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Issue 19548: update codecs module documentation 

- clarified the distinction between text encodings and other codecs
- clarified relationship with builtin open and the io module
- consolidated documentation of error handlers into one section
- clarified type constraints of some behaviours
- added tests for some of the new statements in the docs
This commit is contained in:
Nick Coghlan 2015-01-07 00:22:00 +10:00
parent fcfed19913
commit b9fdb7a452
9 changed files with 426 additions and 372 deletions
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5
Doc/glossary.rst
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@ -820,10 +820,13 @@ Glossary
:meth:`~collections.somenamedtuple._asdict`. Examples of struct sequences :meth:`~collections.somenamedtuple._asdict`. Examples of struct sequences
include :data:`sys.float_info` and the return value of :func:`os.stat`. include :data:`sys.float_info` and the return value of :func:`os.stat`.
text encoding
A codec which encodes Unicode strings to bytes.
text file text file
A :term:`file object` able to read and write :class:`str` objects. A :term:`file object` able to read and write :class:`str` objects.
Often, a text file actually accesses a byte-oriented datastream Often, a text file actually accesses a byte-oriented datastream
and handles the text encoding automatically. and handles the :term:`text encoding` automatically.
.. seealso:: .. seealso::
A :term:`binary file` reads and write :class:`bytes` objects. A :term:`binary file` reads and write :class:`bytes` objects.

648
Doc/library/codecs.rst
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@ -17,10 +17,17 @@
pair: stackable; streams pair: stackable; streams
This module defines base classes for standard Python codecs (encoders and This module defines base classes for standard Python codecs (encoders and
decoders) and provides access to the internal Python codec registry which decoders) and provides access to the internal Python codec registry, which
manages the codec and error handling lookup process. manages the codec and error handling lookup process. Most standard codecs
are :term:`text encodings <text encoding>`, 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
:term:`text encodings <text encoding>`, or with codecs that encode to
:class:`bytes`.
It defines the following functions: The module defines the following functions for encoding and decoding with
any codec:
.. function:: encode(obj, [encoding[, errors]]) .. function:: encode(obj, [encoding[, errors]])
@ -28,7 +35,7 @@ It defines the following functions:
encoding is ``utf-8``. encoding is ``utf-8``.
*Errors* may be given to set the desired error handling scheme. The *Errors* may be given to set the desired error handling scheme. The
default error handler is ``strict`` meaning that encoding errors raise default error handler is ``'strict'`` meaning that encoding errors raise
:exc:`ValueError` (or a more codec specific subclass, such as :exc:`ValueError` (or a more codec specific subclass, such as
:exc:`UnicodeEncodeError`). Refer to :ref:`codec-base-classes` for more :exc:`UnicodeEncodeError`). Refer to :ref:`codec-base-classes` for more
information on codec error handling. information on codec error handling.
@ -39,90 +46,63 @@ It defines the following functions:
encoding is ``utf-8``. encoding is ``utf-8``.
*Errors* may be given to set the desired error handling scheme. The *Errors* may be given to set the desired error handling scheme. The
default error handler is ``strict`` meaning that decoding errors raise default error handler is ``'strict'`` meaning that decoding errors raise
:exc:`ValueError` (or a more codec specific subclass, such as :exc:`ValueError` (or a more codec specific subclass, such as
:exc:`UnicodeDecodeError`). Refer to :ref:`codec-base-classes` for more :exc:`UnicodeDecodeError`). Refer to :ref:`codec-base-classes` for more
information on codec error handling. information on codec error handling.
.. function:: register(search_function) The full details for each codec can also be looked up directly:
Register a codec search function. Search functions are expected to take one
argument, the encoding name in all lower case letters, and return a
:class:`CodecInfo` object having the following attributes:
* ``name`` The name of the encoding;
* ``encode`` The stateless encoding function;
* ``decode`` The stateless decoding function;
* ``incrementalencoder`` An incremental encoder class or factory function;
* ``incrementaldecoder`` An incremental decoder class or factory function;
* ``streamwriter`` A stream writer class or factory function;
* ``streamreader`` A stream reader class or factory function.
The various functions or classes take the following arguments:
*encode* and *decode*: These must be functions or methods which have the same
interface as the :meth:`~Codec.encode`/:meth:`~Codec.decode` methods of Codec
instances (see :ref:`Codec Interface <codec-objects>`). The functions/methods
are expected to work in a stateless mode.
*incrementalencoder* and *incrementaldecoder*: These have to be factory
functions providing the following interface:
``factory(errors='strict')``
The factory functions must return objects providing the interfaces defined by
the base classes :class:`IncrementalEncoder` and :class:`IncrementalDecoder`,
respectively. Incremental codecs can maintain state.
*streamreader* and *streamwriter*: These have to be factory functions providing
the following interface:
``factory(stream, errors='strict')``
The factory functions must return objects providing the interfaces defined by
the base classes :class:`StreamReader` and :class:`StreamWriter`, respectively.
Stream codecs can maintain state.
Possible values for errors are
* ``'strict'``: raise an exception in case of an encoding error
* ``'replace'``: replace malformed data with a suitable replacement marker,
such as ``'?'`` or ``'\ufffd'``
* ``'ignore'``: ignore malformed data and continue without further notice
* ``'xmlcharrefreplace'``: replace with the appropriate XML character
reference (for encoding only)
* ``'backslashreplace'``: replace with backslashed escape sequences (for
encoding only)
* ``'surrogateescape'``: on decoding, replace with code points in the Unicode
Private Use Area ranging from U+DC80 to U+DCFF. These private code
points will then be turned back into the same bytes when the
``surrogateescape`` error handler is used when encoding the data.
(See :pep:`383` for more.)
as well as any other error handling name defined via :func:`register_error`.
In case a search function cannot find a given encoding, it should return
``None``.
.. function:: lookup(encoding) .. function:: lookup(encoding)
Looks up the codec info in the Python codec registry and returns a Looks up the codec info in the Python codec registry and returns a
:class:`CodecInfo` object as defined above. :class:`CodecInfo` object as defined below.
Encodings are first looked up in the registry's cache. If not found, the list of Encodings are first looked up in the registry's cache. If not found, the list of
registered search functions is scanned. If no :class:`CodecInfo` object is registered search functions is scanned. If no :class:`CodecInfo` object is
found, a :exc:`LookupError` is raised. Otherwise, the :class:`CodecInfo` object found, a :exc:`LookupError` is raised. Otherwise, the :class:`CodecInfo` object
is stored in the cache and returned to the caller. is stored in the cache and returned to the caller.
To simplify access to the various codecs, the module provides these additional .. class:: CodecInfo(encode, decode, streamreader=None, streamwriter=None, incrementalencoder=None, incrementaldecoder=None, name=None)
functions which use :func:`lookup` for the codec lookup:
Codec details when looking up the codec registry. The constructor
arguments are stored in attributes of the same name:
.. attribute:: name
The name of the encoding.
.. attribute:: encode
decode
The stateless encoding and decoding functions. These must be
functions or methods which have the same interface as
the :meth:`~Codec.encode` and :meth:`~Codec.decode` methods of Codec
instances (see :ref:`Codec Interface <codec-objects>`).
The functions or methods are expected to work in a stateless mode.
.. attribute:: incrementalencoder
incrementaldecoder
Incremental encoder and decoder classes or factory functions.
These have to provide the interface defined by the base classes
:class:`IncrementalEncoder` and :class:`IncrementalDecoder`,
respectively. Incremental codecs can maintain state.
.. attribute:: streamwriter
streamreader
Stream writer and reader classes or factory functions. These have to
provide the interface defined by the base classes
:class:`StreamWriter` and :class:`StreamReader`, respectively.
