codecs
--- Codec registry and base classes¶
Code source : Lib/codecs.py
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. Most standard codecs
are text encodings, which encode text to bytes (and
decode bytes to text), 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 be used specifically with
text encodings or with codecs that encode to
bytes
.
Le module définit les fonctions suivantes pour encoder et décoder à l'aide de n'importe quel codec :
- codecs.encode(obj, encoding='utf-8', errors='strict')¶
Encode obj en utilisant le codec enregistré pour encoding.
Vous pouvez spécifier errors pour définir la façon de gérer les erreurs. Le gestionnaire d'erreurs par défaut est
'strict'
, ce qui veut dire qu'une erreur lors de l'encodage lèveValueError
(ou une sous-classe spécifique du codec, telle queUnicodeEncodeError
). Référez-vous aux classes de base des codecs pour plus d'informations sur la gestion des erreurs par les codecs.
- codecs.decode(obj, encoding='utf-8', errors='strict')¶
Décode obj en utilisant le codec enregistré pour encoding.
Vous pouvez spécifier errors pour définir la façon de gérer les erreurs. Le gestionnaire d'erreurs par défaut est
'strict'
, ce qui veut dire qu'une erreur lors du décodage lèveValueError
(ou une sous-classe spécifique du codec, telle queUnicodeDecodeError
). Référez-vous aux classes de base des codecs pour plus d'informations sur la gestion des erreurs par les codecs.
Les détails complets de chaque codec peuvent être examinés directement :
- codecs.lookup(encoding)¶
Recherche les informations relatives au codec dans le registre des codecs de Python et renvoie l'objet
CodecInfo
tel que défini ci-dessous.Les encodeurs sont recherchés en priorité dans le cache du registre. S'ils n'y sont pas, la liste des fonctions de recherche enregistrées est passée en revue. Si aucun objet
CodecInfo
n'est trouvé, uneLookupError
est levée. Sinon, l'objetCodecInfo
est mis en cache et renvoyé vers l'appelant.
- class codecs.CodecInfo(encode, decode, streamreader=None, streamwriter=None, incrementalencoder=None, incrementaldecoder=None, name=None)¶
Les détails d'un codec trouvé dans le registre des codecs. Les arguments du constructeur sont stockés dans les attributs éponymes :
- name¶
Le nom de l'encodeur.
- encode¶
- decode¶
Les fonctions d'encodage et de décodage. Ces fonctions ou méthodes doivent avoir la même interface que les méthodes
encode()
etdecode()
des instances de Codec (voir Interface des codecs). Les fonctions et méthodes sont censées fonctionner sans état interne.
- incrementalencoder¶
- incrementaldecoder¶
Classes d'encodeurs et de décodeurs incrémentaux ou fonctions usines. Elles doivent avoir respectivement les mêmes interfaces que celles définies par les classes de base
IncrementalEncoder
etIncrementalDecoder
. Les codecs incrémentaux peuvent conserver des états internes.
- streamwriter¶
- streamreader¶
Classes d'écriture et de lecture de flux ou fonctions usines. Elles doivent avoir les mêmes interfaces que celles définies par les classes de base
StreamWriter
etStreamReader
, respectivement. Les codecs de flux peuvent conserver un état interne.
Pour simplifier l'accès aux différents composants du codec, le module fournit les fonctions supplémentaires suivantes qui utilisent lookup()
pour la recherche du codec :
- codecs.getencoder(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa fonction d'encodage.
Lève une
LookupError
si l'encodage encoding n'est pas trouvé.
- codecs.getdecoder(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa fonction de décodage.
Lève une
LookupError
si l'encodage encoding n'est pas trouvé.
- codecs.getincrementalencoder(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa classe d'encodage incrémental ou la fonction usine.
Lève une
LookupError
si l'encodage encoding n'est pas trouvé ou si le codec ne gère pas l'encodage incrémental.
- codecs.getincrementaldecoder(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa classe de décodage incrémental ou la fonction usine.
Lève une
LookupError
si l'encodage encoding n'est pas trouvé ou si le codec ne gère pas le décodage incrémental.
- codecs.getreader(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa classe
StreamReader
ou la fonction usine.Lève une
LookupError
si l'encodage encoding n'est pas trouvé.
- codecs.getwriter(encoding)¶
Recherche le codec pour l'encodage encoding et renvoie sa classe
StreamWriter
ou la fonction usine.Lève une
LookupError
si l'encodage encoding n'est pas trouvé.
