# `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.