Stream codecs can maintain state.
To simplify access to the various codec components, the module provides
these additional functions which use :func:`lookup` for the codec lookup:
.. function:: getencoder(encoding) .. function:: getencoder(encoding)
@ -172,90 +152,43 @@ functions which use :func:`lookup` for the codec lookup:
Raises a :exc:`LookupError` in case the encoding cannot be found. Raises a :exc:`LookupError` in case the encoding cannot be found.
Custom codecs are made available by registering a suitable codec search
function:
.. function:: register_error(name, error_handler) .. function:: register(search_function)
Register the error handling function *error_handler* under the name *name*. Register a codec search function. Search functions are expected to take one
*error_handler* will be called during encoding and decoding in case of an error, argument, being the encoding name in all lower case letters, and return a
when *name* is specified as the errors parameter. :class:`CodecInfo` object. In case a search function cannot find
a given encoding, it should return ``None``.
For encoding *error_handler* will be called with a :exc:`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 :class:`str` or
:class:`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 :exc:`IndexError` will be raised.
Decoding and translating works similar, except :exc:`UnicodeDecodeError` or
:exc:`UnicodeTranslateError` will be passed to the handler and that the
replacement from the error handler will be put into the output directly.
.. function:: lookup_error(name)
Return the error handler previously registered under the name *name*.
Raises a :exc:`LookupError` in case the handler cannot be found.
.. function:: strict_errors(exception)
Implements the ``strict`` error handling: each encoding or decoding error
raises a :exc:`UnicodeError`.
.. function:: replace_errors(exception)
Implements the ``replace`` error handling: malformed data is replaced with a
suitable replacement character such as ``'?'`` in bytestrings and
``'\ufffd'`` in Unicode strings.
.. function:: ignore_errors(exception)
Implements the ``ignore`` error handling: malformed data is ignored and
encoding or decoding is continued without further notice.
.. function:: xmlcharrefreplace_errors(exception)
Implements the ``xmlcharrefreplace`` error handling (for encoding only): the
unencodable character is replaced by an appropriate XML character reference.
.. function:: backslashreplace_errors(exception)
Implements the ``backslashreplace`` error handling (for encoding only): the
unencodable character is replaced by a backslashed escape sequence.
To simplify working with encoded files or stream, the module also defines these
utility functions:
.. function:: open(filename, mode[, encoding[, errors[, buffering]]])
Open an encoded file using the given *mode* and return a wrapped version
providing transparent encoding/decoding. The default file mode is ``'r'``
meaning to open the file in read mode.
.. note:: .. note::
The wrapped version's methods will accept and return strings only. Bytes Search function registration is not currently reversible,
arguments will be rejected. which may cause problems in some cases, such as unit testing or
module reloading.
While the builtin :func:`open` and the associated :mod:`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:
.. function:: open(filename, mode='r', encoding=None, errors='strict', buffering=1)
Open an encoded file using the given *mode* and return an instance of
:class:`StreamReaderWriter`, providing transparent encoding/decoding.
The default file mode is ``'r'``, meaning to open the file in read mode.
.. note:: .. note::
Files are always opened in binary mode, even if no binary mode was Underlying encoded files are always opened in binary mode.
specified. This is done to avoid data loss due to encodings using 8-bit No automatic conversion of ``'\n'`` is done on reading and writing.
values. This means that no automatic conversion of ``b'\n'`` is done The *mode* argument may be any binary mode acceptable to the built-in
on reading and writing. :func:`open` function; the ``'b'`` is automatically added.
*encoding* specifies the encoding which is to be used for the file. *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* may be given to define the error handling. It defaults to ``'strict'`` *errors* may be given to define the error handling. It defaults to ``'strict'``
which causes a :exc:`ValueError` to be raised in case an encoding error occurs. which causes a :exc:`ValueError` to be raised in case an encoding error occurs.
@ -266,12 +199,15 @@ utility functions:
.. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict') .. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict')
Return a wrapped version of file which provides transparent encoding Return a :class:`StreamRecoder` instance, a wrapped version of *file*
translation. which provides transparent transcoding. The original file is closed
when the wrapped version is closed.
Bytes written to the wrapped file are interpreted according to the given Data written to the wrapped file is decoded according to the given
*data_encoding* and then written to the original file as bytes using the *data_encoding* and then written to the original file as bytes using
*file_encoding*. *file_encoding*. Bytes read from the original file are decoded
according to *file_encoding*, and the result is encoded
using *data_encoding*.
If *file_encoding* is not given, it defaults to *data_encoding*. If *file_encoding* is not given, it defaults to *data_encoding*.
@ -283,14 +219,16 @@ utility functions:
.. function:: iterencode(iterator, encoding, errors='strict', **kwargs) .. function:: iterencode(iterator, encoding, errors='strict', **kwargs)
Uses an incremental encoder to iteratively encode the input provided by Uses an incremental encoder to iteratively encode the input provided by
*iterator*. This function is a :term:`generator`. *errors* (as well as any *iterator*. This function is a :term:`generator`.
The *errors* argument (as well as any
other keyword argument) is passed through to the incremental encoder. other keyword argument) is passed through to the incremental encoder.
.. function:: iterdecode(iterator, encoding, errors='strict', **kwargs) .. function:: iterdecode(iterator, encoding, errors='strict', **kwargs)
Uses an incremental decoder to iteratively decode the input provided by Uses an incremental decoder to iteratively decode the input provided by
*iterator*. This function is a :term:`generator`. *errors* (as well as any *iterator*. This function is a :term:`generator`.
The *errors* argument (as well as any
other keyword argument) is passed through to the incremental decoder. other keyword argument) is passed through to the incremental decoder.
@ -309,9 +247,10 @@ and writing to platform dependent files:
BOM_UTF32_BE BOM_UTF32_BE
BOM_UTF32_LE BOM_UTF32_LE
These constants define various encodings of the Unicode byte order mark (BOM) These constants define various byte sequences,
used in UTF-16 and UTF-32 data streams to indicate the byte order used in the being Unicode byte order marks (BOMs) for several encodings. They are
stream or file and in UTF-8 as a Unicode signature. :const:`BOM_UTF16` is either used in UTF-16 and UTF-32 data streams to indicate the byte order used,
and in UTF-8 as a Unicode signature. :const:`BOM_UTF16` is either
:const:`BOM_UTF16_BE` or :const:`BOM_UTF16_LE` depending on the platform's :const:`BOM_UTF16_BE` or :const:`BOM_UTF16_LE` depending on the platform's
native byte order, :const:`BOM` is an alias for :const:`BOM_UTF16`, native byte order, :const:`BOM` is an alias for :const:`BOM_UTF16`,
:const:`BOM_LE` for :const:`BOM_UTF16_LE` and :const:`BOM_BE` for :const:`BOM_LE` for :const:`BOM_UTF16_LE` and :const:`BOM_BE` for
@ -325,20 +264,25 @@ Codec Base Classes
------------------ ------------------
The :mod:`codecs` module defines a set of base classes which define the The :mod:`codecs` module defines a set of base classes which define the
interface and can also be used to easily write your own codecs for use in interfaces for working with codec objects, and can also be used as the basis
Python. for custom codec implementations.
Each codec has to define four interfaces to make it usable as codec in Python: 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 stateless encoder, stateless decoder, stream reader and stream writer. The
stream reader and writers typically reuse the stateless encoder/decoder to stream reader and writers typically reuse the stateless encoder/decoder to
implement the file protocols. implement the file protocols. Codec authors also need to define how the
codec will handle encoding and decoding errors.
The :class:`Codec` class defines the interface for stateless encoders/decoders.
