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codecs — 编解码器注册和基类

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`codecs` — 编解码器注册和基类 ¶

该模块定义标准 Python 编解码器 (编码器和解码器) 基类，并提供对内部 Python 编解码器注册的访问 (管理编解码器和错误处理的查找过程)。大多数标准编解码器都是文本编码，将文本编码成字节 (和将字节解码成文本)，但还提供将文本编码成文本和将字节编码成字节的编解码器。自定义编解码器可以在任意类型之间编码和解码，但一些模块特征限定具体使用采用文本编码或采用编解码器编码成 bytes .

模块定义了采用任何编解码器编码和解码的下列函数：

codecs. encode ( obj , encoding = 'utf-8' , errors = 'strict' ) ¶

编码 obj 使用注册编解码器为 encoding .

错误 may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that encoding errors raise ValueError (or a more codec specific subclass, such as UnicodeEncodeError ). Refer to 编解码器基类 for more information on codec error handling.

codecs. decode ( obj , encoding = 'utf-8' , errors = 'strict' ) ¶

解码 obj 使用注册编解码器为 encoding .

错误 may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that decoding errors raise ValueError (or a more codec specific subclass, such as UnicodeDecodeError ). Refer to 编解码器基类 for more information on codec error handling.

还可以直接查找每个编解码器的完整细节：

codecs. lookup ( encoding ) ¶

Looks up the codec info in the Python codec registry and returns a CodecInfo object as defined below.

Encodings are first looked up in the registry’s cache. If not found, the list of registered search functions is scanned. If no CodecInfo object is found, a LookupError is raised. Otherwise, the CodecInfo object is stored in the cache and returned to the caller.

class codecs. CodecInfo ( encode , decode , streamreader = None , streamwriter = None , incrementalencoder = None , incrementaldecoder = None , name = None ) ¶

Codec details when looking up the codec registry. The constructor arguments are stored in attributes of the same name:

name ¶: 编码的名称。

encode ¶
decode ¶: The stateless encoding and decoding functions. These must be functions or methods which have the same interface as the encode() and decode() methods of Codec instances (see Codec Interface ). The functions or methods are expected to work in a stateless mode.

incrementalencoder ¶
incrementaldecoder ¶: Incremental encoder and decoder classes or factory functions. These have to provide the interface defined by the base classes IncrementalEncoder and IncrementalDecoder , respectively. Incremental codecs can maintain state.

streamwriter ¶
streamreader ¶: Stream writer and reader classes or factory functions. These have to provide the interface defined by the base classes StreamWriter and StreamReader , respectively. Stream codecs can maintain state.

To simplify access to the various codec components, the module provides these additional functions which use lookup() for the codec lookup:

codecs. getencoder ( encoding ) ¶

Look up the codec for the given encoding and return its encoder function.

引发 LookupError 在找不到编码的情况下。

codecs. getdecoder ( encoding ) ¶

Look up the codec for the given encoding and return its decoder function.

引发 LookupError 在找不到编码的情况下。

codecs. getincrementalencoder ( encoding ) ¶

Look up the codec for the given encoding and return its incremental encoder class or factory function.

引发 LookupError in case the encoding cannot be found or the codec doesn’t support an incremental encoder.

codecs. getincrementaldecoder ( encoding ) ¶

Look up the codec for the given encoding and return its incremental decoder class or factory function.

引发 LookupError in case the encoding cannot be found or the codec doesn’t support an incremental decoder.

codecs. getreader ( encoding ) ¶

Look up the codec for the given encoding and return its StreamReader 类或工厂函数。

引发 LookupError 在找不到编码的情况下。

codecs. getwriter ( encoding ) ¶

Look up the codec for the given encoding and return its StreamWriter 类或工厂函数。

引发 LookupError 在找不到编码的情况下。

自定义编解码器可用于注册合适编解码器搜索功能：

codecs. register ( search_function ) ¶

Register a codec search function. Search functions are expected to take one argument, being the encoding name in all lower case letters with hyphens and spaces converted to underscores, and return a CodecInfo object. In case a search function cannot find a given encoding, it should return None .

3.9 版改变： Hyphens and spaces are converted to underscore.

codecs. unregister ( search_function ) ¶

Unregister a codec search function and clear the registry’s cache. If the search function is not registered, do nothing.

Added in version 3.10.

当内置 open() 和关联 io module are the recommended approach for working with encoded text files, this module provides additional utility functions and classes that allow the use of a wider range of codecs when working with binary files:

codecs. open ( filename , mode = 'r' , encoding = None , errors = 'strict' , buffering = -1 ) ¶

打开编码文件使用给定 mode 并返回实例化的 StreamReaderWriter ，提供透明编码/解码。默认文件模式为 'r' ，意味着以读取模式打开文件。

注意

若 encoding 不是 None , then the underlying encoded files are always opened in binary mode. No automatic conversion of '\n' is done on reading and writing. The mode argument may be any binary mode acceptable to the built-in open() 函数； 'b' is automatically added.

encoding specifies the encoding which is to be used for the file. Any encoding that encodes to and decodes from bytes is allowed, and the data types supported by the file methods depend on the codec used.

errors 可以给定以定义错误处理。默认为 'strict' which causes a ValueError to be raised in case an encoding error occurs.

buffering 拥有相同含义如内置 open() 函数。默认为 -1 意味着将使用默认缓冲大小。

3.11 版改变： The 'U' 模式被移除。

codecs. EncodedFile ( file , data_encoding , file_encoding = None , errors = 'strict' ) ¶

返回 StreamRecoder instance, a wrapped version of file which provides transparent transcoding. The original file is closed when the wrapped version is closed.

