| :mod:`codecs` --- Codec registry and base classes |
| ================================================= |
| |
| .. module:: codecs |
| :synopsis: Encode and decode data and streams. |
| .. moduleauthor:: Marc-André Lemburg <mal@lemburg.com> |
| .. sectionauthor:: Marc-André Lemburg <mal@lemburg.com> |
| .. sectionauthor:: Martin v. Löwis <martin@v.loewis.de> |
| |
| |
| .. index:: |
| single: Unicode |
| single: Codecs |
| pair: Codecs; encode |
| pair: Codecs; decode |
| single: streams |
| pair: stackable; streams |
| |
| This module defines base classes for standard Python codecs (encoders and |
| decoders) and provides access to the internal Python codec registry which |
| manages the codec and error handling lookup process. |
| |
| It defines the following functions: |
| |
| |
| .. function:: register(search_function) |
| |
| 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:`encode`/:meth:`decode` methods of Codec instances (see |
| Codec Interface). 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:`StreamWriter` and :class:`StreamReader`, 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) |
| |
| Looks up the codec info in the Python codec registry and returns a |
| :class:`CodecInfo` object as defined above. |
| |
| 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 |
| found, a :exc:`LookupError` is raised. Otherwise, the :class:`CodecInfo` object |
| is stored in the cache and returned to the caller. |
| |
| To simplify access to the various codecs, the module provides these additional |
| functions which use :func:`lookup` for the codec lookup: |
| |
| |
| .. function:: getencoder(encoding) |
| |
| Look up the codec for the given encoding and return its encoder function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found. |
| |
| |
| .. function:: getdecoder(encoding) |
| |
| Look up the codec for the given encoding and return its decoder function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found. |
| |
| |
| .. function:: getincrementalencoder(encoding) |
| |
| Look up the codec for the given encoding and return its incremental encoder |
| class or factory function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found or the codec |
| doesn't support an incremental encoder. |
| |
| |
| .. function:: getincrementaldecoder(encoding) |
| |
| Look up the codec for the given encoding and return its incremental decoder |
| class or factory function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found or the codec |
| doesn't support an incremental decoder. |
| |
| |
| .. function:: getreader(encoding) |
| |
| Look up the codec for the given encoding and return its StreamReader class or |
| factory function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found. |
| |
| |
| .. function:: getwriter(encoding) |
| |
| Look up the codec for the given encoding and return its StreamWriter class or |
| factory function. |
| |
| Raises a :exc:`LookupError` in case the encoding cannot be found. |
| |
| |
| .. function:: register_error(name, error_handler) |
| |
| Register the error handling function *error_handler* under the name *name*. |
| *error_handler* 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 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:: |
| |
| The wrapped version's methods will accept and return strings only. Bytes |
| arguments will be rejected. |
| |
| .. note:: |
| |
| Files are always opened in binary mode, even if no binary mode was |
| specified. This is done to avoid data loss due to encodings using 8-bit |
| values. This means that no automatic conversion of ``b'\n'`` is done |
| on reading and writing. |
| |
| *encoding* specifies the encoding which is to be used for the file. |
| |
| *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. |
| |
| *buffering* has the same meaning as for the built-in :func:`open` function. It |
| defaults to line buffered. |
| |
| |
| .. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict') |
| |
| Return a wrapped version of file which provides transparent encoding |
| translation. |
| |
| Bytes written to the wrapped file are interpreted according to the given |
| *data_encoding* and then written to the original file as bytes using the |
| *file_encoding*. |
| |
| If *file_encoding* is not given, it defaults to *data_encoding*. |
| |
| *errors* may be given to define the error handling. It defaults to |
| ``'strict'``, which causes :exc:`ValueError` to be raised in case an encoding |
| error occurs. |
| |
| |
| .. function:: iterencode(iterator, encoding, errors='strict', **kwargs) |
| |
| Uses an incremental encoder to iteratively encode the input provided by |
| *iterator*. This function is a :term:`generator`. *errors* (as well as any |
| other keyword argument) is passed through to the incremental encoder. |