Les codecs personnalisés sont mis à disposition en enregistrant une fonction de recherche de codecs adaptée :
- codecs.register(search_function)¶
Register a codec search function. Search functions are expected to take one argument, being the encoding name in all lower case letters with hyphens and spaces converted to underscores, and return a
CodecInfo
object. In case a search function cannot find a given encoding, it should returnNone
.Modifié dans la version 3.9: Hyphens and spaces are converted to underscore.
- codecs.unregister(search_function)¶
Unregister a codec search function and clear the registry's cache. If the search function is not registered, do nothing.
Ajouté dans la version 3.10.
Alors qu'il est recommandé d'utiliser la fonction native open()
et le module associé io
pour travailler avec des fichiers texte encodés, le présent module fournit des fonctions et classes utilitaires supplémentaires qui permettent l'utilisation d'une plus large gamme de codecs si vous travaillez avec des fichiers binaires :
- codecs.open(filename, mode='r', encoding=None, errors='strict', buffering=-1)¶
Ouvre un fichier encodé en utilisant le mode donné et renvoie une instance de
StreamReaderWriter
, permettant un encodage-décodage transparent. Le mode de fichier par défaut est'r'
, ce qui signifie que le fichier est ouvert en lecture.Note
If encoding is not
None
, then the underlying encoded files are always opened in binary mode. No automatic conversion of'\n'
is done on reading and writing. The mode argument may be any binary mode acceptable to the built-inopen()
function; the'b'
is automatically added.encoding spécifie l'encodage à utiliser pour le fichier. Tout encodage qui encode et décode des octets (type bytes) est autorisé et les types de données pris en charge par les méthodes relatives aux fichiers dépendent du codec utilisé.
errors peut être spécifié pour définir la gestion des erreurs. La valeur par défaut est
'strict'
, ce qui lève uneValueError
en cas d'erreur lors du codage.buffering a la même signification que pour la fonction native
open()
. Il vaut-1
par défaut, ce qui signifie que la taille par défaut du tampon est utilisée.Modifié dans la version 3.11: le mode
'U`
a été enlevé.
- codecs.EncodedFile(file, data_encoding, file_encoding=None, errors='strict')¶
Renvoie une instance de
StreamRecoder
, version encapsulée de file qui fournit un transcodage transparent. Le fichier original est fermé quand la version encapsulée est fermée.Les données écrites dans un fichier encapsulant sont décodées en fonction du data_encoding spécifié puis écrites vers le fichier original en tant que bytes en utilisant file_encoding. Les octets lus dans le fichier original sont décodés conformément à file_encoding et le résultat est encodé en utilisant data_encoding.
Si file_encoding n'est pas spécifié, la valeur par défaut est data_encoding.
errors peut être spécifié pour définir la gestion des erreurs. La valeur par défaut est
'strict'
, ce qui lève uneValueError
en cas d'erreur lors du codage.
- codecs.iterencode(iterator, encoding, errors='strict', **kwargs)¶
Utilise un encodeur incrémental pour encoder de manière itérative l'entrée fournie par iterator. Cette fonction est un générateur. L'argument errors (ainsi que tout autre argument passé par son nom) est transmis à l'encodeur incrémental.
Cette fonction nécessite que le codec accepte les objets texte (classe
str
) en entrée. Par conséquent, il ne prend pas en charge les encodeurs bytes vers bytes tels quebase64_codec
.
- codecs.iterdecode(iterator, encoding, errors='strict', **kwargs)¶
Utilise un décodeur incrémental pour décoder de manière itérative l'entrée fournie par iterator. Cette fonction est un générateur. L'argument errors (ainsi que tout autre argument passé par son nom) est transmis au décodeur incrémental.
Cette fonction requiert que le codec accepte les objets
bytes
en entrée. Par conséquent, elle ne prend pas en charge les encodeurs de texte vers texte tels querot_13
, bien querot_13
puisse être utilisé de manière équivalente aveciterencode()
.
Le module fournit également les constantes suivantes qui sont utiles pour lire et écrire les fichiers dépendants de la plateforme :
- codecs.BOM¶
- codecs.BOM_BE¶
- codecs.BOM_LE¶
- codecs.BOM_UTF8¶
- codecs.BOM_UTF16¶
- codecs.BOM_UTF16_BE¶
- codecs.BOM_UTF16_LE¶
- codecs.BOM_UTF32¶
- codecs.BOM_UTF32_BE¶
- codecs.BOM_UTF32_LE¶
Ces constantes définissent diverses séquences d'octets, les marques d'ordre d'octets (BOM pour byte order mark en anglais) Unicode pour plusieurs encodages. Elles sont utilisées dans les flux de données UTF-16 et UTF-32 pour indiquer l'ordre des octets utilisé, et dans UTF-8 comme signature Unicode.