Data written to the wrapped file is decoded according to the given data_encoding and then written to the original file as bytes using file_encoding . Bytes read from the original file are decoded according to file_encoding , and the result is encoded using data_encoding .

若 file_encoding 不给定，默认为 data_encoding .

errors 可以给定以定义错误处理。默认为 'strict' , which causes ValueError to be raised in case an encoding error occurs.

codecs. iterencode ( iterator , encoding , errors = 'strict' , ** kwargs ) ¶

Uses an incremental encoder to iteratively encode the input provided by iterator . This function is a generator 。 errors argument (as well as any other keyword argument) is passed through to the incremental encoder.

This function requires that the codec accept text str objects to encode. Therefore it does not support bytes-to-bytes encoders such as base64_codec .

codecs. iterdecode ( iterator , encoding , errors = 'strict' , ** kwargs ) ¶

Uses an incremental decoder to iteratively decode the input provided by iterator . This function is a generator 。 errors argument (as well as any other keyword argument) is passed through to the incremental decoder.

此函数要求编解码器接受 bytes objects to decode. Therefore it does not support text-to-text encoders such as rot_13 , although rot_13 may be used equivalently with iterencode() .

The module also provides the following constants which are useful for reading and writing to platform dependent files:

codecs. BOM ¶
codecs. BOM_BE ¶
codecs. BOM_LE ¶
codecs. BOM_UTF8 ¶
codecs. BOM_UTF16 ¶
codecs. BOM_UTF16_BE ¶
codecs. BOM_UTF16_LE ¶
codecs. BOM_UTF32 ¶
codecs. BOM_UTF32_BE ¶
codecs. BOM_UTF32_LE ¶: These constants define various byte sequences, being Unicode byte order marks (BOMs) for several encodings. They are used in UTF-16 and UTF-32 data streams to indicate the byte order used, and in UTF-8 as a Unicode signature. BOM_UTF16 是 BOM_UTF16_BE or BOM_UTF16_LE depending on the platform’s native byte order, BOM 是别名化的 BOM_UTF16 , BOM_LE for BOM_UTF16_LE and BOM_BE for BOM_UTF16_BE . The others represent the BOM in UTF-8 and UTF-32 encodings.

编解码器基类 ¶

The codecs module defines a set of base classes which define the interfaces for working with codec objects, and can also be used as the basis for custom codec implementations.

Each codec has to define four interfaces to make it usable as codec in Python: stateless encoder, stateless decoder, stream reader and stream writer. The stream reader and writers typically reuse the stateless encoder/decoder to implement the file protocols. Codec authors also need to define how the codec will handle encoding and decoding errors.

错误处理程序 ¶

为简化并标准化错误处理，编解码器可以实现不同错误处理方案通过接受 errors 字符串自变量：

>>> 'German ß, ♬'.encode(encoding='ascii', errors='backslashreplace')
b'German \\xdf, \\u266c'
>>> 'German ß, ♬'.encode(encoding='ascii', errors='xmlcharrefreplace')
b'German &#223;, &#9836;'

下列错误处理程序可以用于所有 Python 标准编码编解码器：

值	含义
`'strict'`	引发 `UnicodeError` (or a subclass), this is the default. Implemented in `strict_errors()` .
`'ignore'`	Ignore the malformed data and continue without further notice. Implemented in `ignore_errors()` .
`'replace'`	Replace with a replacement marker. On encoding, use `?` (ASCII character). On decoding, use `�` (U+FFFD, the official REPLACEMENT CHARACTER). Implemented in `replace_errors()` .
`'backslashreplace'`	Replace with backslashed escape sequences. On encoding, use hexadecimal form of Unicode code point with formats `\xhh` `\uxxxx` `\Uxxxxxxxx` . On decoding, use hexadecimal form of byte value with format `\xhh` . Implemented in `backslashreplace_errors()` .
`'surrogateescape'`	On decoding, replace byte with individual surrogate code ranging from `U+DC80` to `U+DCFF` . This code will then be turned back into the same byte when the `'surrogateescape'` error handler is used when encoding the data. (See PEP 383 for more.)

下列错误处理程序只可应用于编码 (在文本编码 ):

值	含义
`'xmlcharrefreplace'`	Replace with XML/HTML numeric character reference, which is a decimal form of Unicode code point with format `&#num;` . Implemented in `xmlcharrefreplace_errors()` .
`'namereplace'`	替换采用 `\N{...}` escape sequences, what appears in the braces is the Name property from Unicode Character Database. Implemented in `namereplace_errors()` .