| |
| |
| .. function:: iterdecode(iterator, encoding, errors='strict', **kwargs) |
| |
| Uses an incremental decoder to iteratively decode the input provided by |
| *iterator*. This function is a :term:`generator`. *errors* (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: |
| |
| |
| .. data:: BOM |
| BOM_BE |
| BOM_LE |
| BOM_UTF8 |
| BOM_UTF16 |
| BOM_UTF16_BE |
| BOM_UTF16_LE |
| BOM_UTF32 |
| BOM_UTF32_BE |
| BOM_UTF32_LE |
| |
| These constants define various encodings of the Unicode byte order mark (BOM) |
| used in UTF-16 and UTF-32 data streams to indicate the byte order used in the |
| stream or file 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 |
| 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_UTF16_BE`. The others represent the BOM in UTF-8 and UTF-32 |
| encodings. |
| |
| |
| .. _codec-base-classes: |
| |
| Codec Base Classes |
| ------------------ |
| |
| 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 |
| 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 |
| stream reader and writers typically reuse the stateless encoder/decoder to |
| implement the file protocols. |
| |
| The :class:`Codec` class defines the interface for stateless encoders/decoders. |
| |
| To simplify and standardize error handling, the :meth:`encode` and |
| :meth:`decode` methods may implement different error handling schemes by |
| providing the *errors* string argument. The following string values are defined |
| and implemented by all standard Python codecs: |
| |
| .. tabularcolumns:: |l|L| |
| |
| +-------------------------+-----------------------------------------------+ |
| | Value | Meaning | |
| +=========================+===============================================+ |
| | ``'strict'`` | Raise :exc:`UnicodeError` (or a subclass); | |
| | | this is the default. | |
| +-------------------------+-----------------------------------------------+ |
| | ``'ignore'`` | Ignore the character and continue with the | |
| | | next. | |
| +-------------------------+-----------------------------------------------+ |
| | ``'replace'`` | Replace with a suitable replacement | |
| | | character; Python will use the official | |
| | | U+FFFD REPLACEMENT CHARACTER for the built-in | |
| | | Unicode codecs on decoding and '?' on | |
| | | encoding. | |
| +-------------------------+-----------------------------------------------+ |
| | ``'xmlcharrefreplace'`` | Replace with the appropriate XML character | |
| | | reference (only for encoding). | |
| +-------------------------+-----------------------------------------------+ |
| | ``'backslashreplace'`` | Replace with backslashed escape sequences | |
| | | (only for encoding). | |
| +-------------------------+-----------------------------------------------+ |
| | ``'surrogateescape'`` | Replace byte with surrogate U+DCxx, as defined| |
| | | in :pep:`383`. | |
| +-------------------------+-----------------------------------------------+ |
| |
| In addition, the following error handlers are specific to a single codec: |
| |
| +-------------------+---------+-------------------------------------------+ |
| | Value | Codec | Meaning | |
| +===================+=========+===========================================+ |
| |``'surrogatepass'``| utf-8 | Allow encoding and decoding of surrogate | |
| | | | codes in UTF-8. | |
| +-------------------+---------+-------------------------------------------+ |
| |
| .. versionadded:: 3.1 |
| The ``'surrogateescape'`` and ``'surrogatepass'`` error handlers. |
| |
| The set of allowed values can be extended via :meth:`register_error`. |
| |
| |
| .. _codec-objects: |
| |
| Codec Objects |
| ^^^^^^^^^^^^^ |
| |
| The :class:`Codec` class defines these methods which also define the function |
| interfaces of the stateless encoder and decoder: |
| |
| |
| .. method:: Codec.encode(input[, errors]) |
| |
| Encodes the object *input* and returns a tuple (output object, length consumed). |
| Encoding converts a string object to a bytes object using a particular |
| character set encoding (e.g., ``cp1252`` or ``iso-8859-1``). |
| |
| *errors* defines the error handling to apply. It defaults to ``'strict'`` |
| handling. |
| |
| 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 |
| encoding/decoding efficient. |
| |
| The encoder must be able to handle zero length input and return an empty object |
| of the output object type in this situation. |
| |
| |
| .. method:: Codec.decode(input[, errors]) |
| |
| Decodes the object *input* and returns a tuple (output object, length |
| consumed). Decoding converts a bytes object encoded using a particular |
| character set encoding to a string object. |
| |
| *input* must be a bytes object or one which provides the read-only character |
