*, en
   commençant à la position *offset*. Notez que *offset* est un
   argument obligatoire.

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)

   Dissocie les éléments du tampon *buffer*, en commençant à la
   position *offset*, conformément à la chaîne de format *format*. Le
   résultat est un n-uplet, qui peut éventuellement ne contenir qu'un
   seul élément. La taille du tampon en octets, en commençant à la
   position *offset*, doit être au moins égale à la taille requise par
   le format, telle que calculée par "calcsize()".

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 type codes, 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.

Standard size depends only on the type code;  see the table in the
Type Codes section.

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.


Type Codes
----------

Type codes (or format codes) have the following meaning; the
conversion between C and Python values should be obvious given their
types.  The 'Standard size' column refers to the size of the packed
value in bytes when using standard size; that is, when the format
string starts with one of "'<'", "'>'", "'!'" or "'='".  When using
native size, the size of the packed value is platform-dependent.

+----------+----------------------------+----------------------+------------------+--------------+
| 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)   |                  |              |
+----------+----------------------------+----------------------+------------------+--------------+
| "F"      | float complex              | complex              | 8                | (10)         |
+----------+----------------------------+----------------------+------------------+--------------+
| "D"      | double complex             | complex              | 16               | (10)         |
+----------+----------------------------+----------------------+------------------+--------------+
| "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.

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. The "'P'" type code is only available for the native byte ordering
   (selected as the default or with the "'@'" byte order character).
   The byte order character "'='" chooses to use little- or big-endian
   ordering based on the host system. The struct module does not
   interpret this as native ordering, so the "'P'" format is not
   available.

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'" type code 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'" type code 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'" type code, the count is interpreted as the length of
   the byte string, not a repeat count like for the other type codes;
   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 "'F'" and "'D'" 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 ("F"/"Zf" and "D"/"Zd") 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.

A type code may be preceded by an integral repeat count.  For example,
the format string "'4h'" means exactly the same as "'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".

For the "'?'" type code, the return value is either "True" or "False".
When packing, the truth value of the argument object is used. Either 0
or 1 in the native or standard bool representation will be packed, and
any non-zero value will be "True" when unpacking.


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 type codes 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 type 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'" type 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')