BOM_UTF16
vaut soitBOM_UTF16_BE
, soitBOM_UTF16_LE
selon le boutisme natif de la plateforme,BOM
est un alias pourBOM_UTF16
,BOM_LE
pourBOM_UTF16_LE
etBOM_BE
pourBOM_UTF16_BE
. Les autres sont les marques BOM dans les encodages UTF-8 et UTF-32.
Classes de base de codecs¶
Le module codecs
définit un ensemble de classes de base qui spécifient les interfaces pour travailler avec des objets codecs et qui peuvent également être utilisées comme base pour des implémentations de codecs personnalisés.
Chaque codec doit définir quatre interfaces pour être utilisable comme codec en Python : codeur sans état, décodeur sans état, lecteur de flux et écrivain de flux. Le lecteur et l'écrivain de flux réutilisent généralement l'encodeur-décodeur sans état pour implémenter les protocoles de fichiers. Les auteurs de codecs doivent également définir comment le codec gère les erreurs d'encodage et de décodage.
Gestionnaires d'erreurs¶
To simplify and standardize error handling, codecs may implement different error handling schemes by accepting the errors string argument:
>>> 'German ß, ♬'.encode(encoding='ascii', errors='backslashreplace')
b'German \\xdf, \\u266c'
>>> 'German ß, ♬'.encode(encoding='ascii', errors='xmlcharrefreplace')
b'German ß, ♬'
The following error handlers can be used with all Python Standard Encodings codecs:
Valeur |
Signification |
---|---|
|
Raise |
|
Ignore les données incorrectement formatées et continue sans rien signaler. Implémenté dans |
|
Replace with a replacement marker. On
encoding, use |
|
Replace with backslashed escape sequences.
On encoding, use hexadecimal form of Unicode
code point with formats |
|
Lors du décodage, remplace un octet par un code de substitution individuel allant de |
The following error handlers are only applicable to encoding (within text encodings):
Valeur |
Signification |
---|---|
|
Replace with XML/HTML numeric character
reference, which is a decimal form of Unicode
code point with format |
|
Replace with |
En plus, le gestionnaire d'erreurs suivant est spécifique aux codecs suivants :
Valeur |
Codecs |
Signification |
---|---|---|
|
utf-8, utf-16, utf-32, utf-16-be, utf-16-le, utf-32-be, utf-32-le |
Allow encoding and decoding surrogate code
point ( |
Ajouté dans la version 3.1: les gestionnaires d'erreurs 'surrogateescape'
et 'surrogatepass'
.
Modifié dans la version 3.4: The 'surrogatepass'
error handler now works with utf-16* and utf-32*
codecs.
Ajouté dans la version 3.5: le gestionnaire d'erreurs 'namereplace'
.
Modifié dans la version 3.5: The 'backslashreplace'
error handler now works with decoding and
translating.
L'ensemble des valeurs autorisées peut être étendu en enregistrant un nouveau gestionnaire d'erreurs nommé :
- codecs.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
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 eitherstr
orbytes
. 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 anIndexError
will be raised.Decoding and translating works similarly, except
UnicodeDecodeError
orUnicodeTranslateError
will be passed to the handler and that the replacement from the error handler will be put into the output directly.
Previously registered error handlers (including the standard error handlers) can be looked up by name:
- codecs.lookup_error(name)¶
Return the error handler previously registered under the name name.
Raises a
LookupError
in case the handler cannot be found.
The following standard error handlers are also made available as module level functions:
- codecs.strict_errors(exception)¶
Implements the
'strict'
error handling.Each encoding or decoding error raises a
UnicodeError
.
- codecs.ignore_errors(exception)¶
Implements the
'ignore'
error handling.Malformed data is ignored; encoding or decoding is continued without further notice.
- codecs.replace_errors(exception)¶
Implements the
'replace'
error handling.Substitutes
?
(ASCII character) for encoding errors or�
(U+FFFD, the official REPLACEMENT CHARACTER) for decoding errors.
- codecs.backslashreplace_errors(exception)¶
Implements the
'backslashreplace'
error handling.Malformed data is replaced by a backslashed escape sequence. On encoding, use the hexadecimal form of Unicode code point with formats
\xhh
\uxxxx
\Uxxxxxxxx
. On decoding, use the hexadecimal form of byte value with format\xhh
.Modifié dans la version 3.5: Works with decoding and translating.
- codecs.xmlcharrefreplace_errors(exception)¶
Implements the
'xmlcharrefreplace'
error handling (for encoding within text encoding only).The unencodable character is replaced by an appropriate XML/HTML numeric character reference, which is a decimal form of Unicode code point with format
&#num;
.