| buffer interface -- for example, buffer objects and memory mapped files. |
| |
| *errors* defines the error handling to apply. It defaults to ``'strict'`` |
| handling. |
| |
| 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 |
| encoding/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 :class:`IncrementalEncoder` and :class:`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 :meth:`encode`/:meth:`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 :meth:`encode`/:meth:`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. |
| |
| |
| .. _incremental-encoder-objects: |
| |
| IncrementalEncoder Objects |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The :class:`IncrementalEncoder` class is used for encoding an input in multiple |
| steps. It defines the following methods which every incremental encoder must |
| define in order to be compatible with the Python codec registry. |
| |
| |
| .. class:: IncrementalEncoder([errors]) |
| |
| Constructor for an :class:`IncrementalEncoder` instance. |
| |
| 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 :class:`IncrementalEncoder` may implement different error handling schemes |
| by providing the *errors* keyword argument. These parameters are predefined: |
| |
| * ``'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. |
| Assigning to this attribute makes it possible to switch between different error |
| handling strategies during the lifetime of the :class:`IncrementalEncoder` |
| object. |
| |
| The set of allowed values for the *errors* argument can be extended with |
| :func:`register_error`. |
| |
| |
| .. method:: encode(object[, final]) |
| |
| Encodes *object* (taking the current state of the encoder into account) |
| and returns the resulting encoded object. If this is the last call to |
| :meth:`encode` *final* must be true (the default is false). |
| |
| |
| .. method:: reset() |
| |
| Reset the encoder to the initial state. The output is discarded: call |
| ``.encode('', final=True)`` to reset the encoder and to get the output. |
| |
| |
| .. method:: 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). |
| |
| |
| .. method:: IncrementalEncoder.setstate(state) |
| |
| Set the state of the encoder to *state*. *state* must be an encoder state |
| returned by :meth:`getstate`. |
| |
| |
| .. _incremental-decoder-objects: |
| |
| IncrementalDecoder Objects |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The :class:`IncrementalDecoder` class is used for decoding an input in multiple |
| steps. It defines the following methods which every incremental decoder must |
| define in order to be compatible with the Python codec registry. |
| |
| |
| .. class:: IncrementalDecoder([errors]) |
| |
| Constructor for an :class:`IncrementalDecoder` instance. |
| |
| 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 :class:`IncrementalDecoder` may implement different error handling schemes |
| by providing the *errors* keyword argument. These parameters are predefined: |
| |
| * ``'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. |
| Assigning to this attribute makes it possible to switch between different error |
| handling strategies during the lifetime of the :class:`IncrementalDecoder` |
| object. |
| |
| The set of allowed values for the *errors* argument can be extended with |
| :func:`register_error`. |
| |
| |
| .. method:: decode(object[, final]) |
| |
| Decodes *object* (taking the current state of the decoder into account) |
| and returns the resulting decoded object. If this is the last call to |
| :meth:`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). |
| |
| |
| .. method:: reset() |
| |
| Reset the decoder to the initial state. |
| |
| |
| .. method:: 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.) |
| |
| |
| .. method:: setstate(state) |
| |
| Set the state of the encoder to *state*. *state* must be a decoder state |
| returned by :meth:`getstate`. |
| |
| |
| The :class:`StreamWriter` and :class:`StreamReader` classes provide generic |
| 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. |
| |
| |
| .. _stream-writer-objects: |
| |
| StreamWriter Objects |
| ^^^^^^^^^^^^^^^^^^^^ |
| |
| 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 |
| compatible with the Python codec registry. |
| |
| |
| .. class:: StreamWriter(stream[, errors]) |
| |
| Constructor for a :class:`StreamWriter` instance. |
| |
| 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. |
| |
| *stream* must be a file-like object open for writing binary data. |
| |
| The :class:`StreamWriter` may implement different error handling schemes by |
| providing the *errors* keyword argument. These parameters are predefined: |
| |
| * ``'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. |