此外，以下错误处理程序是特定于给定编解码器的：

值	编解码器	含义
`'surrogatepass'`	utf-8, utf-16, utf-32, utf-16-be, utf-16-le, utf-32-be, utf-32-le	Allow encoding and decoding surrogate code point ( `U+D800` - `U+DFFF` ) as normal code point. Otherwise these codecs treat the presence of surrogate code point in `str` as an error.

Added in version 3.1: The 'surrogateescape' and 'surrogatepass' 错误处理程序。

3.4 版改变： The 'surrogatepass' 错误处理程序现在工作于 utf-16* 和 utf-32* 编解码器。

Added in version 3.5: The 'namereplace' 错误处理程序。

3.5 版改变： The 'backslashreplace' 错误处理程序现在工作于解码和翻译。

通过注册新的命名错误处理程序，可以扩展允许的值集：

codecs. register_error ( name , error_handler ) ¶

注册错误处理函数 error_handler 按名称 name 。 error_handler 自变量会被调用，在编码和解码期间若出错，当 name 被指定为错误参数。

For encoding, error_handler will be called with a UnicodeEncodeError instance, which contains information about the location of the error. The error handler must either raise this or a different exception, or return a tuple with a replacement for the unencodable part of the input and a position where encoding should continue. The replacement may be either str or bytes . If the replacement is bytes, the encoder will simply copy them into the output buffer. If the replacement is a string, the encoder will encode the replacement. Encoding continues on original input at the specified position. Negative position values will be treated as being relative to the end of the input string. If the resulting position is out of bound an IndexError 会被引发。

解码和翻译工作相似，除了 UnicodeDecodeError or UnicodeTranslateError will be passed to the handler and that the replacement from the error handler will be put into the output directly.

Previously registered error handlers (including the standard error handlers) can be looked up by name:

codecs. lookup_error ( name ) ¶

Return the error handler previously registered under the name name .

引发 LookupError 在无法找到处理程序的情况下。

以下标准错误处理程序还可用作模块级函数：

codecs. strict_errors ( exception ) ¶

实现 'strict' 错误处理。

Each encoding or decoding error raises a UnicodeError .

codecs. ignore_errors ( exception ) ¶

实现 'ignore' 错误处理。

Malformed data is ignored; encoding or decoding is continued without further notice.

codecs. replace_errors ( exception ) ¶

实现 'replace' 错误处理。

Substitutes ? (ASCII character) for encoding errors or � (U+FFFD, the official REPLACEMENT CHARACTER) for decoding errors.

codecs. backslashreplace_errors ( exception ) ¶

实现 'backslashreplace' 错误处理。

Malformed data is replaced by a backslashed escape sequence. On encoding, use the hexadecimal form of Unicode code point with formats \xhh \uxxxx \Uxxxxxxxx . On decoding, use the hexadecimal form of byte value with format \xhh .

3.5 版改变： Works with decoding and translating.

codecs. xmlcharrefreplace_errors ( exception ) ¶

实现 'xmlcharrefreplace' error handling (for encoding within 文本编码仅)。

The unencodable character is replaced by an appropriate XML/HTML numeric character reference, which is a decimal form of Unicode code point with format &#num; .

codecs. namereplace_errors ( exception ) ¶

实现 'namereplace' error handling (for encoding within 文本编码仅)。

The unencodable character is replaced by a \N{...} escape sequence. The set of characters that appear in the braces is the Name property from Unicode Character Database. For example, the German lowercase letter 'ß' will be converted to byte sequence \N{LATIN SMALL LETTER SHARP S} .

Added in version 3.5.

无状态编码和解码 ¶

The base Codec class defines these methods which also define the function interfaces of the stateless encoder and decoder:

class codecs. 编解码器 ¶

encode ( input , errors = 'strict' ) ¶

编码对象 input and returns a tuple (output object, length consumed). For instance, 文本编码 converts a string object to a bytes object using a particular character set encoding (e.g., cp1252 or iso-8859-1 ).

The errors argument defines the error handling to apply. It defaults to 'strict' 处理。

The method may not store state in the Codec 实例。使用 StreamWriter for codecs which have to keep state in order to make encoding efficient.

The encoder must be able to handle zero length input and return an empty object of the output object type in this situation.

decode ( input , errors = 'strict' ) ¶

解码对象 input and returns a tuple (output object, length consumed). For instance, for a 文本编码 , decoding converts a bytes object encoded using a particular character set encoding to a string object.

For text encodings and bytes-to-bytes codecs, input must be a bytes object or one which provides the read-only buffer interface – for example, buffer objects and memory mapped files.

The errors argument defines the error handling to apply. It defaults to 'strict' 处理。

The method may not store state in the Codec 实例。使用 StreamReader for codecs which have to keep state in order to make decoding efficient.

The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.

增量编码和解码 ¶

The IncrementalEncoder and IncrementalDecoder classes provide the basic interface for incremental encoding and decoding. Encoding/decoding the input isn’t done with one call to the stateless encoder/decoder function, but with multiple calls to the encode() / decode() method of the incremental encoder/decoder. The incremental encoder/decoder keeps track of the encoding/decoding process during method calls.

The joined output of calls to the encode() / decode() method is the same as if all the single inputs were joined into one, and this input was encoded/decoded with the stateless encoder/decoder.