- codecs.namereplace_errors(exception)¶
Implements the
'namereplace'
error handling (for encoding within text encoding only).The unencodable character is replaced by a
\N{...}
escape sequence. The set of characters that appear in the braces is the Name property from Unicode Character Database. For example, the German lowercase letter'ß'
will be converted to byte sequence\N{LATIN SMALL LETTER SHARP S}
.Ajouté dans la version 3.5.
Stateless Encoding and Decoding¶
The base Codec
class defines these methods which also define the
function interfaces of the stateless encoder and decoder:
- class codecs.Codec¶
- encode(input, errors='strict')¶
Encodes the object input and returns a tuple (output object, length consumed). For instance, text encoding converts a string object to a bytes object using a particular character set encoding (e.g.,
cp1252
oriso-8859-1
).The errors argument defines the error handling to apply. It defaults to
'strict'
handling.The method may not store state in the
Codec
instance. UseStreamWriter
for codecs which have to keep state in order to make encoding efficient.The encoder must be able to handle zero length input and return an empty object of the output object type in this situation.
- decode(input, errors='strict')¶
Decodes the object input and returns a tuple (output object, length consumed). For instance, for a text encoding, decoding converts a bytes object encoded using a particular character set encoding to a string object.
For text encodings and bytes-to-bytes codecs, input must be a bytes object or one which provides the read-only buffer interface -- for example, buffer objects and memory mapped files.
The errors argument defines the error handling to apply. It defaults to
'strict'
handling.The method may not store state in the
Codec
instance. UseStreamReader
for codecs which have to keep state in order to make decoding efficient.The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.
Incremental Encoding and Decoding¶
The IncrementalEncoder
and IncrementalDecoder
classes provide
the basic interface for incremental encoding and decoding. Encoding/decoding the
input isn't done with one call to the stateless encoder/decoder function, but
with multiple calls to the
encode()
/decode()
method of
the incremental encoder/decoder. The incremental encoder/decoder keeps track of
the encoding/decoding process during method calls.
The joined output of calls to the
encode()
/decode()
method is
the same as if all the single inputs were joined into one, and this input was
encoded/decoded with the stateless encoder/decoder.
IncrementalEncoder Objects¶
The IncrementalEncoder
class is used for encoding an input in multiple
steps. It defines the following methods which every incremental encoder must
define in order to be compatible with the Python codec registry.
- class codecs.IncrementalEncoder(errors='strict')¶
Constructor for an
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
IncrementalEncoder
may implement different error handling schemes by providing the errors keyword argument. See Gestionnaires d'erreurs for possible values.The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the
IncrementalEncoder
object.- encode(object, final=False)¶
Encodes object (taking the current state of the encoder into account) and returns the resulting encoded object. If this is the last call to
encode()
final must be true (the default is false).
- reset()¶
Reset the encoder to the initial state. The output is discarded: call
.encode(object, final=True)
, passing an empty byte or text string if necessary, to reset the encoder and to get the output.
- getstate()¶
Return the current state of the encoder which must be an integer. The implementation should make sure that
0
is the most common state. (States that are more complicated than integers can be converted into an integer by marshaling/pickling the state and encoding the bytes of the resulting string into an integer.)
- setstate(state)¶
Set the state of the encoder to state. state must be an encoder state returned by
getstate()
.
IncrementalDecoder Objects¶
The IncrementalDecoder
class is used for decoding an input in multiple
steps. It defines the following methods which every incremental decoder must
define in order to be compatible with the Python codec registry.
- class codecs.IncrementalDecoder(errors='strict')¶
Constructor for an
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
IncrementalDecoder
may implement different error handling schemes by providing the errors keyword argument. See Gestionnaires d'erreurs for possible values.The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the
IncrementalDecoder
object.- decode(object, final=False)¶
Decodes object (taking the current state of the decoder into account) and returns the resulting decoded object. If this is the last call to
decode()
final must be true (the default is false). If final is true the decoder must decode the input completely and must flush all buffers. If this isn't possible (e.g. because of incomplete byte sequences at the end of the input) it must initiate error handling just like in the stateless case (which might raise an exception).
- reset()¶
Reset the decoder to the initial state.
- 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 is0
it must be possible to set the decoder to the state which has no input buffered and0
as the additional state info, so that feeding the previously buffered input to the decoder returns it to the previous state without producing any output. (Additional state info that is more complicated than integers can be converted into an integer by marshaling/pickling the info and encoding the bytes of the resulting string into an integer.)
- setstate(state)¶
Set the state of the decoder to state. state must be a decoder state returned by
getstate()
.