| Assigning to this attribute makes it possible to switch between different error |
| 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) |
| |
| Writes the object's contents encoded to the stream. |
| |
| |
| .. method:: writelines(list) |
| |
| Writes the concatenated list of strings to the stream (possibly by reusing |
| the :meth:`write` method). |
| |
| |
| .. 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 :class:`StreamWriter` must also inherit |
| all other methods and attributes from the underlying stream. |
| |
| |
| .. _stream-reader-objects: |
| |
| StreamReader Objects |
| ^^^^^^^^^^^^^^^^^^^^ |
| |
| 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 |
| compatible with the Python codec registry. |
| |
| |
| .. class:: StreamReader(stream[, errors]) |
| |
| Constructor for a :class:`StreamReader` instance. |
| |
| 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. |
| |
| *stream* must be a file-like object open for reading (binary) data. |
| |
| The :class:`StreamReader` may implement different error handling schemes by |
| providing the *errors* keyword argument. These parameters are defined: |
| |
| * ``'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. |
| Assigning to this attribute makes it possible to switch between different error |
| handling strategies during the lifetime of the :class:`StreamReader` object. |
| |
| The set of allowed values for the *errors* argument can be extended with |
| :func:`register_error`. |
| |
| |
| .. method:: read([size[, chars, [firstline]]]) |
| |
| Decodes data from the stream and returns the resulting object. |
| |
| *chars* indicates the number of characters to read from the |
| stream. :func:`read` will never return more than *chars* characters, but |
| it might return less, if there are not enough characters available. |
| |
| *size* indicates the approximate maximum number of bytes to read from the |
| stream for decoding purposes. The decoder can modify this setting 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 |
| one step. |
| |
| *firstline* 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. |
| |
| |
| .. method:: 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 |
| :meth:`read` method. |
| |
| If *keepends* is false line-endings will be stripped from the lines |
| returned. |
| |
| |
| .. method:: 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* is true. |
| |
| *sizehint*, if given, is passed as the *size* argument to the stream's |
| :meth:`read` method. |
| |
| |
| .. method:: 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 :class:`StreamReader` must also inherit |
| 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: |
| |
| StreamReaderWriter Objects |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| The :class:`StreamReaderWriter` 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 |
| :func:`lookup` function to construct the instance. |
| |
| |
| .. class:: StreamReaderWriter(stream, Reader, Writer, errors) |
| |
| Creates a :class:`StreamReaderWriter` instance. *stream* must be a file-like |
| object. *Reader* and *Writer* must be factory functions or classes providing the |
| :class:`StreamReader` and :class:`StreamWriter` interface resp. Error handling |
| is done in the same way as defined for the stream readers and writers. |
| |
| :class:`StreamReaderWriter` instances define the combined interfaces of |
| :class:`StreamReader` and :class:`StreamWriter` classes. They inherit all other |
| methods and attributes from the underlying stream. |
| |
| |
| .. _stream-recoder-objects: |
| |
| StreamRecoder Objects |
| ^^^^^^^^^^^^^^^^^^^^^ |
| |
| The :class:`StreamRecoder` provide a frontend - backend view of encoding data |
| which is sometimes useful when dealing with different encoding environments. |
| |
| The design is such that one can use the factory functions returned by the |
| :func:`lookup` function to construct the instance. |
| |
| |
| .. class:: StreamRecoder(stream, encode, decode, Reader, Writer, errors) |
| |
| 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 |
| of :meth:`write`) while *Reader* and *Writer* work on the backend (reading and |
| writing to the stream). |
| |
| You can use these objects to do transparent direct recodings from e.g. Latin-1 |
| to UTF-8 and back. |
| |
| *stream* must be a file-like object. |
| |
| *encode*, *decode* must adhere to the :class:`Codec` interface. *Reader*, |
| *Writer* must be factory functions or classes providing objects of the |
| :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 |
| writers. |
| |
| |
| :class:`StreamRecoder` instances define the combined interfaces of |
| :class:`StreamReader` and :class:`StreamWriter` classes. They inherit all other |
| methods and attributes from the underlying stream. |
