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
, which encode text to bytes, but there are also codecs provided that encode text to text, and bytes to bytes. Custom codecs may encode and decode between arbitrary types, but some module features are restricted to use specifically with
文本编码
, or with codecs that encode to
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
[
,
errors
]
]
)
¶
编码
obj
使用注册编解码器为
encoding
. The default encoding is
utf-8
.
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
[
,
errors
]
]
)
¶
解码
obj
使用注册编解码器为
encoding
. The default encoding is
utf-8
.
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.
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:
名称
¶
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 class or factory function.
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 class or factory function.
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, and return a
CodecInfo
object. In case a search function cannot find a given encoding, it should return
None
.
注意
Search function registration is not currently reversible, which may cause problems in some cases, such as unit testing or module reloading.
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
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()
function. It defaults to line buffered.
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.
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.
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.
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.
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 string argument. The following string values are defined and implemented by all standard Python codecs:
| 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()
.
|
以下错误处理程序仅适用于 文本编码 :
| 值 | 含义 |
|---|---|
'replace'
|
Replace with a suitable replacement
marker; Python will use the official
U+FFFD
REPLACEMENT CHARACTER for the
built-in codecs on decoding, and ‘?’ on
encoding. Implemented in
replace_errors()
.
|
'xmlcharrefreplace'
|
Replace with the appropriate XML character
reference (only for encoding). Implemented
in
xmlcharrefreplace_errors()
.
|
'backslashreplace'
|
Replace with backslashed escape sequences
(only for encoding). 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.)
|
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 of surrogate codes. These codecs normally treat the presence of surrogates as an error. |
3.1 版新增：
The
'surrogateescape'
and
'surrogatepass'
错误处理程序。
3.4 版改变：
The
'surrogatepass'
error handlers now works with utf-16* and utf-32* codecs.
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：每一编码或解码错误引发
UnicodeError
.
codecs.
replace_errors
(
exception
)
¶
实现
'replace'
错误处理 (为
文本编码
only): substitutes
'?'
for encoding errors (to be encoded by the codec), and
'\ufffd'
(the Unicode replacement character) for decoding errors.
codecs.
ignore_errors
(
exception
)
¶
实现
'ignore'
error handling: malformed data is ignored and encoding or decoding is continued without further notice.
codecs.
xmlcharrefreplace_errors
(
exception
)
¶
实现
'xmlcharrefreplace'
错误处理 (为编码采用
文本编码
only): the unencodable character is replaced by an appropriate XML character reference.
codecs.
backslashreplace_errors
(
exception
)
¶
实现
'backslashreplace'
错误处理 (为编码采用
文本编码
only): the unencodable character is replaced by a backslashed escape sequence.
The base
Codec
class defines these methods which also define the function interfaces of the stateless encoder and decoder:
Codec.
encode
(
input
[
,
errors
]
)
¶
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.
Codec.
decode
(
input
[
,
errors
]
)
¶
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.
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.
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.
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
]
)
¶
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.
IncrementalEncoder.
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).
IncrementalEncoder.
setstate
(
state
)
¶
Set the state of the encoder to
state
.
state
must be an encoder state returned by
getstate()
.
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.
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。
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
IncrementalDecoder
对象。
decode
(
object
[
,
final
]
)
¶
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 encoder to
state
.
state
must be a decoder state returned by
getstate()
.
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.
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.
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.
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
StreamWriter
对象。
write
(
object
)
¶
Writes the object’s contents encoded to the stream.
writelines
(
list
)
¶
Writes the concatenated list of strings to the stream (possibly by reusing the
write()
method). The standard bytes-to-bytes codecs do not support this method.
reset
(
)
¶
Flushes and resets the codec buffers used for keeping 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.
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.
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
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
StreamReader
对象。
The set of allowed values for the
errors
argument can be extended with
register_error()
.
read
(
[
size
[
,
chars
[
,
firstline
]
]
]
)
¶
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
[
,
keepends
]
]
)
¶
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
[
,
keepends
]
]
)
¶
Read all lines available on the input stream and return them as a list of lines.
Line-endings are implemented using the codec’s decoder 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 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.
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.
codecs.
StreamReaderWriter
(
stream
,
Reader
,
Writer
,
errors
)
¶
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.
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.
codecs.
StreamRecoder
(
stream
,
encode
,
decode
,
Reader
,
Writer
,
errors
)
¶
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 from e.g. 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.
Strings are stored internally as sequences of code points in range
0x0
-
0x10FFFF
。(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 an
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 encoding 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 2.5 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
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.
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 aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, mbcs (Windows only), ascii, utf-16, and utf-32. Using alternative spellings for these encodings may result in slower execution.
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:
| 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 3.4 版新增。 |
| 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 3.4 版新增。 |
| 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 |
| cp65001 |
Windows only: Windows UTF-8 (
3.3 版新增。 |
|
| 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 | West Europe |
| 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_u | 乌克兰语 | |
| mac_cyrillic | maccyrillic | Bulgarian, Byelorussian, Macedonian, Russian, Serbian |
| mac_greek | macgreek | 希腊语 |
| mac_iceland | maciceland | 冰岛语 |
| mac_latin2 | maclatin2, maccentraleurope | 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 | 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.
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 purpose describes the encoding direction.
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 | 目的 |
|---|---|---|
| idna |
实现
RFC 3490
,
see also
encodings.idna
.
仅
errors='strict'
is supported.
|
|
| mbcs | dbcs | Windows only: Encode operand according to the ANSI codepage (CP_ACP) |
| 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. Decodes from Latin-1 source code. Beware that Python source code actually uses UTF-8 在默认情况下。 | |
| unicode_internal |
Return the internal representation of the operand. Stateful codecs are not supported. 从 3.3 版起弃用： This representation is obsoleted by PEP 393 . |
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 | 目的 | 编码器/解码器 |
|---|---|---|---|
| base64_codec [1] | base64, base_64 |
Convert operand to multiline MIME base64 (the result always includes a trailing
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 operand to hexadecimal representation, with two digits per byte |
binascii.b2a_hex()
/
binascii.a2b_hex()
|
| quopri_codec | quopri, quotedprintable, quoted_printable | Convert operand to MIME quoted printable |
quopri.encode()
with
quotetabs=True
/
quopri.decode()
|
| uu_codec | uu | Convert the operand using uuencode |
uu.encode()
/
uu.decode()
|
| zlib_codec | zip, zlib | Compress the operand using gzip |
zlib.compress()
/
zlib.decompress()
|
| [1] |
除了
像字节对象
,
'base64_codec'
还接受仅 ASCII 实例的
str
for
decoding
|
3.2 版新增： 二进制变换的还原。
3.4 版改变： 二进制变换别名的还原。
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 | 目的 |
|---|---|---|
| rot_13 | rot13 | Returns the Caesar-cypher encryption of the operand |
3.2 版新增：
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
.
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
(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.mbcs
— Windows ANSI 代码页
¶
CP_ACP (根据 ANSI 代码页) 编码操作数。
可用性：仅 Windows。
3.3 版改变： 支持任何错误处理程序。
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。
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). For decoding an optional UTF-8 encoded BOM at the start of the data will be skipped.