IncrementalEncoder 对象 ¶

The IncrementalEncoder class is used for encoding an input in multiple steps. It defines the following methods which every incremental encoder must define in order to be compatible with the Python codec registry.

class codecs. IncrementalEncoder ( errors = 'strict' ) ¶

构造函数为 IncrementalEncoder 实例。

All incremental encoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.

The IncrementalEncoder may implement different error handling schemes by providing the errors keyword argument. See 错误处理程序了解可能值。

The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the IncrementalEncoder 对象。

encode ( object , final = False ) ¶: 编码 object (taking the current state of the encoder into account) and returns the resulting encoded object. If this is the last call to encode() final must be true (the default is false).

reset ( ) ¶: Reset the encoder to the initial state. The output is discarded: call .encode(object, final=True) , passing an empty byte or text string if necessary, to reset the encoder and to get the output.

getstate ( ) ¶: Return the current state of the encoder which must be an integer. The implementation should make sure that 0 is the most common state. (States that are more complicated than integers can be converted into an integer by marshaling/pickling the state and encoding the bytes of the resulting string into an integer.)

setstate ( state ) ¶: Set the state of the encoder to state . state must be an encoder state returned by getstate() .

IncrementalDecoder 对象 ¶

The IncrementalDecoder class is used for decoding an input in multiple steps. It defines the following methods which every incremental decoder must define in order to be compatible with the Python codec registry.

class codecs. IncrementalDecoder ( errors = 'strict' ) ¶

构造函数为 IncrementalDecoder 实例。

All incremental decoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.

The IncrementalDecoder may implement different error handling schemes by providing the errors keyword argument. See 错误处理程序了解可能值。

decode ( object , final = False ) ¶: 解码 object (taking the current state of the decoder into account) and returns the resulting decoded object. If this is the last call to decode() final must be true (the default is false). If final is true the decoder must decode the input completely and must flush all buffers. If this isn’t possible (e.g. because of incomplete byte sequences at the end of the input) it must initiate error handling just like in the stateless case (which might raise an exception).

reset ( ) ¶: 将解码器重置到初始状态。

getstate ( ) ¶: Return the current state of the decoder. This must be a tuple with two items, the first must be the buffer containing the still undecoded input. The second must be an integer and can be additional state info. (The implementation should make sure that 0 is the most common additional state info.) If this additional state info is 0 it must be possible to set the decoder to the state which has no input buffered and 0 as the additional state info, so that feeding the previously buffered input to the decoder returns it to the previous state without producing any output. (Additional state info that is more complicated than integers can be converted into an integer by marshaling/pickling the info and encoding the bytes of the resulting string into an integer.)

setstate ( state ) ¶: Set the state of the decoder to state . state must be a decoder state returned by getstate() .

流编码和解码 ¶

The StreamWriter and StreamReader classes provide generic working interfaces which can be used to implement new encoding submodules very easily. See encodings.utf_8 for an example of how this is done.

StreamWriter 对象 ¶

The StreamWriter 类是子类化的 Codec and defines the following methods which every stream writer must define in order to be compatible with the Python codec registry.

class codecs. StreamWriter ( stream , errors = 'strict' ) ¶

构造函数为 StreamWriter 实例。

All stream writers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.

The stream argument must be a file-like object open for writing text or binary data, as appropriate for the specific codec.

The StreamWriter may implement different error handling schemes by providing the errors keyword argument. See 错误处理程序 for the standard error handlers the underlying stream codec may support.

write ( object ) ¶: Writes the object’s contents encoded to the stream.

writelines ( list ) ¶: Writes the concatenated iterable of strings to the stream (possibly by reusing the write() method). Infinite or very large iterables are not supported. The standard bytes-to-bytes codecs do not support this method.

reset ( ) ¶

Resets the codec buffers used for keeping internal state.

Calling this method should ensure that the data on the output is put into a clean state that allows appending of new fresh data without having to rescan the whole stream to recover state.

In addition to the above methods, the StreamWriter must also inherit all other methods and attributes from the underlying stream.

StreamReader 对象 ¶

The StreamReader 类是子类化的 Codec and defines the following methods which every stream reader must define in order to be compatible with the Python codec registry.

class codecs. StreamReader ( stream , errors = 'strict' ) ¶

构造函数为 StreamReader 实例。

All stream readers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.

The stream argument must be a file-like object open for reading text or binary data, as appropriate for the specific codec.

The StreamReader may implement different error handling schemes by providing the errors keyword argument. See 错误处理程序 for the standard error handlers the underlying stream codec may support.

The set of allowed values for the errors argument can be extended with register_error() .

read ( size = -1 , chars = -1 , firstline = False ) ¶

Decodes data from the stream and returns the resulting object.

The chars argument indicates the number of decoded code points or bytes to return. The read() method will never return more data than requested, but it might return less, if there is not enough available.

The size argument indicates the approximate maximum number of encoded bytes or code points to read for decoding. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. This parameter is intended to prevent having to decode huge files in one step.

The firstline flag indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines.