| |
| |
| .. _encodings-overview: |
| |
| Encodings and Unicode |
| --------------------- |
| |
| Strings are stored internally as sequences of codepoints in range ``0 - 10FFFF`` |
| (see :pep:`393` for more details about the implementation). |
| Once a string object is used outside of CPU and memory, CPU endianness |
| and how these arrays are stored as bytes become an issue. Transforming a |
| string object into a sequence of bytes is called encoding and recreating the |
| string object from the sequence of bytes is known as decoding. There are many |
| different methods for how this transformation can be done (these methods are |
| also called encodings). The simplest method is to map the codepoints 0-255 to |
| the bytes ``0x0``-``0xff``. This means that a string object that contains |
| 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 |
| :exc:`UnicodeEncodeError` that looks like this: ``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 codepoints are |
| mapped to the bytes ``0x0``-``0xff``. To see how this is done simply open |
| e.g. :file:`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 codepoints |
| defined in Unicode. A simple and straightforward way that can store each Unicode |
| code point, is to store each codepoint 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`` as a ``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): |
| |
| +-----------------------------------+----------------------------------------------+ |
| | Range | Encoding | |
| +===================================+==============================================+ |
| | ``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 |
| |
| | LATIN SMALL LETTER I WITH DIAERESIS |
| | RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK |
| | INVERTED QUESTION MARK |
| |
| in iso-8859-1), this increases the probability that a ``utf-8-sig`` encoding can be |
| correctly guessed from the byte sequence. So here the BOM is not used to be able |
| to determine the byte order used for generating the byte sequence, but as a |
| signature that helps in guessing the encoding. On encoding the utf-8-sig codec |
| will write ``0xef``, ``0xbb``, ``0xbf`` as the first three bytes to the file. On |
| decoding ``utf-8-sig`` will skip those three bytes if they appear as the first |
| three bytes in the file. In UTF-8, the use of the BOM is discouraged and |
| should generally be avoided. |
| |
| |
| .. _standard-encodings: |
| |
| Standard Encodings |
| ------------------ |
| |
| 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'`` codec. |
| |
| .. impl-detail:: |
| |
| 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: |
| |
| * an ISO 8859 codeset |
| |
| * a Microsoft Windows code page, which is typically derived from a 8859 codeset, |
| but replaces control characters with additional graphic characters |
| |
| * an IBM EBCDIC code page |
| |
| * an IBM PC code page, which is ASCII compatible |
| |
| .. tabularcolumns:: |l|p{0.3\linewidth}|p{0.3\linewidth}| |
| |
| +-----------------+--------------------------------+--------------------------------+ |
| | Codec | Aliases | Languages | |
| +=================+================================+================================+ |
| | ascii | 646, us-ascii | English | |
| +-----------------+--------------------------------+--------------------------------+ |
| | big5 | big5-tw, csbig5 | Traditional Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | big5hkscs | big5-hkscs, hkscs | Traditional Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp037 | IBM037, IBM039 | English | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp424 | EBCDIC-CP-HE, IBM424 | Hebrew | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp437 | 437, IBM437 | English | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp500 | EBCDIC-CP-BE, EBCDIC-CP-CH, | Western Europe | |
| | | IBM500 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp720 | | Arabic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp737 | | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp775 | IBM775 | Baltic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp850 | 850, IBM850 | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp852 | 852, IBM852 | Central and Eastern Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp855 | 855, IBM855 | Bulgarian, Byelorussian, | |