Stream Encoding and Decoding¶
The StreamWriter
and StreamReader
classes provide generic
working interfaces which can be used to implement new encoding submodules very
easily. See encodings.utf_8
for an example of how this is done.
StreamWriter Objects¶
The StreamWriter
class is a subclass of Codec
and defines the
following methods which every stream writer must define in order to be
compatible with the Python codec registry.
- class codecs.StreamWriter(stream, errors='strict')¶
Constructor for a
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.
The stream argument must be a file-like object open for writing text or binary data, as appropriate for the specific codec.
The
StreamWriter
may implement different error handling schemes by providing the errors keyword argument. See Gestionnaires d'erreurs for the standard error handlers the underlying stream codec may support.The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the
StreamWriter
object.- write(object)¶
Writes the object's contents encoded to the stream.
- writelines(list)¶
Writes the concatenated iterable of strings to the stream (possibly by reusing the
write()
method). Infinite or very large iterables are not supported. The standard bytes-to-bytes codecs do not support this method.
- reset()¶
Resets the codec buffers used for keeping internal state.
Calling this method should ensure that the data on the output is put into a clean state that allows appending of new fresh data without having to rescan the whole stream to recover state.
In addition to the above methods, the StreamWriter
must also inherit
all other methods and attributes from the underlying stream.
StreamReader Objects¶
The StreamReader
class is a subclass of Codec
and defines the
following methods which every stream reader must define in order to be
compatible with the Python codec registry.
- class codecs.StreamReader(stream, errors='strict')¶
Constructor for a
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.
The stream argument must be a file-like object open for reading text or binary data, as appropriate for the specific codec.
The
StreamReader
may implement different error handling schemes by providing the errors keyword argument. See Gestionnaires d'erreurs for the standard error handlers the underlying stream codec may support.The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the
StreamReader
object.The set of allowed values for the errors argument can be extended with
register_error()
.- read(size=-1, chars=-1, firstline=False)¶
Decodes data from the stream and returns the resulting object.
The chars argument indicates the number of decoded code points or bytes to return. The
read()
method will never return more data than requested, but it might return less, if there is not enough available.The size argument indicates the approximate maximum number of encoded bytes or code points to read for decoding. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. This parameter is intended to prevent having to decode huge files in one step.
The firstline flag indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines.
The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.
- readline(size=None, keepends=True)¶
Read one line from the input stream and return the decoded data.
size, if given, is passed as size argument to the stream's
read()
method.If keepends is false line-endings will be stripped from the lines returned.
- readlines(sizehint=None, keepends=True)¶
Read all lines available on the input stream and return them as a list of lines.
Line-endings are implemented using the codec's
decode()
method and are included in the list entries if keepends is true.sizehint, if given, is passed as the size argument to the stream's
read()
method.
- reset()¶
Resets the codec buffers used for keeping internal state.
Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.
In addition to the above methods, the StreamReader
must also inherit
all other methods and attributes from the underlying stream.
StreamReaderWriter Objects¶
The StreamReaderWriter
is a convenience class that allows wrapping
streams which work in both read and write modes.
The design is such that one can use the factory functions returned by the
lookup()
function to construct the instance.
- class codecs.StreamReaderWriter(stream, Reader, Writer, errors='strict')¶
Creates a
StreamReaderWriter
instance. stream must be a file-like object. Reader and Writer must be factory functions or classes providing theStreamReader
andStreamWriter
interface resp. Error handling is done in the same way as defined for the stream readers and writers.
StreamReaderWriter
instances define the combined interfaces of
StreamReader
and StreamWriter
classes. They inherit all other
methods and attributes from the underlying stream.
StreamRecoder Objects¶
The StreamRecoder
translates data from one encoding to another,
which is sometimes useful when dealing with different encoding environments.
The design is such that one can use the factory functions returned by the
lookup()
function to construct the instance.
- class codecs.StreamRecoder(stream, encode, decode, Reader, Writer, errors='strict')¶
Creates a
StreamRecoder
instance which implements a two-way conversion: encode and decode work on the frontend — the data visible to code callingread()
andwrite()
, while Reader and Writer work on the backend — the data in stream.You can use these objects to do transparent transcodings, e.g., from Latin-1 to UTF-8 and back.
The stream argument must be a file-like object.
The encode and decode arguments must adhere to the
Codec
interface. Reader and Writer must be factory functions or classes providing objects of theStreamReader
andStreamWriter
interface respectively.Error handling is done in the same way as defined for the stream readers and writers.
StreamRecoder
instances define the combined interfaces of
StreamReader
and StreamWriter
classes. They inherit all other
methods and attributes from the underlying stream.