The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.

readline ( size = None , keepends = True ) ¶

Read one line from the input stream and return the decoded data.

size , if given, is passed as size argument to the stream’s read() 方法。

若 keepends is false line-endings will be stripped from the lines returned.

readlines ( sizehint = None , keepends = True ) ¶

Read all lines available on the input stream and return them as a list of lines.

Line-endings are implemented using the codec’s decode() method and are included in the list entries if keepends 为 True。

sizehint , if given, is passed as the size argument to the stream’s read() 方法。

reset ( ) ¶

Resets the codec buffers used for keeping internal state.

Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.

In addition to the above methods, the StreamReader must also inherit all other methods and attributes from the underlying stream.

StreamReaderWriter 对象 ¶

The StreamReaderWriter is a convenience class that allows wrapping streams which work in both read and write modes.

The design is such that one can use the factory functions returned by the lookup() function to construct the instance.

class codecs. StreamReaderWriter ( stream , Reader , Writer , errors = 'strict' ) ¶: 创建 StreamReaderWriter 实例。 stream must be a file-like object. Reader and Writer must be factory functions or classes providing the StreamReader and StreamWriter interface resp. Error handling is done in the same way as defined for the stream readers and writers.

StreamReaderWriter instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream.

StreamWriter 对象 ¶

The StreamRecoder translates data from one encoding to another, which is sometimes useful when dealing with different encoding environments.

The design is such that one can use the factory functions returned by the lookup() function to construct the instance.

class codecs. StreamRecoder ( stream , encode , decode , Reader , Writer , errors = 'strict' ) ¶

创建 StreamRecoder instance which implements a two-way conversion: encode and decode work on the frontend — the data visible to code calling read() and write() ，而 Reader and Writer work on the backend — the data in stream .

You can use these objects to do transparent transcodings, e.g., from Latin-1 to UTF-8 and back.

The stream 自变量必须是像文件对象。

The encode and decode arguments must adhere to the Codec 接口。 Reader and Writer must be factory functions or classes providing objects of the StreamReader and StreamWriter interface respectively.

Error handling is done in the same way as defined for the stream readers and writers.

StreamRecoder instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream.

编码和 Unicode ¶

Strings are stored internally as sequences of code points in range U+0000 – U+10FFFF 。(见 PEP 393 for more details about the implementation.) Once a string object is used outside of CPU and memory, endianness and how these arrays are stored as bytes become an issue. As with other codecs, serialising a string into a sequence of bytes is known as encoding , and recreating the string from the sequence of bytes is known as decoding . There are a variety of different text serialisation codecs, which are collectivity referred to as 文本编码 .

The simplest text encoding (called 'latin-1' or 'iso-8859-1' ) maps the code points 0–255 to the bytes 0x0 – 0xff , which means that a string object that contains code points above U+00FF can’t be encoded with this codec. Doing so will raise a UnicodeEncodeError that looks like the following (although the details of the error message may differ): UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in position 3: ordinal not in range(256) .

There’s another group of encodings (the so called charmap encodings) that choose a different subset of all Unicode code points and how these code points are mapped to the bytes 0x0 – 0xff . To see how this is done simply open e.g. encodings/cp1252.py (which is an encoding that is used primarily on Windows). There’s a string constant with 256 characters that shows you which character is mapped to which byte value.

All of these encodings can only encode 256 of the 1114112 code points defined in Unicode. A simple and straightforward way that can store each Unicode code point, is to store each code point as four consecutive bytes. There are two possibilities: store the bytes in big endian or in little endian order. These two encodings are called UTF-32-BE and UTF-32-LE respectively. Their disadvantage is that if e.g. you use UTF-32-BE on a little endian machine you will always have to swap bytes on encoding and decoding. UTF-32 avoids this problem: bytes will always be in natural endianness. When these bytes are read by a CPU with a different endianness, then bytes have to be swapped though. To be able to detect the endianness of a UTF-16 or UTF-32 byte sequence, there’s the so called BOM (“Byte Order Mark”). This is the Unicode character U+FEFF . This character can be prepended to every UTF-16 or UTF-32 byte sequence. The byte swapped version of this character ( 0xFFFE ) is an illegal character that may not appear in a Unicode text. So when the first character in a UTF-16 or UTF-32 byte sequence appears to be a U+FFFE the bytes have to be swapped on decoding. Unfortunately the character U+FEFF had a second purpose as a ZERO WIDTH NO-BREAK SPACE : a character that has no width and doesn’t allow a word to be split. It can e.g. be used to give hints to a ligature algorithm. With Unicode 4.0 using U+FEFF 作为 ZERO WIDTH NO-BREAK SPACE has been deprecated (with U+2060 ( WORD JOINER ) assuming this role). Nevertheless Unicode software still must be able to handle U+FEFF in both roles: as a BOM it’s a device to determine the storage layout of the encoded bytes, and vanishes once the byte sequence has been decoded into a string; as a ZERO WIDTH NO-BREAK SPACE it’s a normal character that will be decoded like any other.