| | | | Macedonian, Russian, Serbian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp856 | | Hebrew | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp857 | 857, IBM857 | Turkish | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp858 | 858, IBM858 | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp860 | 860, IBM860 | Portuguese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp861 | 861, CP-IS, IBM861 | Icelandic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp862 | 862, IBM862 | Hebrew | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp863 | 863, IBM863 | Canadian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp864 | IBM864 | Arabic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp865 | 865, IBM865 | Danish, Norwegian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp866 | 866, IBM866 | Russian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp869 | 869, CP-GR, IBM869 | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp874 | | Thai | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp875 | | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp932 | 932, ms932, mskanji, ms-kanji | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp949 | 949, ms949, uhc | Korean | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp950 | 950, ms950 | Traditional Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1006 | | Urdu | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1026 | ibm1026 | Turkish | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1140 | ibm1140 | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1250 | windows-1250 | Central and Eastern Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1251 | windows-1251 | Bulgarian, Byelorussian, | |
| | | | Macedonian, Russian, Serbian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1252 | windows-1252 | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1253 | windows-1253 | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1254 | windows-1254 | Turkish | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1255 | windows-1255 | Hebrew | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1256 | windows-1256 | Arabic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1257 | windows-1257 | Baltic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp1258 | windows-1258 | Vietnamese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | cp65001 | | Windows only: Windows UTF-8 | |
| | | | (``CP_UTF8``) | |
| | | | | |
| | | | .. versionadded:: 3.3 | |
| +-----------------+--------------------------------+--------------------------------+ |
| | euc_jp | eucjp, ujis, u-jis | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | euc_jis_2004 | jisx0213, eucjis2004 | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | euc_jisx0213 | eucjisx0213 | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | euc_kr | euckr, korean, ksc5601, | Korean | |
| | | ks_c-5601, ks_c-5601-1987, | | |
| | | ksx1001, ks_x-1001 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | gb2312 | chinese, csiso58gb231280, euc- | Simplified Chinese | |
| | | cn, euccn, eucgb2312-cn, | | |
| | | gb2312-1980, gb2312-80, iso- | | |
| | | ir-58 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | gbk | 936, cp936, ms936 | Unified Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | gb18030 | gb18030-2000 | Unified Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | hz | hzgb, hz-gb, hz-gb-2312 | Simplified Chinese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp | csiso2022jp, iso2022jp, | Japanese | |
| | | iso-2022-jp | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp_1 | iso2022jp-1, iso-2022-jp-1 | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp_2 | iso2022jp-2, iso-2022-jp-2 | Japanese, Korean, Simplified | |
| | | | Chinese, Western Europe, Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp_2004 | iso2022jp-2004, | Japanese | |
| | | iso-2022-jp-2004 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp_3 | iso2022jp-3, iso-2022-jp-3 | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_jp_ext | iso2022jp-ext, iso-2022-jp-ext | Japanese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso2022_kr | csiso2022kr, iso2022kr, | Korean | |
| | | iso-2022-kr | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | latin_1 | iso-8859-1, iso8859-1, 8859, | West Europe | |
| | | cp819, latin, latin1, L1 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_2 | iso-8859-2, latin2, L2 | Central and Eastern Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_3 | iso-8859-3, latin3, L3 | Esperanto, Maltese | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_4 | iso-8859-4, latin4, L4 | Baltic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_5 | iso-8859-5, cyrillic | Bulgarian, Byelorussian, | |