Encodings and Unicode¶
Strings are stored internally as sequences of code points in
range U+0000
--U+10FFFF
. (See PEP 393 for
more details about the implementation.)
Once a string object is used outside of CPU and memory, endianness
and how these arrays are stored as bytes become an issue. As with other
codecs, serialising a string into a sequence of bytes is known as encoding,
and recreating the string from the sequence of bytes is known as decoding.
There are a variety of different text serialisation codecs, which are
collectivity referred to as text encodings.
The simplest text encoding (called 'latin-1'
or 'iso-8859-1'
) maps
the code points 0--255 to the bytes 0x0
--0xff
, which means that a string
object that contains code points above U+00FF
can't be encoded with this
codec. Doing so will raise a UnicodeEncodeError
that looks
like the following (although the details of the error message may differ):
UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in
position 3: ordinal not in range(256)
.
There's another group of encodings (the so called charmap encodings) that choose
a different subset of all Unicode code points and how these code points are
mapped to the bytes 0x0
--0xff
. To see how this is done simply open
e.g. encodings/cp1252.py
(which is an encoding that is used primarily on
Windows). There's a string constant with 256 characters that shows you which
character is mapped to which byte value.
All of these encodings can only encode 256 of the 1114112 code points
defined in Unicode. A simple and straightforward way that can store each Unicode
code point, is to store each code point as four consecutive bytes. There are two
possibilities: store the bytes in big endian or in little endian order. These
two encodings are called UTF-32-BE
and UTF-32-LE
respectively. Their
disadvantage is that if e.g. you use UTF-32-BE
on a little endian machine you
will always have to swap bytes on encoding and decoding. UTF-32
avoids this
problem: bytes will always be in natural endianness. When these bytes are read
by a CPU with a different endianness, then bytes have to be swapped though. To
be able to detect the endianness of a UTF-16
or UTF-32
byte sequence,
there's the so called BOM ("Byte Order Mark"). This is the Unicode character
U+FEFF
. This character can be prepended to every UTF-16
or UTF-32
byte sequence. The byte swapped version of this character (0xFFFE
) is an
illegal character that may not appear in a Unicode text. So when the
first character in a UTF-16
or UTF-32
byte sequence
appears to be a U+FFFE
the bytes have to be swapped on decoding.
Unfortunately the character U+FEFF
had a second purpose as
a ZERO WIDTH NO-BREAK SPACE
: a character that has no width and doesn't allow
a word to be split. It can e.g. be used to give hints to a ligature algorithm.
With Unicode 4.0 using U+FEFF
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 encode the full range of Unicode
characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues
with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two
parts: marker bits (the most significant bits) and payload bits. The marker bits
are a sequence of zero to four 1
bits followed by a 0
bit. Unicode characters are
encoded like this (with x being payload bits, which when concatenated give the
Unicode character):
Range |
Encoding |
---|---|
|
0xxxxxxx |
|
110xxxxx 10xxxxxx |
|
1110xxxx 10xxxxxx 10xxxxxx |
|
11110xxx 10xxxxxx 10xxxxxx 10xxxxxx |
The least significant bit of the Unicode character is the rightmost x bit.
As UTF-8 is an 8-bit encoding no BOM is required and any U+FEFF
character in
the decoded string (even if it's the first character) is treated as a ZERO
WIDTH NO-BREAK SPACE
.
Without external information it's impossible to reliably determine which
encoding was used for encoding a string. Each charmap encoding can
decode any random byte sequence. However that's not possible with UTF-8, as
UTF-8 byte sequences have a structure that doesn't allow arbitrary byte
sequences. To increase the reliability with which a UTF-8 encoding can be
detected, Microsoft invented a variant of UTF-8 (that Python calls
"utf-8-sig"
) for its Notepad program: Before any of the Unicode characters
is written to the file, a UTF-8 encoded BOM (which looks like this as a byte
sequence: 0xef
, 0xbb
, 0xbf
) is written. As it's rather improbable
that any charmap encoded file starts with these byte values (which would e.g.
map to
LATIN SMALL LETTER I WITH DIAERESISRIGHT-POINTING DOUBLE ANGLE QUOTATION MARKINVERTED 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¶
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.
Particularité de l'implémentation CPython : Some common encodings can bypass the codecs lookup machinery to improve performance. These optimization opportunities are only recognized by CPython for a limited set of (case insensitive) aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, iso8859-1, mbcs (Windows only), ascii, us-ascii, utf-16, utf16, utf-32, utf32, and the same using underscores instead of dashes. Using alternative aliases for these encodings may result in slower execution.
