"base64" --- Base16, Base32, Base64, Base85 Data Encodings
**********************************************************

**Code source :** Lib/base64.py

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

This module provides functions for encoding binary data to printable
ASCII characters and decoding such encodings back to binary data. This
includes the encodings specified in **RFC 4648** (Base64, Base32 and
Base16), the Base85 encoding specified in PDF 2.0, and non-standard
variants of Base85 used elsewhere.

There are two interfaces provided by this module.  The modern
interface supports encoding *bytes-like objects* to ASCII "bytes", and
decoding *bytes-like objects* or strings containing ASCII to "bytes".
Both base-64 alphabets defined in **RFC 4648** (normal, and URL- and
filesystem-safe) are supported.

The legacy interface does not support decoding from strings, but it
does provide functions for encoding and decoding to and from *file
objects*.  It only supports the Base64 standard alphabet, and it adds
newlines every 76 characters as per **RFC 2045**.  Note that if you
are looking for **RFC 2045** support you probably want to be looking
at the "email" package instead.

Modifié dans la version 3.3: Les chaînes de caractères Unicode
contenant uniquement des caractères ASCII sont désormais acceptées par
les fonctions de décodage de l'interface moderne.

Modifié dans la version 3.4: Tous les *objets octet-compatibles* sont
désormais acceptés par l'ensemble des fonctions d'encodage et de
décodage de ce module. La gestion de Ascii85/base85 a été ajoutée.


RFC 4648 Encodings
==================

The **RFC 4648** encodings are suitable for encoding binary data so
that it can be safely sent by email, used as parts of URLs, or
included as part of an HTTP POST request.

base64.b64encode(s, altchars=None, *, padded=True, wrapcol=0)

   Encode un *objet octet-compatible* *s* en utilisant l'algorithme
   base64 et renvoie les "bytes" encodés.

   Optional *altchars* must be a *bytes-like object* of length 2 which
   specifies an alternative alphabet for the "+" and "/" characters.
   This allows an application to e.g. generate URL or filesystem safe
   Base64 strings.  The default is "None", for which the standard
   Base64 alphabet is used.

   If *padded* is true (default), pad the encoded data with the '='
   character to a size multiple of 4. If *padded* is false, do not add
   the pad characters.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   Modifié dans la version 3.15: Added the *padded* and *wrapcol*
   parameters.

base64.b64decode(s, altchars=None, validate=False, *, padded=True, canonical=False)
base64.b64decode(s, altchars=None, validate=True, *, ignorechars, padded=True, canonical=False)

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* encodée en base64 et renvoie les "bytes" décodés.

   Optional *altchars* must be a *bytes-like object* or ASCII string
   of length 2 which specifies the alternative alphabet used instead
   of the "+" and "/" characters.

   If *padded* is true, the last group of 4 base 64 alphabet
   characters must be padded with the '=' character. If *padded* is
   false, padding is neither required nor recognized: the '='
   character is not treated as padding but as a non-alphabet
   character, which means it is silently discarded when *validate* is
   false, or causes an "Error" when *validate* is true unless b'=' is
   included in *ignorechars*.

   Une exception "binascii.Error" est levée si *s* n'est pas remplie à
   une longueur attendue.

   If *ignorechars* is specified, it should be a *bytes-like object*
   containing characters to ignore from the input when *validate* is
   true. If *ignorechars* contains the pad character "'='",  the pad
   characters presented before the end of the encoded data and the
   excess pad characters will be ignored. The default value of
   *validate* is "True" if *ignorechars* is specified, "False"
   otherwise.

   If *validate* is false, characters that are neither in the normal
   base-64 alphabet nor (if *ignorechars* is not specified) the
   alternative alphabet are discarded prior to the padding check, but
   the "+" and "/" characters keep their meaning if they are not in
   *altchars* (they will be discarded in future Python versions).

   If *validate* is true, these non-alphabet characters in the input
   result in a "binascii.Error".

   If *canonical* is true, non-zero padding bits are rejected. See
   "binascii.a2b_base64()" for details.

   For more information about the strict base64 check, see
   "binascii.a2b_base64()"

   Modifié dans la version 3.15: Added the *canonical*, *ignorechars*,
   and *padded* parameters.