| | | | Macedonian, Russian, Serbian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_6 | iso-8859-6, arabic | Arabic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_7 | iso-8859-7, greek, greek8 | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_8 | iso-8859-8, hebrew | Hebrew | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_9 | iso-8859-9, latin5, L5 | Turkish | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_10 | iso-8859-10, latin6, L6 | Nordic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_13 | iso-8859-13, latin7, L7 | Baltic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_14 | iso-8859-14, latin8, L8 | Celtic languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_15 | iso-8859-15, latin9, L9 | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | iso8859_16 | iso-8859-16, latin10, L10 | South-Eastern Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | johab | cp1361, ms1361 | Korean | |
| +-----------------+--------------------------------+--------------------------------+ |
| | koi8_r | | Russian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | koi8_u | | Ukrainian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_cyrillic | maccyrillic | Bulgarian, Byelorussian, | |
| | | | Macedonian, Russian, Serbian | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_greek | macgreek | Greek | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_iceland | maciceland | Icelandic | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_latin2 | maclatin2, maccentraleurope | Central and Eastern Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_roman | macroman, macintosh | Western Europe | |
| +-----------------+--------------------------------+--------------------------------+ |
| | mac_turkish | macturkish | Turkish | |
| +-----------------+--------------------------------+--------------------------------+ |
| | ptcp154 | csptcp154, pt154, cp154, | Kazakh | |
| | | cyrillic-asian | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | shift_jis | csshiftjis, shiftjis, sjis, | Japanese | |
| | | s_jis | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | shift_jis_2004 | shiftjis2004, sjis_2004, | Japanese | |
| | | sjis2004 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | shift_jisx0213 | shiftjisx0213, sjisx0213, | Japanese | |
| | | s_jisx0213 | | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_32 | U32, utf32 | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_32_be | UTF-32BE | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_32_le | UTF-32LE | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_16 | U16, utf16 | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_16_be | UTF-16BE | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_16_le | UTF-16LE | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_7 | U7, unicode-1-1-utf-7 | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_8 | U8, UTF, utf8 | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| | utf_8_sig | | all languages | |
| +-----------------+--------------------------------+--------------------------------+ |
| |
| Python Specific Encodings |
| ------------------------- |
| |
| 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. |
| |
| The following codecs provide :class:`str` to :class:`bytes` encoding and |
| :term:`bytes-like object` to :class:`str` decoding, similar to the Unicode text |
| encodings. |
| |
| .. tabularcolumns:: |l|p{0.3\linewidth}|p{0.3\linewidth}| |
| |
| +--------------------+---------+---------------------------+ |
| | Codec | Aliases | Purpose | |
| +====================+=========+===========================+ |
| | idna | | Implements :rfc:`3490`, | |
| | | | see also | |
| | | | :mod:`encodings.idna` | |
| +--------------------+---------+---------------------------+ |
| | mbcs | dbcs | Windows only: Encode | |
| | | | operand according to the | |
| | | | ANSI codepage (CP_ACP) | |
| +--------------------+---------+---------------------------+ |
| | palmos | | Encoding of PalmOS 3.5 | |
| +--------------------+---------+---------------------------+ |
| | punycode | | Implements :rfc:`3492` | |
| +--------------------+---------+---------------------------+ |
| | raw_unicode_escape | | Produce a string that is | |
| | | | suitable as raw Unicode | |
| | | | literal in Python source | |
| | | | code | |
| +--------------------+---------+---------------------------+ |
| | undefined | | Raise an exception for | |
| | | | all conversions. Can be | |
| | | | used as the system | |
| | | | encoding if no automatic | |
| | | | coercion between byte and | |
| | | | Unicode strings is | |
| | | | desired. | |
| +--------------------+---------+---------------------------+ |
| | unicode_escape | | Produce a string that is | |
| | | | suitable as Unicode | |
| | | | literal in Python source | |
| | | | code | |
| +--------------------+---------+---------------------------+ |
| | unicode_internal | | Return the internal | |
| | | | representation of the | |
| | | | operand | |
| | | | | |
| | | | .. deprecated:: 3.3 | |
| +--------------------+---------+---------------------------+ |
| |
| The following codecs provide :term:`bytes-like object` to :class:`bytes` |
