base64 — Base16, Base32, Base64, Base85 Data Encodings数据编码

Source code: Lib/base64.py

This module provides functions for encoding binary data to printable ASCII characters and decoding such encodings back to binary data. 该模块提供将二进制数据编码为可打印ASCII字符并将此类编码解码回二进制数据的功能。It provides encoding and decoding functions for the encodings specified in RFC 4648, which defines the Base16, Base32, and Base64 algorithms, and for the de-facto standard Ascii85 and Base85 encodings.它为RFC 4648（定义了Base16、Base32和Base64算法）中指定的编码以及事实上的标准Ascii85和Base85编码提供了编码和解码功能。

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. RFC 4648编码适用于对二进制数据进行编码，以便可以通过电子邮件安全发送、用作URL的一部分或作为HTTP POST请求的一部分。The encoding algorithm is not the same as the uuencode program.编码算法与uuencode程序不同。

There are two interfaces provided by this module. 该模块提供两个接口。The modern interface supports encoding bytes-like objects to ASCII bytes, and decoding bytes-like objects or strings containing ASCII to bytes. 现代接口支持将类字节对象编码为ASCIIbytes，并将类字节对象或包含ASCII的字符串解码为bytes。Both base-64 alphabets defined in RFC 4648 (normal, and URL- and filesystem-safe) are supported.支持RFC 4648中定义的base-64字母表（正常，URL和文件系统安全）。

The legacy interface does not support decoding from strings, but it does provide functions for encoding and decoding to and from file objects. 传统接口不支持从字符串解码，但它提供了对文件对象进行编码和解码的功能。It only supports the Base64 standard alphabet, and it adds newlines every 76 characters as per RFC 2045. 它只支持Base64标准字母表，并根据RFC 2045每76个字符添加一行换行符。Note that if you are looking for RFC 2045 support you probably want to be looking at the email package instead.注意，如果您正在寻找RFC 2045支持，您可能希望查看email包。

Changed in version 3.3:版本3.3中更改： ASCII-only Unicode strings are now accepted by the decoding functions of the modern interface.现代接口的解码功能现在只接受ASCII Unicode字符串。

Changed in version 3.4:版本3.4中更改： Any bytes-like objects are now accepted by all encoding and decoding functions in this module. 此模块中的所有编码和解码函数现在都接受任何类字节的对象。Ascii85/Base85 support added.增加了Ascii85/Base85支持。

The modern interface provides:现代界面提供：

base64.b64encode(s, altchars=None)

Encode the bytes-like object s using Base64 and return the encoded bytes.使用Base64对类字节对象s进行编码，并返回编码的bytes。

Optional altchars must be a bytes-like object of at least length 2 (additional characters are ignored) 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.

base64.b64decode(s, altchars=None, validate=False)

Decode the Base64 encoded bytes-like object or ASCII string s and return the decoded bytes.

Optional altchars must be a bytes-like object or ASCII string of at least length 2 (additional characters are ignored) which specifies the alternative alphabet used instead of the + and / characters.

A binascii.Error exception is raised if s is incorrectly padded.

If validate is False (the default), characters that are neither in the normal base-64 alphabet nor the alternative alphabet are discarded prior to the padding check. If validate is True, these non-alphabet characters in the input result in a binascii.Error.

base64.standard_b64encode(s)

Encode bytes-like object s using the standard Base64 alphabet and return the encoded bytes.

base64.standard_b64decode(s)

Decode bytes-like object or ASCII string s using the standard Base64 alphabet and return the decoded bytes.

base64.urlsafe_b64encode(s)

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 =.

base64.urlsafe_b64decode(s)

Decode bytes-like object or ASCII string s using the URL- and filesystem-safe alphabet, which substitutes - instead of + and _ instead of / in the standard Base64 alphabet, and return the decoded bytes.

base64.b32encode(s)

Encode the bytes-like object s using Base32 and return the encoded bytes.

base64.b32decode(s, casefold=False, map01=None)

Decode the Base32 encoded bytes-like object or ASCII string s and return the decoded bytes.