   Obsolète depuis la version 3.15: Accepting the "+" and "/"
   characters with an alternative alphabet is now deprecated.

base64.standard_b64encode(s)

   Encode un *objet octet-compatible* *s* en utilisant l'alphabet
   standard base64 et renvoie les "bytes" encodés.

base64.standard_b64decode(s)

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* utilisant l'alphabet base64 standard et renvoie les
   "bytes" décodés.

base64.urlsafe_b64encode(s, *, padded=True)

   Encode *bytes-like object* *s* using the URL- and filesystem-safe
   alphabet, which substitutes "-" instead of "+" and "_" instead of
   "/" in the standard Base64 alphabet, and return the encoded
   "bytes".  The result can still contain "=" if *padded* is true
   (default).

   Modifié dans la version 3.15: Added the *padded* parameter.

base64.urlsafe_b64decode(s, *, padded=False)

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* utilisant un alphabet sûr pour les URL et systèmes de
   fichiers qui substitue "-" et "_" à "+" et "/" dans l'alphabet
   standard base64 et renvoie les "bytes" décodés.

   Modifié dans la version 3.15: Added the *padded* parameter. Padding
   of input is no longer required by default.

   Obsolète depuis la version 3.15: Accepting the "+" and "/"
   characters is now deprecated.

base64.b32encode(s, *, padded=True, wrapcol=0)

   Encode un *objet byte-compatible* *s* en utilisant l'algorithme
   base32 et renvoie les "bytes" encodés.

   If *padded* is true (default), pad the encoded data with the '='
   character to a size multiple of 8. If *padded* is false, do not add
   the pad characters.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not add any newlines.

   Modifié dans la version 3.15: Added the *padded* and *wrapcol*
   parameters.

base64.b32decode(s, casefold=False, map01=None, *, padded=True, ignorechars=b'', canonical=False)

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* encodé en base32 et renvoie les "bytes" décodés.

   L'option *casefold* est un drapeau spécifiant si l'utilisation d'un
   alphabet en minuscules est acceptable comme entrée. Pour des
   raisons de sécurité, cette option est à "False" par défaut.

   **RFC 4648** allows for optional mapping of the digit 0 (zero) to
   the letter O (oh), and for optional mapping of the digit 1 (one) to
   either the letter I (eye) or letter L (el).  The optional argument
   *map01* when not "None", specifies which letter the digit 1 should
   be mapped to (when *map01* is not "None", the digit 0 is always
   mapped to the letter O).  For security purposes the default is
   "None", so that 0 and 1 are not allowed in the input.

   If *padded* is true, the last group of 8 base 32 alphabet
   characters must be padded with the '=' character. If *padded* is
   false, padding is neither required nor recognized: the '='
   character is not treated as padding but as a non-alphabet
   character, which means it raises an "Error" unless b'=' is included
   in *ignorechars*.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   If *canonical* is true, non-zero padding bits are rejected. See
   "binascii.a2b_base32()" for details.

   Une exception "binascii.Error" est levée si *s* n'est pas remplie à
   une longueur attendue ou si elle contient des caractères hors de
   l'alphabet.

   Modifié dans la version 3.15: Added the *canonical*, *ignorechars*,
   and *padded* parameters.

base64.b32hexencode(s, *, padded=True, wrapcol=0)

   Similar to "b32encode()" but uses the Extended Hex Alphabet, as
   defined in **RFC 4648**.

   Ajouté dans la version 3.10.

   Modifié dans la version 3.15: Added the *padded* and *wrapcol*
   parameters.

base64.b32hexdecode(s, casefold=False, *, padded=True, ignorechars=b'', canonical=False)

   Similar to "b32decode()" but uses the Extended Hex Alphabet, as
   defined in **RFC 4648**.

   This version does not allow the digit 0 (zero) to the letter O (oh)
   and digit 1 (one) to either the letter I (eye) or letter L (el)
   mappings, all these characters are included in the Extended Hex
   Alphabet and are not interchangeable.

   Ajouté dans la version 3.10.

   Modifié dans la version 3.15: Added the *canonical*, *ignorechars*,
   and *padded* parameters.

base64.b16encode(s, *, wrapcol=0)

   Encode un *objet byte-compatible* *s* en utilisant l'algorithme
   base16 et renvoie les "bytes" encodés.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not add any newlines.

   Modifié dans la version 3.15: Added the *wrapcol* parameter.

base64.b16decode(s, casefold=False, *, ignorechars=b'')

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* encodé en base16 et renvoie les "bytes" décodés.