Modifié dans la version 3.6: Optimization opportunity recognized for us-ascii.
Many of the character sets support the same languages. They vary in individual characters (e.g. whether the EURO SIGN is supported or not), and in the assignment of characters to code positions. For the European languages in particular, the following variants typically exist:
an ISO 8859 codeset
a Microsoft Windows code page, which is typically derived from an 8859 codeset, but replaces control characters with additional graphic characters
an IBM EBCDIC code page
an IBM PC code page, which is ASCII compatible
Codec |
Aliases |
Languages |
---|---|---|
ascii |
646, us-ascii |
Anglais |
big5 |
big5-tw, csbig5 |
Chinois Traditionnel |
big5hkscs |
big5-hkscs, hkscs |
Chinois Traditionnel |
cp037 |
IBM037, IBM039 |
Anglais |
cp273 |
273, IBM273, csIBM273 |
Allemand Ajouté dans la version 3.4. |
cp424 |
EBCDIC-CP-HE, IBM424 |
Hébreux |
cp437 |
437, IBM437 |
Anglais |
cp500 |
EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500 |
Europe de l'ouest |
cp720 |
Arabe |
|
cp737 |
Grec |
|
cp775 |
IBM775 |
Langues Baltiques |
cp850 |
850, IBM850 |
Europe de l'ouest |
cp852 |
852, IBM852 |
Europe centrale et Europe de l'Est |
cp855 |
855, IBM855 |
Bulgare, Biélorusse, Macédonien, Russe, Serbe |
cp856 |
Hébreux |
|
cp857 |
857, IBM857 |
Turc |
cp858 |
858, IBM858 |
Europe de l'ouest |
cp860 |
860, IBM860 |
Portugais |
cp861 |
861, CP-IS, IBM861 |
Islandais |
cp862 |
862, IBM862 |
Hébreux |
cp863 |
863, IBM863 |
Canadien |
cp864 |
IBM864 |
Arabe |
cp865 |
865, IBM865 |
Danish, Norwegian |
cp866 |
866, IBM866 |
Russe |
cp869 |
869, CP-GR, IBM869 |
Grec |
cp874 |
Thai |
|
cp875 |
Grec |
|
cp932 |
932, ms932, mskanji, ms-kanji, windows-31j |
Japanese |
cp949 |
949, ms949, uhc |
Korean |
cp950 |
950, ms950 |
Chinois Traditionnel |
cp1006 |
Urdu |
|
cp1026 |
ibm1026 |
Turc |
cp1125 |
1125, ibm1125, cp866u, ruscii |
Ukrainian Ajouté dans la version 3.4. |
cp1140 |
ibm1140 |
Europe de l'ouest |
cp1250 |
windows-1250 |
Europe centrale et Europe de l'Est |
cp1251 |
windows-1251 |
Bulgare, Biélorusse, Macédonien, Russe, Serbe |
cp1252 |
windows-1252 |
Europe de l'ouest |
cp1253 |
windows-1253 |
Grec |
cp1254 |
windows-1254 |
Turc |
cp1255 |
windows-1255 |
Hébreux |
cp1256 |
windows-1256 |
Arabe |
cp1257 |
windows-1257 |
Langues Baltiques |
cp1258 |
windows-1258 |
Vietnamese |
euc_jp |
eucjp, ujis, u-jis |
Japanese |
euc_jis_2004 |
jisx0213, eucjis2004 |
Japanese |
euc_jisx0213 |
eucjisx0213 |
Japanese |
euc_kr |
euckr, korean, ksc5601, ks_c-5601, ks_c-5601-1987, ksx1001, ks_x-1001 |
Korean |
gb2312 |
chinese, csiso58gb231280, euc-cn, euccn, eucgb2312-cn, gb2312-1980, gb2312-80, iso-ir-58 |
Simplified Chinese |
gbk |
936, cp936, ms936 |
Unified Chinese |
gb18030 |
gb18030-2000 |
Unified Chinese |
hz |
hzgb, hz-gb, hz-gb-2312 |
Simplified Chinese |
iso2022_jp |
csiso2022jp, iso2022jp, iso-2022-jp |
Japanese |
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, iso-2022-jp-2004 |
Japanese |
iso2022_jp_3 |
iso2022jp-3, iso-2022-jp-3 |
Japanese |
iso2022_jp_ext |
iso2022jp-ext, iso-2022-jp-ext |
Japanese |
iso2022_kr |
csiso2022kr, iso2022kr, iso-2022-kr |
Korean |
latin_1 |
iso-8859-1, iso8859-1, 8859, cp819, latin, latin1, L1 |
Europe de l'ouest |
iso8859_2 |
iso-8859-2, latin2, L2 |
Europe centrale et Europe de l'Est |
iso8859_3 |
iso-8859-3, latin3, L3 |
Esperanto, Maltese |
iso8859_4 |
iso-8859-4, latin4, L4 |
Langues Baltiques |
iso8859_5 |