To simplify and standardize error handling, the :meth:`~Codec.encode` and .. _error-handlers:
:meth:`~Codec.decode` methods may implement different error handling schemes by
providing the *errors* string argument. The following string values are defined Error Handlers
and implemented by all standard Python codecs: ^^^^^^^^^^^^^^
To simplify and standardize error handling,
codecs may implement different error handling schemes by
accepting the *errors* string argument. The following string values are
defined and implemented by all standard Python codecs:
.. tabularcolumns:: |l|L| .. tabularcolumns:: |l|L|
@ -346,36 +290,52 @@ and implemented by all standard Python codecs:
| Value | Meaning | | Value | Meaning |
+=========================+===============================================+ +=========================+===============================================+
| ``'strict'`` | Raise :exc:`UnicodeError` (or a subclass); | | ``'strict'`` | Raise :exc:`UnicodeError` (or a subclass); |
| | this is the default. | | | this is the default. Implemented in |
| | :func:`strict_errors`. |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
| ``'ignore'`` | Ignore the character and continue with the | | ``'ignore'`` | Ignore the malformed data and continue |
| | next. | | | without further notice. Implemented in |
| | :func:`ignore_errors`. |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
The following error handlers are only applicable to
:term:`text encodings <text encoding>`:
+-------------------------+-----------------------------------------------+
| Value | Meaning |
+=========================+===============================================+
| ``'replace'`` | Replace with a suitable replacement | | ``'replace'`` | Replace with a suitable replacement |
| | character; Python will use the official | | | marker; Python will use the official |
| | U+FFFD REPLACEMENT CHARACTER for the built-in | | | ``U+FFFD`` REPLACEMENT CHARACTER for the |
| | Unicode codecs on decoding and '?' on | | | built-in codecs on decoding, and '?' on |
| | encoding. | | | encoding. Implemented in |
| | :func:`replace_errors`. |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
| ``'xmlcharrefreplace'`` | Replace with the appropriate XML character | | ``'xmlcharrefreplace'`` | Replace with the appropriate XML character |
| | reference (only for encoding). | | | reference (only for encoding). Implemented |
| | in :func:`xmlcharrefreplace_errors`. |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
| ``'backslashreplace'`` | Replace with backslashed escape sequences | | ``'backslashreplace'`` | Replace with backslashed escape sequences |
| | (only for encoding). | | | (only for encoding). Implemented in |
| | :func:`backslashreplace_errors`. |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
| ``'surrogateescape'`` | Replace byte with surrogate U+DCxx, as defined| | ``'surrogateescape'`` | On decoding, replace byte with individual |
| | in :pep:`383`. | | | 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.) |
+-------------------------+-----------------------------------------------+ +-------------------------+-----------------------------------------------+
In addition, the following error handlers are specific to Unicode encoding In addition, the following error handler is specific to the given codecs:
schemes:
+-------------------+------------------------+-------------------------------------------+ +-------------------+------------------------+-------------------------------------------+
| Value | Codec | Meaning | | Value | Codecs | Meaning |
+===================+========================+===========================================+ +===================+========================+===========================================+
|``'surrogatepass'``| utf-8, utf-16, utf-32, | Allow encoding and decoding of surrogate | |``'surrogatepass'``| utf-8, utf-16, utf-32, | Allow encoding and decoding of surrogate |
| | utf-16-be, utf-16-le, | codes in all the Unicode encoding schemes.| | | utf-16-be, utf-16-le, | codes. These codecs normally treat the |
| | utf-32-be, utf-32-le | | | | utf-32-be, utf-32-le | presence of surrogates as an error. |
+-------------------+------------------------+-------------------------------------------+ +-------------------+------------------------+-------------------------------------------+
.. versionadded:: 3.1 .. versionadded:: 3.1
@ -384,26 +344,96 @@ schemes:
.. versionchanged:: 3.4 .. versionchanged:: 3.4
The ``'surrogatepass'`` error handlers now works with utf-16\* and utf-32\* codecs. The ``'surrogatepass'`` error handlers now works with utf-16\* and utf-32\* codecs.
The set of allowed values can be extended via :meth:`register_error`. The set of allowed values can be extended by registering a new named error
handler:
.. function:: register_error(name, error_handler)
Register the error handling function *error_handler* under the name *name*.
The *error_handler* argument will be called during encoding and decoding
in case of an error, when *name* is specified as the errors parameter.
For encoding, *error_handler* will be called with a :exc:`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 :class:`str` or
:class:`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 :exc:`IndexError` will be raised.
Decoding and translating works similarly, except :exc:`UnicodeDecodeError` or
:exc:`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:
.. function:: lookup_error(name)
Return the error handler previously registered under the name *name*.
Raises a :exc:`LookupError` in case the handler cannot be found.
The following standard error handlers are also made available as module level
functions:
.. function:: strict_errors(exception)
Implements the ``'strict'`` error handling: each encoding or
decoding error raises a :exc:`UnicodeError`.
.. function:: replace_errors(exception)
Implements the ``'replace'`` error handling (for :term:`text encodings
<text encoding>` only): substitutes ``'?'`` for encoding errors
(to be encoded by the codec), and ``'\ufffd'`` (the Unicode replacement
character, ``'<27>'``) for decoding errors.
.. function:: ignore_errors(exception)
Implements the ``'ignore'`` error handling: malformed data is ignored and
encoding or decoding is continued without further notice.
.. function:: xmlcharrefreplace_errors(exception)
Implements the ``'xmlcharrefreplace'`` error handling (for encoding with
:term:`text encodings <text encoding>` only): the
unencodable character is replaced by an appropriate XML character reference.
.. function:: backslashreplace_errors(exception)
Implements the ``'backslashreplace'`` error handling (for encoding with
:term:`text encodings <text encoding>` only): the
unencodable character is replaced by a backslashed escape sequence.
.. _codec-objects: .. _codec-objects:
Codec Objects Stateless Encoding and Decoding
^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The :class:`Codec` class defines these methods which also define the function The base :class:`Codec` class defines these methods which also define the
interfaces of the stateless encoder and decoder: function interfaces of the stateless encoder and decoder:
.. method:: Codec.encode(input[, errors]) .. method:: Codec.encode(input[, errors])
Encodes the object *input* and returns a tuple (output object, length consumed). Encodes the object *input* and returns a tuple (output object, length consumed).
Encoding converts a string object to a bytes object using a particular For instance, :term:`text encoding` converts
a string object to a bytes object using a particular
character set encoding (e.g., ``cp1252`` or ``iso-8859-1``). character set encoding (e.g., ``cp1252`` or ``iso-8859-1``).
*errors* defines the error handling to apply. It defaults to ``'strict'`` The *errors* argument defines the error handling to apply.
handling. It defaults to ``'strict'`` handling.
The method may not store state in the :class:`Codec` instance. Use The method may not store state in the :class:`Codec` instance. Use
:class:`StreamCodec` for codecs which have to keep state in order to make :class:`StreamCodec` for codecs which have to keep state in order to make
@ -416,14 +446,16 @@ interfaces of the stateless encoder and decoder:
.. method:: Codec.decode(input[, errors]) .. method:: Codec.decode(input[, errors])
Decodes the object *input* and returns a tuple (output object, length Decodes the object *input* and returns a tuple (output object, length
consumed). Decoding converts a bytes object encoded using a particular consumed). For instance, for a :term:`text encoding`, decoding converts
a bytes object encoded using a particular
character set encoding to a string object. character set encoding to a string object.
*input* must be a bytes object or one which provides the read-only character 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. buffer interface -- for example, buffer objects and memory mapped files.
*errors* defines the error handling to apply. It defaults to ``'strict'`` The *errors* argument defines the error handling to apply.
handling. It defaults to ``'strict'`` handling.