   L'option *casefold* est un drapeau spécifiant si l'utilisation d'un
   alphabet en minuscules est acceptable comme entrée. Pour des
   raisons de sécurité, cette option est à "False" par défaut.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   Une exception "binascii.Error" est levée si *s* n'est pas remplie à
   une longueur attendue ou si elle contient des caractères hors de
   l'alphabet.

   Modifié dans la version 3.15: Added the *ignorechars* parameter.


Base85 Encodings
================

Base85 encoding is a family of algorithms which represent four bytes
using five ASCII characters.  Originally implemented in the Unix
"btoa(1)" utility, a version of it was later adopted by Adobe in the
PostScript language and is standardized in PDF 2.0 (ISO 32000-2). This
version, in both its "btoa" and PDF variants, is implemented by
"a85encode()".

A separate version, using a different output character set, was
defined as an April Fool's joke in **RFC 1924** but is now used by Git
and other software.  This version is implemented by "b85encode()".

Finally, a third version, using yet another output character set
designed for safe inclusion in programming language strings, is
defined by ZeroMQ and implemented here by "z85encode()".

The functions present in this module differ in how they handle the
following:

* Whether to include and expect enclosing "<~" and "~>" markers.

* Whether to fold the input into multiple lines.

* The set of ASCII characters used for encoding.

* Compact encodings of sequences of spaces and null bytes.

* The encoding of zero-padding bytes applied to the input.

Refer to the documentation of the individual functions for more
information.

base64.a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False)

   Encode un *objet byte-compatible* *s* en utilisant l'algorithme
   Ascii85 et renvoie les "bytes" encodés.

   *foldspaces* is an optional flag that uses the special short
   sequence 'y' instead of 4 consecutive spaces (ASCII 0x20) as
   supported by 'btoa'. This feature is not supported by the standard
   encoding used in PDF.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not insert any newlines.

   *pad* controls whether zero-padding applied to the end of the input
   is fully retained in the output encoding, as done by "btoa",
   producing an exact multiple of 5 bytes of output. This is not part
   of the standard encoding used in PDF, as it does not preserve the
   length of the data.

   *adobe* controls whether the encoded byte sequence is framed with
   "<~" and "~>", as in a PostScript base-85 string literal.  Note
   that while ASCII85Decode streams in PDF documents *must* be
   terminated with "~>", they *must not* use a leading "<~".

   Ajouté dans la version 3.4.

base64.a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \t\n\r\x0b', canonical=False)

   Décode un *objet octet-compatible* ou une chaîne de caractères
   ASCII *s* encodé en Ascii85 et renvoie les "bytes" décodés.

   *foldspaces* is a flag that specifies whether the 'y' short
   sequence should be accepted as shorthand for 4 consecutive spaces
   (ASCII 0x20). This feature is not supported by the standard Ascii85
   encoding used in PDF and PostScript.

   *adobe* controls whether the "<~" and "~>" markers are present.
   While the leading "<~" is not required, the input must end with
   "~>", or a "ValueError" is raised.

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input. This should only contain whitespace
   characters, and by default contains all whitespace characters in
   ASCII.

   If *canonical* is true, non-canonical encodings are rejected. See
   "binascii.a2b_ascii85()" for details.

   Ajouté dans la version 3.4.

   Modifié dans la version 3.15: Added the *canonical* parameter.
   Single-character final groups are now always rejected as encoding
   violations.

base64.b85encode(b, pad=False, *, wrapcol=0)

   Encode un *objet byte-compatible* *s* en utilisant l'algorithme
   base85 (tel qu'utilisé par exemple par le programme *git-diff* sur
   des données binaires) et renvoie les "bytes" encodés.

   The input is padded with "b'\0'" so its length is a multiple of 4
   bytes before encoding.  If *pad* is true, all the resulting
   characters are retained in the output, which will always be a
   multiple of 5 bytes, and thus the length of the data may not be
   preserved on decoding.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not add any newlines.

   Ajouté dans la version 3.4.

   Modifié dans la version 3.15: Added the *wrapcol* parameter.

base64.b85decode(b, *, ignorechars=b'', canonical=False)

   Decode the base85-encoded *bytes-like object* or ASCII string *b*
   and return the decoded "bytes".

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   If *canonical* is true, non-canonical encodings are rejected. See
   "binascii.a2b_base85()" for details.