There’s another encoding that is able to encode the full range of Unicode characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two parts: marker bits (the most significant bits) and payload bits. The marker bits are a sequence of zero to four 1 bits followed by a 0 bit. Unicode characters are encoded like this (with x being payload bits, which when concatenated give the Unicode character):

范围	编码
`U-00000000` … `U-0000007F`	0xxxxxxx
`U-00000080` … `U-000007FF`	110xxxxx 10xxxxxx
`U-00000800` … `U-0000FFFF`	1110xxxx 10xxxxxx 10xxxxxx
`U-00010000` … `U-0010FFFF`	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

The least significant bit of the Unicode character is the rightmost x bit.

As UTF-8 is an 8-bit encoding no BOM is required and any U+FEFF character in the decoded string (even if it’s the first character) is treated as a ZERO WIDTH NO-BREAK SPACE .

Without external information it’s impossible to reliably determine which encoding was used for encoding a string. Each charmap encoding can decode any random byte sequence. However that’s not possible with UTF-8, as UTF-8 byte sequences have a structure that doesn’t allow arbitrary byte sequences. To increase the reliability with which a UTF-8 encoding can be detected, Microsoft invented a variant of UTF-8 (that Python calls "utf-8-sig" ) for its Notepad program: Before any of the Unicode characters is written to the file, a UTF-8 encoded BOM (which looks like this as a byte sequence: 0xef , 0xbb , 0xbf ) is written. As it’s rather improbable that any charmap encoded file starts with these byte values (which would e.g. map to

LATIN SMALL LETTER I WITH DIAERESIS

RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK

INVERTED QUESTION MARK

in iso-8859-1), this increases the probability that a utf-8-sig encoding can be correctly guessed from the byte sequence. So here the BOM is not used to be able to determine the byte order used for generating the byte sequence, but as a signature that helps in guessing the encoding. On encoding the utf-8-sig codec will write 0xef , 0xbb , 0xbf as the first three bytes to the file. On decoding utf-8-sig will skip those three bytes if they appear as the first three bytes in the file. In UTF-8, the use of the BOM is discouraged and should generally be avoided.

标准编码 ¶

Python comes with a number of codecs built-in, either implemented as C functions or with dictionaries as mapping tables. The following table lists the codecs by name, together with a few common aliases, and the languages for which the encoding is likely used. Neither the list of aliases nor the list of languages is meant to be exhaustive. Notice that spelling alternatives that only differ in case or use a hyphen instead of an underscore are also valid aliases; therefore, e.g. 'utf-8' is a valid alias for the 'utf_8' 编解码器。

CPython 实现细节： Some common encodings can bypass the codecs lookup machinery to improve performance. These optimization opportunities are only recognized by CPython for a limited set of (case insensitive) aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, iso8859-1, mbcs (Windows only), ascii, us-ascii, utf-16, utf16, utf-32, utf32, and the same using underscores instead of dashes. Using alternative aliases for these encodings may result in slower execution.

3.6 版改变： Optimization opportunity recognized for us-ascii.

Many of the character sets support the same languages. They vary in individual characters (e.g. whether the EURO SIGN is supported or not), and in the assignment of characters to code positions. For the European languages in particular, the following variants typically exist:

ISO 8859 代码集
a Microsoft Windows code page, which is typically derived from an 8859 codeset, but replaces control characters with additional graphic characters
IBM EBCDIC 代码页
IBM PC 代码页，兼容 ASCII