The method may not store state in the :class:`Codec` instance. Use The method may not store state in the :class:`Codec` instance. Use
:class:`StreamCodec` for codecs which have to keep state in order to make :class:`StreamCodec` for codecs which have to keep state in order to make
@ -432,6 +464,10 @@ interfaces of the stateless encoder and decoder:
The decoder must be able to handle zero length input and return an empty object The decoder must be able to handle zero length input and return an empty object
of the output object type in this situation. of the output object type in this situation.
Incremental Encoding and Decoding
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The :class:`IncrementalEncoder` and :class:`IncrementalDecoder` classes provide The :class:`IncrementalEncoder` and :class:`IncrementalDecoder` classes provide
the basic interface for incremental encoding and decoding. Encoding/decoding the 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 input isn't done with one call to the stateless encoder/decoder function, but
@ -449,14 +485,14 @@ encoded/decoded with the stateless encoder/decoder.
.. _incremental-encoder-objects: .. _incremental-encoder-objects:
IncrementalEncoder Objects IncrementalEncoder Objects
^^^^^^^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
The :class:`IncrementalEncoder` class is used for encoding an input in multiple The :class:`IncrementalEncoder` class is used for encoding an input in multiple
steps. It defines the following methods which every incremental encoder must steps. It defines the following methods which every incremental encoder must
define in order to be compatible with the Python codec registry. define in order to be compatible with the Python codec registry.
.. class:: IncrementalEncoder([errors]) .. class:: IncrementalEncoder(errors='strict')
Constructor for an :class:`IncrementalEncoder` instance. Constructor for an :class:`IncrementalEncoder` instance.
@ -465,26 +501,14 @@ define in order to be compatible with the Python codec registry.
the Python codec registry. the Python codec registry.
The :class:`IncrementalEncoder` may implement different error handling schemes The :class:`IncrementalEncoder` may implement different error handling schemes
by providing the *errors* keyword argument. These parameters are predefined: by providing the *errors* keyword argument. See :ref:`error-handlers` for
possible values.
* ``'strict'`` Raise :exc:`ValueError` (or a subclass); this is the default.
* ``'ignore'`` Ignore the character and continue with the next.
* ``'replace'`` Replace with a suitable replacement character
* ``'xmlcharrefreplace'`` Replace with the appropriate XML character reference
* ``'backslashreplace'`` Replace with backslashed escape sequences.
The *errors* argument will be assigned to an attribute of the same name. 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 Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the :class:`IncrementalEncoder` handling strategies during the lifetime of the :class:`IncrementalEncoder`
object. object.
The set of allowed values for the *errors* argument can be extended with
:func:`register_error`.
.. method:: encode(object[, final]) .. method:: encode(object[, final])
@ -496,7 +520,8 @@ define in order to be compatible with the Python codec registry.
.. method:: reset() .. method:: reset()
Reset the encoder to the initial state. The output is discarded: call Reset the encoder to the initial state. The output is discarded: call
``.encode('', final=True)`` to reset the encoder and to get the output. ``.encode(object, final=True)``, passing an empty byte or text string
if necessary, to reset the encoder and to get the output.
.. method:: IncrementalEncoder.getstate() .. method:: IncrementalEncoder.getstate()
@ -517,14 +542,14 @@ define in order to be compatible with the Python codec registry.
.. _incremental-decoder-objects: .. _incremental-decoder-objects:
IncrementalDecoder Objects IncrementalDecoder Objects
^^^^^^^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
The :class:`IncrementalDecoder` class is used for decoding an input in multiple The :class:`IncrementalDecoder` class is used for decoding an input in multiple
steps. It defines the following methods which every incremental decoder must steps. It defines the following methods which every incremental decoder must
define in order to be compatible with the Python codec registry. define in order to be compatible with the Python codec registry.
.. class:: IncrementalDecoder([errors]) .. class:: IncrementalDecoder(errors='strict')
Constructor for an :class:`IncrementalDecoder` instance. Constructor for an :class:`IncrementalDecoder` instance.
@ -533,22 +558,14 @@ define in order to be compatible with the Python codec registry.
the Python codec registry. the Python codec registry.
The :class:`IncrementalDecoder` may implement different error handling schemes The :class:`IncrementalDecoder` may implement different error handling schemes
by providing the *errors* keyword argument. These parameters are predefined: by providing the *errors* keyword argument. See :ref:`error-handlers` for
possible values.
* ``'strict'`` Raise :exc:`ValueError` (or a subclass); this is the default.
* ``'ignore'`` Ignore the character and continue with the next.
* ``'replace'`` Replace with a suitable replacement character.
The *errors* argument will be assigned to an attribute of the same name. 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 Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the :class:`IncrementalDecoder` handling strategies during the lifetime of the :class:`IncrementalDecoder`
object. object.
The set of allowed values for the *errors* argument can be extended with
:func:`register_error`.
.. method:: decode(object[, final]) .. method:: decode(object[, final])
@ -587,6 +604,10 @@ define in order to be compatible with the Python codec registry.
returned by :meth:`getstate`. returned by :meth:`getstate`.
Stream Encoding and Decoding
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The :class:`StreamWriter` and :class:`StreamReader` classes provide generic The :class:`StreamWriter` and :class:`StreamReader` classes provide generic
working interfaces which can be used to implement new encoding submodules very working interfaces which can be used to implement new encoding submodules very
easily. See :mod:`encodings.utf_8` for an example of how this is done. easily. See :mod:`encodings.utf_8` for an example of how this is done.
@ -595,14 +616,14 @@ easily. See :mod:`encodings.utf_8` for an example of how this is done.
.. _stream-writer-objects: .. _stream-writer-objects:
StreamWriter Objects StreamWriter Objects
^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~
The :class:`StreamWriter` class is a subclass of :class:`Codec` and defines the The :class:`StreamWriter` class is a subclass of :class:`Codec` and defines the
following methods which every stream writer must define in order to be following methods which every stream writer must define in order to be
compatible with the Python codec registry. compatible with the Python codec registry.
.. class:: StreamWriter(stream[, errors]) .. class:: StreamWriter(stream, errors='strict')
Constructor for a :class:`StreamWriter` instance. Constructor for a :class:`StreamWriter` instance.
@ -610,29 +631,17 @@ compatible with the Python codec registry.
additional keyword arguments, but only the ones defined here are used by the additional keyword arguments, but only the ones defined here are used by the
Python codec registry. Python codec registry.
*stream* must be a file-like object open for writing binary data. The *stream* argument must be a file-like object open for writing
text or binary data, as appropriate for the specific codec.
The :class:`StreamWriter` may implement different error handling schemes by The :class:`StreamWriter` may implement different error handling schemes by
providing the *errors* keyword argument. These parameters are predefined: providing the *errors* keyword argument. See :ref:`error-handlers` for
the standard error handlers the underlying stream codec may support.
* ``'strict'`` Raise :exc:`ValueError` (or a subclass); this is the default.
* ``'ignore'`` Ignore the character and continue with the next.
* ``'replace'`` Replace with a suitable replacement character
* ``'xmlcharrefreplace'`` Replace with the appropriate XML character reference
* ``'backslashreplace'`` Replace with backslashed escape sequences.
The *errors* argument will be assigned to an attribute of the same name. 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 Assigning to this attribute makes it possible to switch between different error
handling strategies during the lifetime of the :class:`StreamWriter` object. handling strategies during the lifetime of the :class:`StreamWriter` object.
The set of allowed values for the *errors* argument can be extended with
:func:`register_error`.
.. method:: write(object) .. method:: write(object)
Writes the object's contents encoded to the stream. Writes the object's contents encoded to the stream.
@ -641,7 +650,8 @@ compatible with the Python codec registry.