Optional casefold is a flag specifying whether a lowercase alphabet is acceptable as input. For security purposes, the default is False.

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.

A binascii.Error is raised if s is incorrectly padded or if there are non-alphabet characters present in the input.

base64.b32hexencode(s)

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

New in version 3.10.版本3.10中新增。

base64.b32hexdecode(s, casefold=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.

New in version 3.10.版本3.10中新增。

base64.b16encode(s)

Encode the bytes-like object s using Base16 and return the encoded bytes.

base64.b16decode(s, casefold=False)

Decode the Base16 encoded bytes-like object or ASCII string s and return the decoded bytes.

Optional casefold is a flag specifying whether a lowercase alphabet is acceptable as input. For security purposes, the default is False.

A binascii.Error is raised if s is incorrectly padded or if there are non-alphabet characters present in the input.

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

Encode the bytes-like object b using Ascii85 and return the encoded bytes.

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” Ascii85 encoding.

wrapcol controls whether the output should have newline (b'\n') characters added to it. If this is non-zero, each output line will be at most this many characters long.

pad controls whether the input is padded to a multiple of 4 before encoding. Note that the btoa implementation always pads.

adobe controls whether the encoded byte sequence is framed with <~ and ~>, which is used by the Adobe implementation.

New in version 3.4.版本3.4中新增。

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

Decode the Ascii85 encoded bytes-like object or ASCII string b and return the decoded bytes.

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.

adobe controls whether the input sequence is in Adobe Ascii85 format (i.e. is framed with <~ and ~>).

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

New in version 3.4.版本3.4中新增。

base64.b85encode(b, pad=False)

Encode the bytes-like object b using base85 (as used in e.g. git-style binary diffs) and return the encoded bytes.

If pad is true, the input is padded with b'\0' so its length is a multiple of 4 bytes before encoding.

New in version 3.4.版本3.4中新增。

base64.b85decode(b)

Decode the base85-encoded bytes-like object or ASCII string b and return the decoded bytes. Padding is implicitly removed, if necessary.

New in version 3.4.版本3.4中新增。

The legacy interface:

base64.decode(input, output)

Decode the contents of the binary input file and write the resulting binary data to the output file. input and output must be file objects. input will be read until input.readline() returns an empty bytes object.

base64.decodebytes(s)

Decode the bytes-like object s, which must contain one or more lines of base64 encoded data, and return the decoded bytes.

New in version 3.1.版本3.1中新增。

base64.encode(input, output)

Encode the contents of the binary input file and write the resulting base64 encoded data to the output file. input and output must be file objects. input will be read until input.read() returns an empty bytes object. encode() inserts a newline character (b'\n') after every 76 bytes of the output, as well as ensuring that the output always ends with a newline, as per RFC 2045 (MIME).

base64.encodebytes(s)

Encode the bytes-like object s, which can contain arbitrary binary data, and return bytes containing the base64-encoded data, with newlines (b'\n') inserted after every 76 bytes of output, and ensuring that there is a trailing newline, as per RFC 2045 (MIME).

New in version 3.1.版本3.1中新增。

An example usage of the module:模块的用法示例：

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

Security Considerations安全注意事项

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.RFC 4648增加了新的安全考虑部分（第12节）；对于部署到生产环境的任何代码，建议查看安全部分。

See also另请参见

Module binascii

Support module containing ASCII-to-binary and binary-to-ASCII conversions.支持包含ASCII到二进制和二进制到ASCII转换的模块。

RFC 1521 - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message BodiesMIME（多用途Internet邮件扩展）第一部分：指定和描述Internet消息体格式的机制

Section 5.2, “Base64 Content-Transfer-Encoding,” provides the definition of the base64 encoding.第5.2节，“Base64内容传输编码”提供了Base64编码的定义。