编解码器	别名	语言
ascii	646, us-ascii	English
big5	big5-tw, csbig5	繁体中文
big5hkscs	big5-hkscs, hkscs	繁体中文
cp037	IBM037, IBM039	English
cp273	273, IBM273, csIBM273	德语 Added in version 3.4.
cp424	EBCDIC-CP-HE, IBM424	希伯来语
cp437	437, IBM437	English
cp500	EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500	西欧
cp720		阿拉伯语
cp737		希腊语
cp775	IBM775	波罗的语
cp850	850, IBM850	西欧
cp852	852, IBM852	中东欧
cp855	855, IBM855	Bulgarian, Byelorussian, Macedonian, Russian, Serbian
cp856		希伯来语
cp857	857, IBM857	土耳其语
cp858	858, IBM858	西欧
cp860	860, IBM860	葡萄牙语
cp861	861, CP-IS, IBM861	冰岛语
cp862	862, IBM862	希伯来语
cp863	863, IBM863	加拿大
cp864	IBM864	阿拉伯语
cp865	865, IBM865	Danish, Norwegian
cp866	866, IBM866	俄语
cp869	869, CP-GR, IBM869	希腊语
cp874		泰语
cp875		希腊语
cp932	932, ms932, mskanji, ms-kanji	日语
cp949	949, ms949, uhc	韩语
cp950	950, ms950	繁体中文
cp1006		乌尔都语
cp1026	ibm1026	土耳其语
cp1125	1125, ibm1125, cp866u, ruscii	乌克兰语 Added in version 3.4.
cp1140	ibm1140	西欧
cp1250	windows-1250	中东欧
cp1251	windows-1251	Bulgarian, Byelorussian, Macedonian, Russian, Serbian
cp1252	windows-1252	西欧
cp1253	windows-1253	希腊语
cp1254	windows-1254	土耳其语
cp1255	windows-1255	希伯来语
cp1256	windows-1256	阿拉伯语
cp1257	windows-1257	波罗的语
cp1258	windows-1258	越南语
euc_jp	eucjp, ujis, u-jis	日语
euc_jis_2004	jisx0213, eucjis2004	日语
euc_jisx0213	eucjisx0213	日语
euc_kr	euckr, korean, ksc5601, ks_c-5601, ks_c-5601-1987, ksx1001, ks_x-1001	韩语
gb2312	chinese, csiso58gb231280, euc-cn, euccn, eucgb2312-cn, gb2312-1980, gb2312-80, iso-ir-58	简体中文
gbk	936, cp936, ms936	Unified Chinese
gb18030	gb18030-2000	Unified Chinese
hz	hzgb, hz-gb, hz-gb-2312	简体中文
iso2022_jp	csiso2022jp, iso2022jp, iso-2022-jp	日语
iso2022_jp_1	iso2022jp-1, iso-2022-jp-1	日语
iso2022_jp_2	iso2022jp-2, iso-2022-jp-2	Japanese, Korean, Simplified Chinese, Western Europe, Greek
iso2022_jp_2004	iso2022jp-2004, iso-2022-jp-2004	日语
iso2022_jp_3	iso2022jp-3, iso-2022-jp-3	日语
iso2022_jp_ext	iso2022jp-ext, iso-2022-jp-ext	日语
iso2022_kr	csiso2022kr, iso2022kr, iso-2022-kr	韩语
latin_1	iso-8859-1, iso8859-1, 8859, cp819, latin, latin1, L1	西欧
iso8859_2	iso-8859-2, latin2, L2	中东欧
iso8859_3	iso-8859-3, latin3, L3	Esperanto, Maltese
iso8859_4	iso-8859-4, latin4, L4	波罗的语
iso8859_5	iso-8859-5, cyrillic	Bulgarian, Byelorussian, Macedonian, Russian, Serbian
iso8859_6	iso-8859-6, arabic	阿拉伯语
iso8859_7	iso-8859-7, greek, greek8	希腊语
iso8859_8	iso-8859-8, hebrew	希伯来语
iso8859_9	iso-8859-9, latin5, L5	土耳其语
iso8859_10	iso-8859-10, latin6, L6	Nordic languages
iso8859_11	iso-8859-11, thai	泰语
iso8859_13	iso-8859-13, latin7, L7	波罗的语
iso8859_14	iso-8859-14, latin8, L8	Celtic languages
iso8859_15	iso-8859-15, latin9, L9	西欧
iso8859_16	iso-8859-16, latin10, L10	东南欧
johab	cp1361, ms1361	韩语
koi8_r		俄语
koi8_t		Tajik Added in version 3.5.
koi8_u		乌克兰语
kz1048	kz_1048, strk1048_2002, rk1048	Kazakh Added in version 3.5.
mac_cyrillic	maccyrillic	Bulgarian, Byelorussian, Macedonian, Russian, Serbian
mac_greek	macgreek	希腊语
mac_iceland	maciceland	冰岛语
mac_latin2	maclatin2, maccentraleurope, mac_centeuro	中东欧
mac_roman	macroman, macintosh	西欧
mac_turkish	macturkish	土耳其语
ptcp154	csptcp154, pt154, cp154, cyrillic-asian	Kazakh
shift_jis	csshiftjis, shiftjis, sjis, s_jis	日语
shift_jis_2004	shiftjis2004, sjis_2004, sjis2004	日语
shift_jisx0213	shiftjisx0213, sjisx0213, s_jisx0213	日语
utf_32	U32, utf32	所有语言
utf_32_be	UTF-32BE	所有语言
utf_32_le	UTF-32LE	所有语言
utf_16	U16, utf16	所有语言
utf_16_be	UTF-16BE	所有语言
utf_16_le	UTF-16LE	所有语言
utf_7	U7, unicode-1-1-utf-7	所有语言
utf_8	U8, UTF, utf8, cp65001	所有语言
utf_8_sig		所有语言

3.4 版改变： The utf-16* and utf-32* encoders no longer allow surrogate code points ( U+D800 – U+DFFF ) to be encoded. The utf-32* decoders no longer decode byte sequences that correspond to surrogate code points.

3.8 版改变： cp65001 现在是别名化的 utf_8 .

Python 特定编码 ¶

A number of predefined codecs are specific to Python, so their codec names have no meaning outside Python. These are listed in the tables below based on the expected input and output types (note that while text encodings are the most common use case for codecs, the underlying codec infrastructure supports arbitrary data transforms rather than just text encodings). For asymmetric codecs, the stated meaning describes the encoding direction.

文本编码 ¶

以下编解码器提供 str to bytes 编码和像字节对象 to str 解码，类似 Unicode 文本编码。

编解码器	别名	含义
idna		实现 RFC 3490 ，另请参阅 `encodings.idna` . Only `errors='strict'` is supported.
mbcs	ansi, dbcs	Windows only: Encode the operand according to the ANSI codepage (CP_ACP).
oem		Windows only: Encode the operand according to the OEM codepage (CP_OEMCP). Added in version 3.6.
palmos		Encoding of PalmOS 3.5.
punycode		实现 RFC 3492 . Stateful codecs are not supported.
raw_unicode_escape		Latin-1 encoding with `\uXXXX` and `\UXXXXXXXX` for other code points. Existing backslashes are not escaped in any way. It is used in the Python pickle protocol.
undefined		Raise an exception for all conversions, even empty strings. The error handler is ignored.
unicode_escape		Encoding suitable as the contents of a Unicode literal in ASCII-encoded Python source code, except that quotes are not escaped. Decode from Latin-1 source code. Beware that Python source code actually uses UTF-8 by default.