.. method:: writelines(list) .. method:: writelines(list)
Writes the concatenated list of strings to the stream (possibly by reusing Writes the concatenated list of strings to the stream (possibly by reusing
the :meth:`write` method). the :meth:`write` method). The standard bytes-to-bytes codecs
do not support this method.
.. method:: reset() .. method:: reset()
@ -660,14 +670,14 @@ all other methods and attributes from the underlying stream.
.. _stream-reader-objects: .. _stream-reader-objects:
StreamReader Objects StreamReader Objects
^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~
The :class:`StreamReader` class is a subclass of :class:`Codec` and defines the The :class:`StreamReader` class is a subclass of :class:`Codec` and defines the
following methods which every stream reader must define in order to be following methods which every stream reader must define in order to be
compatible with the Python codec registry. compatible with the Python codec registry.
.. class:: StreamReader(stream[, errors]) .. class:: StreamReader(stream, errors='strict')
Constructor for a :class:`StreamReader` instance. Constructor for a :class:`StreamReader` instance.
@ -675,16 +685,12 @@ compatible with the Python codec registry.
additional keyword arguments, but only the ones defined here are used by the additional keyword arguments, but only the ones defined here are used by the
Python codec registry. Python codec registry.
*stream* must be a file-like object open for reading (binary) data. The *stream* argument must be a file-like object open for reading
text or binary data, as appropriate for the specific codec.
The :class:`StreamReader` may implement different error handling schemes by The :class:`StreamReader` may implement different error handling schemes by
providing the *errors* keyword argument. These parameters are defined: providing the *errors* keyword argument. See :ref:`error-handlers` for
the standard error handlers the underlying stream codec may support.
* ``'strict'`` Raise :exc:`ValueError` (or a subclass); this is the default.
* ``'ignore'`` Ignore the character and continue with the next.
* ``'replace'`` Replace with a suitable replacement character.
The *errors* argument will be assigned to an attribute of the same name. 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 Assigning to this attribute makes it possible to switch between different error
@ -698,17 +704,20 @@ compatible with the Python codec registry.
Decodes data from the stream and returns the resulting object. Decodes data from the stream and returns the resulting object.
*chars* indicates the number of characters to read from the The *chars* argument indicates the number of decoded
stream. :func:`read` will never return more than *chars* characters, but code points or bytes to return. The :func:`read` method will
it might return less, if there are not enough characters available. never return more data than requested, but it might return less,
if there is not enough available.
*size* indicates the approximate maximum number of bytes to read from the The *size* argument indicates the approximate maximum
stream for decoding purposes. The decoder can modify this setting as 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 appropriate. The default value -1 indicates to read and decode as much as
possible. *size* is intended to prevent having to decode huge files in possible. This parameter is intended to
one step. prevent having to decode huge files in one step.
*firstline* indicates that it would be sufficient to only return the first The *firstline* flag indicates that
it would be sufficient to only return the first
line, if there are decoding errors on later lines. line, if there are decoding errors on later lines.
The method should use a greedy read strategy meaning that it should read The method should use a greedy read strategy meaning that it should read
@ -751,17 +760,13 @@ compatible with the Python codec registry.
In addition to the above methods, the :class:`StreamReader` must also inherit In addition to the above methods, the :class:`StreamReader` must also inherit
all other methods and attributes from the underlying stream. all other methods and attributes from the underlying stream.
The next two base classes are included for convenience. They are not needed by
the codec registry, but may provide useful in practice.
.. _stream-reader-writer: .. _stream-reader-writer:
StreamReaderWriter Objects StreamReaderWriter Objects
^^^^^^^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
The :class:`StreamReaderWriter` allows wrapping streams which work in both read The :class:`StreamReaderWriter` is a convenience class that allows wrapping
and write modes. streams which work in both read and write modes.
The design is such that one can use the factory functions returned by the The design is such that one can use the factory functions returned by the
:func:`lookup` function to construct the instance. :func:`lookup` function to construct the instance.
@ -782,9 +787,9 @@ methods and attributes from the underlying stream.
.. _stream-recoder-objects: .. _stream-recoder-objects:
StreamRecoder Objects StreamRecoder Objects
^^^^^^^^^^^^^^^^^^^^^ ~~~~~~~~~~~~~~~~~~~~~
The :class:`StreamRecoder` provide a frontend - backend view of encoding data The :class:`StreamRecoder` translates data from one encoding to another,
which is sometimes useful when dealing with different encoding environments. which is sometimes useful when dealing with different encoding environments.
The design is such that one can use the factory functions returned by the The design is such that one can use the factory functions returned by the
@ -794,22 +799,20 @@ The design is such that one can use the factory functions returned by the
.. class:: StreamRecoder(stream, encode, decode, Reader, Writer, errors) .. class:: StreamRecoder(stream, encode, decode, Reader, Writer, errors)
Creates a :class:`StreamRecoder` instance which implements a two-way conversion: Creates a :class:`StreamRecoder` instance which implements a two-way conversion:
*encode* and *decode* work on the frontend (the input to :meth:`read` and output *encode* and *decode* work on the frontend — the data visible to
of :meth:`write`) while *Reader* and *Writer* work on the backend (reading and code calling :meth:`read` and :meth:`write`, while *Reader* and *Writer*
writing to the stream). work on the backend — the data in *stream*.
You can use these objects to do transparent direct recodings from e.g. Latin-1 You can use these objects to do transparent transcodings from e.g. Latin-1
to UTF-8 and back. to UTF-8 and back.
*stream* must be a file-like object. The *stream* argument must be a file-like object.
*encode*, *decode* must adhere to the :class:`Codec` interface. *Reader*, The *encode* and *decode* arguments must
adhere to the :class:`Codec` interface. *Reader* and
*Writer* must be factory functions or classes providing objects of the *Writer* must be factory functions or classes providing objects of the
:class:`StreamReader` and :class:`StreamWriter` interface respectively. :class:`StreamReader` and :class:`StreamWriter` interface respectively.
*encode* and *decode* are needed for the frontend translation, *Reader* and
*Writer* for the backend translation.
Error handling is done in the same way as defined for the stream readers and Error handling is done in the same way as defined for the stream readers and
writers. writers.
@ -824,20 +827,23 @@ methods and attributes from the underlying stream.
Encodings and Unicode Encodings and Unicode
--------------------- ---------------------
Strings are stored internally as sequences of codepoints in range ``0 - 10FFFF`` Strings are stored internally as sequences of codepoints in
(see :pep:`393` for more details about the implementation). range ``0x0``-``0x10FFFF``. (See :pep:`393` for
Once a string object is used outside of CPU and memory, CPU endianness more details about the implementation.)
and how these arrays are stored as bytes become an issue. Transforming a Once a string object is used outside of CPU and memory, endianness
string object into a sequence of bytes is called encoding and recreating the and how these arrays are stored as bytes become an issue. As with other
string object from the sequence of bytes is known as decoding. There are many codecs, serialising a string into a sequence of bytes is known as *encoding*,
different methods for how this transformation can be done (these methods are and recreating the string from the sequence of bytes is known as *decoding*.
also called encodings). The simplest method is to map the codepoints 0-255 to There are a variety of different text serialisation codecs, which are
the bytes ``0x0``-``0xff``. This means that a string object that contains collectivity referred to as :term:`text encodings <text encoding>`.
codepoints above ``U+00FF`` can't be encoded with this method (which is called
``'latin-1'`` or ``'iso-8859-1'``). :func:`str.encode` will raise a The simplest text encoding (called ``'latin-1'`` or ``'iso-8859-1'``) maps
:exc:`UnicodeEncodeError` that looks like this: ``UnicodeEncodeError: 'latin-1' the codepoints 0-255 to the bytes ``0x0``-``0xff``, which means that a string
codec can't encode character '\u1234' in position 3: ordinal not in object that contains codepoints above ``U+00FF`` can't be encoded with this
range(256)``. codec. Doing so will raise a :exc:`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 There's another group of encodings (the so called charmap encodings) that choose
a different subset of all Unicode code points and how these codepoints are a different subset of all Unicode code points and how these codepoints are
@ -1184,7 +1190,8 @@ particular, the following variants typically exist:
.. versionchanged:: 3.4 .. versionchanged:: 3.4
The utf-16\* and utf-32\* encoders no longer allow surrogate code points 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 (``U+D800``--``U+DFFF``) to be encoded.