| mappings. |
| |
| |
| .. tabularcolumns:: |l|L|L| |
| |
| +----------------------+---------------------------+------------------------------+ |
| | Codec | Purpose | Encoder/decoder | |
| +======================+===========================+==============================+ |
| | base64_codec [#b64]_ | Convert operand to MIME | :meth:`base64.b64encode`, | |
| | | base64 (the result always | :meth:`base64.b64decode` | |
| | | includes a trailing | | |
| | | ``'\n'``) | | |
| +----------------------+---------------------------+------------------------------+ |
| | bz2_codec | Compress the operand | :meth:`bz2.compress`, | |
| | | using bz2 | :meth:`bz2.decompress` | |
| +----------------------+---------------------------+------------------------------+ |
| | hex_codec | Convert operand to | :meth:`base64.b16encode`, | |
| | | hexadecimal | :meth:`base64.b16decode` | |
| | | representation, with two | | |
| | | digits per byte | | |
| +----------------------+---------------------------+------------------------------+ |
| | quopri_codec | Convert operand to MIME | :meth:`quopri.encodestring`, | |
| | | quoted printable | :meth:`quopri.decodestring` | |
| +----------------------+---------------------------+------------------------------+ |
| | uu_codec | Convert the operand using | :meth:`uu.encode`, | |
| | | uuencode | :meth:`uu.decode` | |
| +----------------------+---------------------------+------------------------------+ |
| | zlib_codec | Compress the operand | :meth:`zlib.compress`, | |
| | | using gzip | :meth:`zlib.decompress` | |
| +----------------------+---------------------------+------------------------------+ |
| |
| .. [#b64] Rather than accepting any :term:`bytes-like object`, |
| ``'base64_codec'`` accepts only :class:`bytes` and :class:`bytearray` for |
| encoding and only :class:`bytes`, :class:`bytearray`, and ASCII-only |
| instances of :class:`str` for decoding |
| |
| |
| The following codecs provide :class:`str` to :class:`str` mappings. |
| |
| .. tabularcolumns:: |l|L| |
| |
| +--------------------+---------------------------+ |
| | Codec | Purpose | |
| +====================+===========================+ |
| | rot_13 | Returns the Caesar-cypher | |
| | | encryption of the operand | |
| +--------------------+---------------------------+ |
| |
| .. versionadded:: 3.2 |
| bytes-to-bytes and str-to-str codecs. |
| |
| |
| :mod:`encodings.idna` --- Internationalized Domain Names in Applications |
| ------------------------------------------------------------------------ |
| |
| .. module:: encodings.idna |
| :synopsis: Internationalized Domain Names implementation |
| .. moduleauthor:: Martin v. Löwis |
| |
| This module implements :rfc:`3490` (Internationalized Domain Names in |
| Applications) and :rfc:`3492` (Nameprep: A Stringprep Profile for |
| Internationalized Domain Names (IDN)). It builds upon the ``punycode`` encoding |
| and :mod:`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 :mailheader:`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 :mod:`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 :mod:`http.client` and :mod:`ftplib`, accept Unicode host |
| names (:mod:`http.client` then also transparently sends an IDNA hostname in the |
| :mailheader:`Host` field if it sends that field at all). |
| |
| .. _section 3.1: http://tools.ietf.org/html/rfc3490#section-3.1 |
| |
| 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. |
| |
| The module :mod:`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. |
| |
| |
| .. function:: nameprep(label) |
| |
| Return the nameprepped version of *label*. The implementation currently assumes |
| query strings, so ``AllowUnassigned`` is true. |
| |
| |
| .. function:: ToASCII(label) |
| |
| Convert a label to ASCII, as specified in :rfc:`3490`. ``UseSTD3ASCIIRules`` is |
| assumed to be false. |
| |
| |
| .. function:: ToUnicode(label) |
| |
| Convert a label to Unicode, as specified in :rfc:`3490`. |
| |
| |
| :mod:`encodings.mbcs` --- Windows ANSI codepage |
| ----------------------------------------------- |
| |
| .. module:: encodings.mbcs |
| :synopsis: Windows ANSI codepage |
| |
| Encode operand according to the ANSI codepage (CP_ACP). |
| |
| Availability: Windows only. |
| |
| .. versionchanged:: 3.3 |
| Support any error handler. |
| |
| .. versionchanged:: 3.2 |
| Before 3.2, the *errors* argument was ignored; ``'replace'`` was always used |
| to encode, and ``'ignore'`` to decode. |
| |
| |
| :mod:`encodings.utf_8_sig` --- UTF-8 codec with BOM signature |
| ------------------------------------------------------------- |
| |
| .. module:: encodings.utf_8_sig |
| :synopsis: UTF-8 codec with BOM signature |
| .. moduleauthor:: Walter Dörwald |
| |
| 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. |
| |