3.8 版改变：移除 unicode_internal 编解码器。

二进制变换 ¶

The following codecs provide binary transforms: 像字节对象 to bytes mappings. They are not supported by bytes.decode() (which only produces str 输出)。

编解码器	别名	含义	编码器/解码器
base64_codec [ 1 ]	base64, base_64	Convert the operand to multiline MIME base64 (the result always includes a trailing `'\n'` ). 3.4 版改变： accepts any 像字节对象 as input for encoding and decoding	`base64.encodebytes()` / `base64.decodebytes()`
bz2_codec	bz2	Compress the operand using bz2.	`bz2.compress()` / `bz2.decompress()`
hex_codec	hex	Convert the operand to hexadecimal representation, with two digits per byte.	`binascii.b2a_hex()` / `binascii.a2b_hex()`
quopri_codec	quopri, quotedprintable, quoted_printable	Convert the operand to MIME quoted printable.	`quopri.encode()` with `quotetabs=True` / `quopri.decode()`
uu_codec	uu	Convert the operand using uuencode.	`uu.encode()` / `uu.decode()` (Note: `uu` is deprecated.)
zlib_codec	zip, zlib	Compress the operand using gzip.	`zlib.compress()` / `zlib.decompress()`

Added in version 3.2: 二进制变换的还原。

3.4 版改变：二进制变换别名的还原。

文本变换 ¶

以下编解码器提供文本变换： str to str mapping. It is not supported by str.encode() (which only produces bytes 输出)。

编解码器	别名	含义
rot_13	rot13	Return the Caesar-cypher encryption of the operand.

Added in version 3.2: Restoration of the rot_13 文本变换。

3.4 版改变： Restoration of the rot13 别名。

`encodings.idna` — 应用程序中的国际化域名 ¶

本模块实现 RFC 3490 (Internationalized Domain Names in Applications) and RFC 3492 (Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)). It builds upon the punycode 编码和 stringprep .

If you need the IDNA 2008 standard from RFC 5891 and RFC 5895 , use the third-party idna 模块。

These RFCs together define a protocol to support non-ASCII characters in domain names. A domain name containing non-ASCII characters (such as www.Alliancefrançaise.nu ) is converted into an ASCII-compatible encoding (ACE, such as www.xn--alliancefranaise-npb.nu ). The ACE form of the domain name is then used in all places where arbitrary characters are not allowed by the protocol, such as DNS queries, HTTP Host fields, and so on. This conversion is carried out in the application; if possible invisible to the user: The application should transparently convert Unicode domain labels to IDNA on the wire, and convert back ACE labels to Unicode before presenting them to the user.

Python supports this conversion in several ways: the idna codec performs conversion between Unicode and ACE, separating an input string into labels based on the separator characters defined in section 3.1 of RFC 3490 and converting each label to ACE as required, and conversely separating an input byte string into labels based on the . separator and converting any ACE labels found into unicode. Furthermore, the socket module transparently converts Unicode host names to ACE, so that applications need not be concerned about converting host names themselves when they pass them to the socket module. On top of that, modules that have host names as function parameters, such as http.client and ftplib , accept Unicode host names ( http.client then also transparently sends an IDNA hostname in the Host field if it sends that field at all).

When receiving host names from the wire (such as in reverse name lookup), no automatic conversion to Unicode is performed: applications wishing to present such host names to the user should decode them to Unicode.

模块 encodings.idna also implements the nameprep procedure, which performs certain normalizations on host names, to achieve case-insensitivity of international domain names, and to unify similar characters. The nameprep functions can be used directly if desired.

encodings.idna. nameprep ( label ) ¶: Return the nameprepped version of label . The implementation currently assumes query strings, so AllowUnassigned 为 True。

encodings.idna. ToASCII ( label ) ¶: Convert a label to ASCII, as specified in RFC 3490 . UseSTD3ASCIIRules is assumed to be false.

encodings.idna. ToUnicode ( label ) ¶: Convert a label to Unicode, as specified in RFC 3490 .

`encodings.mbcs` — Windows ANSI 代码页 ¶

This module implements the ANSI codepage (CP_ACP).

可用性：Windows。

3.2 版改变：在 3.2 之前， errors 自变量被忽略； 'replace' 始终用于编码，和 'ignore' 以解码。

3.3 版改变：支持任何错误处理程序。

`encodings.utf_8_sig` — 具有 BOM (字节序标记) 签名的 UTF-8 编解码器 ¶

This module implements a variant of the UTF-8 codec. On encoding, a UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this is only done once (on the first write to the byte stream). On decoding, an optional UTF-8 encoded BOM at the start of the data will be skipped.