The utf-32\* decoders no longer decode
byte sequences that correspond to surrogate code points. byte sequences that correspond to surrogate code points.
@ -1212,7 +1219,9 @@ encodings.
+====================+=========+===========================+ +====================+=========+===========================+
| idna | | Implements :rfc:`3490`, | | idna | | Implements :rfc:`3490`, |
| | | see also | | | | see also |
| | | :mod:`encodings.idna` | | | | :mod:`encodings.idna`. |
| | | Only ``errors='strict'`` |
| | | is supported. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| mbcs | dbcs | Windows only: Encode | | mbcs | dbcs | Windows only: Encode |
| | | operand according to the | | | | operand according to the |
@ -1220,31 +1229,44 @@ encodings.
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| palmos | | Encoding of PalmOS 3.5 | | palmos | | Encoding of PalmOS 3.5 |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| punycode | | Implements :rfc:`3492` | | punycode | | Implements :rfc:`3492`. |
| | | Stateful codecs are not |
| | | supported. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| raw_unicode_escape | | Produce a string that is | | raw_unicode_escape | | Latin-1 encoding with |
| | | suitable as raw Unicode | | | | ``\uXXXX`` and |
| | | literal in Python source | | | | ``\UXXXXXXXX`` for other |
| | | code | | | | code points. Existing |
| | | backslashes are not |
| | | escaped in any way. |
| | | It is used in the Python |
| | | pickle protocol. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| undefined | | Raise an exception for | | undefined | | Raise an exception for |
| | | all conversions. Can be | | | | all conversions, even |
| | | used as the system | | | | empty strings. The error |
| | | encoding if no automatic | | | | handler is ignored. |
| | | coercion between byte and |
| | | Unicode strings is |
| | | desired. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| unicode_escape | | Produce a string that is | | unicode_escape | | Encoding suitable as the |
| | | suitable as Unicode | | | | contents of a Unicode |
| | | literal in Python source | | | | literal in ASCII-encoded |
| | | code | | | | Python source code, |
| | | except that quotes are |
| | | not escaped. Decodes from |
| | | Latin-1 source code. |
| | | Beware that Python source |
| | | code actually uses UTF-8 |
| | | by default. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
| unicode_internal | | Return the internal | | unicode_internal | | Return the internal |
| | | representation of the | | | | representation of the |
| | | operand | | | | operand. Stateful codecs |
| | | are not supported. |
| | | | | | | |
| | | .. deprecated:: 3.3 | | | | .. deprecated:: 3.3 |
| | | This representation is |
| | | obsoleted by |
| | | :pep:`393`. |
+--------------------+---------+---------------------------+ +--------------------+---------+---------------------------+
.. _binary-transforms: .. _binary-transforms:
@ -1253,7 +1275,8 @@ Binary Transforms
^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^
The following codecs provide binary transforms: :term:`bytes-like object` The following codecs provide binary transforms: :term:`bytes-like object`
to :class:`bytes` mappings. to :class:`bytes` mappings. They are not supported by :meth:`bytes.decode`
(which only produces :class:`str` output).
.. tabularcolumns:: |l|L|L|L| .. tabularcolumns:: |l|L|L|L|
@ -1308,7 +1331,8 @@ Text Transforms
^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^
The following codec provides a text transform: a :class:`str` to :class:`str` The following codec provides a text transform: a :class:`str` to :class:`str`
mapping. mapping. It is not supported by :meth:`str.encode` (which only produces
:class:`bytes` output).
.. tabularcolumns:: |l|l|L| .. tabularcolumns:: |l|l|L|

8
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@ -939,15 +939,17 @@ are always available. They are listed here in alphabetical order.
*encoding* is the name of the encoding used to decode or encode the file. *encoding* is the name of the encoding used to decode or encode the file.
This should only be used in text mode. The default encoding is platform This should only be used in text mode. The default encoding is platform
dependent (whatever :func:`locale.getpreferredencoding` returns), but any dependent (whatever :func:`locale.getpreferredencoding` returns), but any
encoding supported by Python can be used. See the :mod:`codecs` module for :term:`text encoding` supported by Python
can be used. See the :mod:`codecs` module for
the list of supported encodings. the list of supported encodings.
*errors* is an optional string that specifies how encoding and decoding *errors* is an optional string that specifies how encoding and decoding
errors are to be handled--this cannot be used in binary mode. errors are to be handled--this cannot be used in binary mode.
A variety of standard error handlers are available, though any A variety of standard error handlers are available
(listed under :ref:`error-handlers`), though any
error handling name that has been registered with error handling name that has been registered with
:func:`codecs.register_error` is also valid. The standard names :func:`codecs.register_error` is also valid. The standard names
are: include:
* ``'strict'`` to raise a :exc:`ValueError` exception if there is * ``'strict'`` to raise a :exc:`ValueError` exception if there is
an encoding error. The default value of ``None`` has the same an encoding error. The default value of ``None`` has the same

4
Doc/library/stdtypes.rst
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@ -1512,7 +1512,7 @@ expression support in the :mod:`re` module).
a :exc:`UnicodeError`. Other possible a :exc:`UnicodeError`. Other possible
values are ``'ignore'``, ``'replace'``, ``'xmlcharrefreplace'``, values are ``'ignore'``, ``'replace'``, ``'xmlcharrefreplace'``,
``'backslashreplace'`` and any other name registered via ``'backslashreplace'`` and any other name registered via
:func:`codecs.register_error`, see section :ref:`codec-base-classes`. For a :func:`codecs.register_error`, see section :ref:`error-handlers`. For a
list of possible encodings, see section :ref:`standard-encodings`. list of possible encodings, see section :ref:`standard-encodings`.
.. versionchanged:: 3.1 .. versionchanged:: 3.1
@ -2384,7 +2384,7 @@ arbitrary binary data.
error handling scheme. The default for *errors* is ``'strict'``, meaning error handling scheme. The default for *errors* is ``'strict'``, meaning
that encoding errors raise a :exc:`UnicodeError`. Other possible values are that encoding errors raise a :exc:`UnicodeError`. Other possible values are
``'ignore'``, ``'replace'`` and any other name registered via ``'ignore'``, ``'replace'`` and any other name registered via
:func:`codecs.register_error`, see section :ref:`codec-base-classes`. For a :func:`codecs.register_error`, see section :ref:`error-handlers`. For a
list of possible encodings, see section :ref:`standard-encodings`. list of possible encodings, see section :ref:`standard-encodings`.
.. note:: .. note::

2
Doc/library/tarfile.rst
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@ -794,7 +794,7 @@ metadata must be either decoded or encoded. If *encoding* is not set
appropriately, this conversion may fail. appropriately, this conversion may fail.
The *errors* argument defines how characters are treated that cannot be The *errors* argument defines how characters are treated that cannot be
converted. Possible values are listed in section :ref:`codec-base-classes`. converted. Possible values are listed in section :ref:`error-handlers`.
The default scheme is ``'surrogateescape'`` which Python also uses for its The default scheme is ``'surrogateescape'`` which Python also uses for its
file system calls, see :ref:`os-filenames`. file system calls, see :ref:`os-filenames`.