   Ajouté dans la version 3.4.

   Modifié dans la version 3.15: Added the *canonical* and
   *ignorechars* parameters. Single-character final groups are now
   always rejected as encoding violations.

base64.z85encode(s, pad=False, *, wrapcol=0)

   Encode the *bytes-like object* *s* using Z85 (as used in ZeroMQ)
   and return the encoded "bytes".

   The input is padded with "b'\0'" so its length is a multiple of 4
   bytes before encoding.  If *pad* is true, all the resulting
   characters are retained in the output, which will always be a
   multiple of 5 bytes, as required by the ZeroMQ standard.

   If *wrapcol* is non-zero, insert a newline ("b'\n'") character
   after at most every *wrapcol* characters. If *wrapcol* is zero
   (default), do not add any newlines.

   Ajouté dans la version 3.13.

   Modifié dans la version 3.15: The *pad* parameter was added.

   Modifié dans la version 3.15: Added the *wrapcol* parameter.

base64.z85decode(s, *, ignorechars=b'', canonical=False)

   Decode the Z85-encoded *bytes-like object* or ASCII string *s* and
   return the decoded "bytes".

   *ignorechars* should be a *bytes-like object* containing characters
   to ignore from the input.

   If *canonical* is true, non-canonical encodings are rejected. See
   "binascii.a2b_base85()" for details.

   Ajouté dans la version 3.13.

   Modifié dans la version 3.15: Added the *canonical* and
   *ignorechars* parameters. Single-character final groups are now
   always rejected as encoding violations.


Legacy Interface
================

base64.decode(input, output)

   Décode le contenu d'un fichier binaire *input* et écrit les données
   binaires résultantes dans le fichier *output*. *input* et *output*
   doivent être des *objets fichiers*. *input* est lu jusqu'à ce que
   "input.readline()" renvoie un objet *bytes* vide.

base64.decodebytes(s)

   Décode un *objet octet-compatible* *s* devant contenir une ou
   plusieurs lignes de données encodées en base64 et renvoie les
   "bytes" décodés.

   Ajouté dans la version 3.1.

base64.encode(input, output)

   Encode le contenu du fichier binaire *input* et écrit les données
   encodées en base64 résultantes dans le fichier *output. *input* et
   *output* doivent être des *objets fichiers*. *input* est lu jusqu'à
   ce que "input.readline()" renvoie un objet *bytes* vide. "encode()"
   insère un caractère de saut de ligne ("b'\n'") tous les 76 octets
   de sortie et assure que celle-ci se termine par une nouvelle ligne,
   comme spécifié par la **RFC 2045** (MIME).

base64.encodebytes(s)

   Encode un *objet octet-compatible* *s* pouvant contenir des données
   binaires arbitraires et renvoie les "bytes" contenant les données
   encodées en base64. Un caractère de saut de ligne ("b'\n'") est
   inséré tous les 76 octets de sortie et celle-ci se termine par une
   nouvelle ligne, comme spécifié par la **RFC 2045** (MIME).

   Ajouté dans la version 3.1.

Un exemple d'utilisation du module :

>>> import base64
>>> encoded = base64.b64encode(b'data to be encoded')
>>> encoded
b'ZGF0YSB0byBiZSBlbmNvZGVk'
>>> data = base64.b64decode(encoded)
>>> data
b'data to be encoded'


Considérations de sécurité
==========================

A new security considerations section was added to **RFC 4648**
(section 12); it's recommended to review the security section for any
code deployed to production.

Voir aussi:

  Module "binascii"
     Module secondaire contenant les conversions ASCII vers binaire et
     binaire vers ASCII.

  **RFC 1521** — MIME (*Multipurpose Internet Mail Extensions*) *Part
  One: Mechanisms for Specifying and Describing the Format of Internet
  Message Bodies*
     La Section 5.2, "*Base64 Content-Transfer-Encoding*", donne la
     définition de l'encodage base64.

  ISO 32000-2 Portable document format - Part 2: PDF 2.0
     Section 7.4.3, "ASCII85Decode Filter," provides the definition of
     the Ascii85 encoding used in PDF and PostScript, including the
     output character set and the details of data length preservation
     using zero-padding and partial output groups.

  ZeroMQ RFC 32/Z85
     The "Formal Specification" section provides the character set
     used in Z85.