71
Lib/codecs.py
View File

@ -346,8 +346,7 @@ class StreamWriter(Codec):
""" Creates a StreamWriter instance. """ Creates a StreamWriter instance.
stream must be a file-like object open for writing stream must be a file-like object open for writing.
(binary) data.
The StreamWriter may use different error handling The StreamWriter may use different error handling
schemes by providing the errors keyword argument. These schemes by providing the errors keyword argument. These
@ -421,8 +420,7 @@ class StreamReader(Codec):
""" Creates a StreamReader instance. """ Creates a StreamReader instance.
stream must be a file-like object open for reading stream must be a file-like object open for reading.
(binary) data.
The StreamReader may use different error handling The StreamReader may use different error handling
schemes by providing the errors keyword argument. These schemes by providing the errors keyword argument. These
@ -450,13 +448,12 @@ class StreamReader(Codec):
""" Decodes data from the stream self.stream and returns the """ Decodes data from the stream self.stream and returns the
resulting object. resulting object.
chars indicates the number of characters to read from the chars indicates the number of decoded code points or bytes to
stream. read() will never return more than chars return. read() will never return more data than requested,
characters, but it might return less, if there are not enough but it might return less, if there is not enough available.
characters available.
size indicates the approximate maximum number of bytes to size indicates the approximate maximum number of decoded
read from the stream for decoding purposes. The decoder bytes or code points to read for decoding. The decoder
can modify this setting as appropriate. The default value can modify this setting as appropriate. The default value
-1 indicates to read and decode as much as possible. size -1 indicates to read and decode as much as possible. size
is intended to prevent having to decode huge files in one is intended to prevent having to decode huge files in one
@ -467,7 +464,7 @@ class StreamReader(Codec):
will be returned, the rest of the input will be kept until the will be returned, the rest of the input will be kept until the
next call to read(). next call to read().
The method should use a greedy read strategy meaning that The method should use a greedy read strategy, meaning that
it should read as much data as is allowed within the it should read as much data as is allowed within the
definition of the encoding and the given size, e.g. if definition of the encoding and the given size, e.g. if
optional encoding endings or state markers are available optional encoding endings or state markers are available
@ -602,7 +599,7 @@ class StreamReader(Codec):
def readlines(self, sizehint=None, keepends=True): def readlines(self, sizehint=None, keepends=True):
""" Read all lines available on the input stream """ Read all lines available on the input stream
and return them as list of lines. and return them as a list.
Line breaks are implemented using the codec's decoder Line breaks are implemented using the codec's decoder
method and are included in the list entries. method and are included in the list entries.
@ -750,19 +747,18 @@ class StreamReaderWriter:
class StreamRecoder: class StreamRecoder:
""" StreamRecoder instances provide a frontend - backend """ StreamRecoder instances translate data from one encoding to another.
view of encoding data.
They use the complete set of APIs returned by the They use the complete set of APIs returned by the
codecs.lookup() function to implement their task. codecs.lookup() function to implement their task.
Data written to the stream is first decoded into an Data written to the StreamRecoder is first decoded into an
intermediate format (which is dependent on the given codec intermediate format (depending on the "decode" codec) and then
combination) and then written to the stream using an instance written to the underlying stream using an instance of the provided
of the provided Writer class. Writer class.
In the other direction, data is read from the stream using a In the other direction, data is read from the underlying stream using
Reader instance and then return encoded data to the caller. a Reader instance and then encoded and returned to the caller.
""" """
# Optional attributes set by the file wrappers below # Optional attributes set by the file wrappers below
@ -774,22 +770,17 @@ class StreamRecoder:
""" Creates a StreamRecoder instance which implements a two-way """ Creates a StreamRecoder instance which implements a two-way
conversion: encode and decode work on the frontend (the conversion: encode and decode work on the frontend (the
input to .read() and output of .write()) while data visible to .read() and .write()) while Reader and Writer
Reader and Writer work on the backend (reading and work on the backend (the data in stream).
writing to the stream).
You can use these objects to do transparent direct You can use these objects to do transparent
recodings from e.g. latin-1 to utf-8 and back. transcodings from e.g. latin-1 to utf-8 and back.
stream must be a file-like object. stream must be a file-like object.
encode, decode must adhere to the Codec interface, Reader, encode and decode must adhere to the Codec interface; Reader and
Writer must be factory functions or classes providing the Writer must be factory functions or classes providing the
StreamReader, StreamWriter interface resp. StreamReader and StreamWriter interfaces resp.
encode and decode are needed for the frontend translation,
Reader and Writer for the backend translation. Unicode is
used as intermediate encoding.
Error handling is done in the same way as defined for the Error handling is done in the same way as defined for the
StreamWriter/Readers. StreamWriter/Readers.
@ -864,7 +855,7 @@ class StreamRecoder:
### Shortcuts ### Shortcuts
def open(filename, mode='rb', encoding=None, errors='strict', buffering=1): def open(filename, mode='r', encoding=None, errors='strict', buffering=1):
""" Open an encoded file using the given mode and return """ Open an encoded file using the given mode and return
a wrapped version providing transparent encoding/decoding. a wrapped version providing transparent encoding/decoding.
@ -874,10 +865,8 @@ def open(filename, mode='rb', encoding=None, errors='strict', buffering=1):
codecs. Output is also codec dependent and will usually be codecs. Output is also codec dependent and will usually be
Unicode as well. Unicode as well.
Files are always opened in binary mode, even if no binary mode Underlying encoded files are always opened in binary mode.
was specified. This is done to avoid data loss due to encodings The default file mode is 'r', meaning to open the file in read mode.
using 8-bit values. The default file mode is 'rb' meaning to
open the file in binary read mode.
encoding specifies the encoding which is to be used for the encoding specifies the encoding which is to be used for the
file. file.
@ -913,13 +902,13 @@ def EncodedFile(file, data_encoding, file_encoding=None, errors='strict'):
""" Return a wrapped version of file which provides transparent """ Return a wrapped version of file which provides transparent
encoding translation. encoding translation.
Strings written to the wrapped file are interpreted according Data written to the wrapped file is decoded according
to the given data_encoding and then written to the original to the given data_encoding and then encoded to the underlying
file as string using file_encoding. The intermediate encoding file using file_encoding. The intermediate data type
will usually be Unicode but depends on the specified codecs. will usually be Unicode but depends on the specified codecs.
Strings are read from the file using file_encoding and then Bytes read from the file are decoded using file_encoding and then
passed back to the caller as string using data_encoding. passed back to the caller encoded using data_encoding.
If file_encoding is not given, it defaults to data_encoding. If file_encoding is not given, it defaults to data_encoding.

46
Lib/test/test_codecs.py
View File

@ -1139,6 +1139,8 @@ class RecodingTest(unittest.TestCase):
# Python used to crash on this at exit because of a refcount # Python used to crash on this at exit because of a refcount
# bug in _codecsmodule.c # bug in _codecsmodule.c
self.assertTrue(f.closed)
# From RFC 3492 # From RFC 3492
punycode_testcases = [ punycode_testcases = [
# A Arabic (Egyptian): # A Arabic (Egyptian):
@ -1591,6 +1593,16 @@ class IDNACodecTest(unittest.TestCase):
self.assertEqual(encoder.encode("ample.org."), b"xn--xample-9ta.org.") self.assertEqual(encoder.encode("ample.org."), b"xn--xample-9ta.org.")
self.assertEqual(encoder.encode("", True), b"") self.assertEqual(encoder.encode("", True), b"")
def test_errors(self):
"""Only supports "strict" error handler"""
"python.org".encode("idna", "strict")
b"python.org".decode("idna", "strict")
for errors in ("ignore", "replace", "backslashreplace",
"surrogateescape"):
self.assertRaises(Exception, "python.org".encode, "idna", errors)
self.assertRaises(Exception,
b"python.org".decode, "idna", errors)
class CodecsModuleTest(unittest.TestCase): class CodecsModuleTest(unittest.TestCase):
def test_decode(self): def test_decode(self):
@ -1668,6 +1680,24 @@ class CodecsModuleTest(unittest.TestCase):
for api in codecs.__all__: for api in codecs.__all__:
getattr(codecs, api) getattr(codecs, api)
def test_open(self):
self.addCleanup(support.unlink, support.TESTFN)
for mode in ('w', 'r', 'r+', 'w+', 'a', 'a+'):
with self.subTest(mode), \
codecs.open(support.TESTFN, mode, 'ascii') as file:
self.assertIsInstance(file, codecs.StreamReaderWriter)
def test_undefined(self):
self.assertRaises(UnicodeError, codecs.encode, 'abc', 'undefined')
self.assertRaises(UnicodeError, codecs.decode, b'abc', 'undefined')
self.assertRaises(UnicodeError, codecs.encode, '', 'undefined')
self.assertRaises(UnicodeError, codecs.decode, b'', 'undefined')
for errors in ('strict', 'ignore', 'replace', 'backslashreplace'):
self.assertRaises(UnicodeError,
codecs.encode, 'abc', 'undefined', errors)
self.assertRaises(UnicodeError,
codecs.decode, b'abc', 'undefined', errors)
class StreamReaderTest(unittest.TestCase): class StreamReaderTest(unittest.TestCase):
def setUp(self): def setUp(self):
@ -1801,13 +1831,10 @@ if hasattr(codecs, "mbcs_encode"):
# "undefined" # "undefined"
# The following encodings don't work in stateful mode # The following encodings don't work in stateful mode
broken_unicode_with_streams = [ broken_unicode_with_stateful = [
"punycode", "punycode",
"unicode_internal" "unicode_internal"
] ]
broken_incremental_coders = broken_unicode_with_streams + [
"idna",
]
class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling): class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
def test_basics(self): def test_basics(self):
@ -1827,7 +1854,7 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
(chars, size) = codecs.getdecoder(encoding)(b) (chars, size) = codecs.getdecoder(encoding)(b)
self.assertEqual(chars, s, "encoding=%r" % encoding) self.assertEqual(chars, s, "encoding=%r" % encoding)
if encoding not in broken_unicode_with_streams: if encoding not in broken_unicode_with_stateful:
# check stream reader/writer # check stream reader/writer
q = Queue(b"") q = Queue(b"")
writer = codecs.getwriter(encoding)(q) writer = codecs.getwriter(encoding)(q)
@ -1845,7 +1872,7 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
decodedresult += reader.read() decodedresult += reader.read()
self.assertEqual(decodedresult, s, "encoding=%r" % encoding) self.assertEqual(decodedresult, s, "encoding=%r" % encoding)
if encoding not in broken_incremental_coders: if encoding not in broken_unicode_with_stateful:
# check incremental decoder/encoder and iterencode()/iterdecode() # check incremental decoder/encoder and iterencode()/iterdecode()
try: try:
encoder = codecs.getincrementalencoder(encoding)() encoder = codecs.getincrementalencoder(encoding)()
@ -1894,7 +1921,7 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
from _testcapi import codec_incrementalencoder, codec_incrementaldecoder from _testcapi import codec_incrementalencoder, codec_incrementaldecoder
s = "abc123" # all codecs should be able to encode these s = "abc123" # all codecs should be able to encode these
for encoding in all_unicode_encodings: for encoding in all_unicode_encodings:
if encoding not in broken_incremental_coders: if encoding not in broken_unicode_with_stateful:
# check incremental decoder/encoder (fetched via the C API) # check incremental decoder/encoder (fetched via the C API)
try: try:
cencoder = codec_incrementalencoder(encoding) cencoder = codec_incrementalencoder(encoding)
@ -1934,7 +1961,7 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
for encoding in all_unicode_encodings: for encoding in all_unicode_encodings:
if encoding == "idna": # FIXME: See SF bug #1163178 if encoding == "idna": # FIXME: See SF bug #1163178
continue continue
if encoding in broken_unicode_with_streams: if encoding in broken_unicode_with_stateful:
continue continue
reader = codecs.getreader(encoding)(io.BytesIO(s.encode(encoding))) reader = codecs.getreader(encoding)(io.BytesIO(s.encode(encoding)))
for t in range(5): for t in range(5):
@ -1967,7 +1994,7 @@ class BasicUnicodeTest(unittest.TestCase, MixInCheckStateHandling):
# Check that getstate() and setstate() handle the state properly # Check that getstate() and setstate() handle the state properly
u = "abc123" u = "abc123"
for encoding in all_unicode_encodings: for encoding in all_unicode_encodings:
if encoding not in broken_incremental_coders: if encoding not in broken_unicode_with_stateful:
self.check_state_handling_decode(encoding, u, u.encode(encoding)) self.check_state_handling_decode(encoding, u, u.encode(encoding))
self.check_state_handling_encode(encoding, u, u.encode(encoding)) self.check_state_handling_encode(encoding, u, u.encode(encoding))
@ -2171,6 +2198,7 @@ class WithStmtTest(unittest.TestCase):
f = io.BytesIO(b"\xc3\xbc") f = io.BytesIO(b"\xc3\xbc")
with codecs.EncodedFile(f, "latin-1", "utf-8") as ef: with codecs.EncodedFile(f, "latin-1", "utf-8") as ef:
self.assertEqual(ef.read(), b"\xfc") self.assertEqual(ef.read(), b"\xfc")
self.assertTrue(f.closed)
def test_streamreaderwriter(self): def test_streamreaderwriter(self):
f = io.BytesIO(b"\xc3\xbc") f = io.BytesIO(b"\xc3\xbc")

8
Misc/NEWS
View File

@ -265,6 +265,10 @@ IDLE
Tests Tests
----- -----
- Issue #19548: Added some additional checks to test_codecs to ensure that
statements in the updated documentation remain accurate. Patch by Martin
Panter.
- Issue #22838: All test_re tests now work with unittest test discovery. - Issue #22838: All test_re tests now work with unittest test discovery.
- Issue #22173: Update lib2to3 tests to use unittest test discovery. - Issue #22173: Update lib2to3 tests to use unittest test discovery.
@ -297,6 +301,10 @@ Build
Documentation Documentation
------------- -------------
- Issue #19548: Update the codecs module documentation to better cover the
distinction between text encodings and other codecs, together with other
clarifications. Patch by Martin Panter.
- Issue #22914: Update the Python 2/3 porting HOWTO to describe a more automated - Issue #22914: Update the Python 2/3 porting HOWTO to describe a more automated
approach. approach.

6
Modules/_codecsmodule.c
View File

@ -54,9 +54,9 @@ PyDoc_STRVAR(register__doc__,
"register(search_function)\n\ "register(search_function)\n\
\n\ \n\
Register a codec search function. Search functions are expected to take\n\ Register a codec search function. Search functions are expected to take\n\
one argument, the encoding name in all lower case letters, and return\n\ one argument, the encoding name in all lower case letters, and either\n\
a tuple of functions (encoder, decoder, stream_reader, stream_writer)\n\ return None, or a tuple of functions (encoder, decoder, stream_reader,\n\
(or a CodecInfo object)."); stream_writer) (or a CodecInfo object).");
static static
PyObject *codec_register(PyObject *self, PyObject *search_function) PyObject *codec_register(PyObject *self, PyObject *search_function)