iso-8859-5, cyrillic |
Bulgare, Biélorusse, Macédonien, Russe, Serbe |
iso8859_6 |
iso-8859-6, arabic |
Arabe |
iso8859_7 |
iso-8859-7, greek, greek8 |
Grec |
iso8859_8 |
iso-8859-8, hebrew |
Hébreux |
iso8859_9 |
iso-8859-9, latin5, L5 |
Turc |
iso8859_10 |
iso-8859-10, latin6, L6 |
Nordic languages |
iso8859_11 |
iso-8859-11, thai |
Thai languages |
iso8859_13 |
iso-8859-13, latin7, L7 |
Langues Baltiques |
iso8859_14 |
iso-8859-14, latin8, L8 |
Celtic languages |
iso8859_15 |
iso-8859-15, latin9, L9 |
Europe de l'ouest |
iso8859_16 |
iso-8859-16, latin10, L10 |
South-Eastern Europe |
johab |
cp1361, ms1361 |
Korean |
koi8_r |
Russe |
|
koi8_t |
Tajik Ajouté dans la version 3.5. |
|
koi8_u |
Ukrainian |
|
kz1048 |
kz_1048, strk1048_2002, rk1048 |
Kazakh Ajouté dans la version 3.5. |
mac_cyrillic |
maccyrillic |
Bulgare, Biélorusse, Macédonien, Russe, Serbe |
mac_greek |
macgreek |
Grec |
mac_iceland |
maciceland |
Islandais |
mac_latin2 |
maclatin2, maccentraleurope, mac_centeuro |
Europe centrale et Europe de l'Est |
mac_roman |
macroman, macintosh |
Europe de l'ouest |
mac_turkish |
macturkish |
Turc |
ptcp154 |
csptcp154, pt154, cp154, cyrillic-asian |
Kazakh |
shift_jis |
csshiftjis, shiftjis, sjis, s_jis |
Japanese |
shift_jis_2004 |
shiftjis2004, sjis_2004, sjis2004 |
Japanese |
shift_jisx0213 |
shiftjisx0213, sjisx0213, s_jisx0213 |
Japanese |
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, cp65001 |
all languages |
utf_8_sig |
all languages |
Modifié dans la version 3.4: The utf-16* and utf-32* encoders no longer allow surrogate code points
(U+D800
--U+DFFF
) to be encoded.
The utf-32* decoders no longer decode
byte sequences that correspond to surrogate code points.
Modifié dans la version 3.8: cp65001
is now an alias to utf_8
.
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 meaning describes the encoding direction.
Text Encodings¶
The following codecs provide str
to bytes
encoding and
bytes-like object to str
decoding, similar to the Unicode text
encodings.
Codec |
Aliases |
Signification |
---|---|---|
idna |
Implement RFC 3490,
see also
|
|
mbcs |
ansi, dbcs |
Windows only: Encode the operand according to the ANSI codepage (CP_ACP). |
oem |
Windows only: Encode the operand according to the OEM codepage (CP_OEMCP). Ajouté dans la version 3.6. |
|
palmos |
Encoding of PalmOS 3.5. |
|
punycode |
Implement RFC 3492. Stateful codecs are not supported. |
|
raw_unicode_escape |
Latin-1 encoding with
|
|
undefined |
Raise an exception for all conversions, even empty strings. The error handler is ignored. |
|
unicode_escape |
Encoding suitable as the contents of a Unicode literal in ASCII-encoded Python source code, except that quotes are not escaped. Decode from Latin-1 source code. Beware that Python source code actually uses UTF-8 by default. |
Modifié dans la version 3.8: "unicode_internal" codec is removed.
Binary Transforms¶
The following codecs provide binary transforms: bytes-like object
to bytes
mappings. They are not supported by bytes.decode()
(which only produces str
output).
Codec |
Aliases |
Signification |
Encoder / decoder |
---|---|---|---|
base64_codec [1] |
base64, base_64 |
Convert the operand to
multiline MIME base64 (the
result always includes a
trailing Modifié dans la version 3.4: accepts any bytes-like object as input for encoding and decoding |
|
bz2_codec |
bz2 |
Compress the operand using bz2. |
|
hex_codec |
hex |
Convert the operand to hexadecimal representation, with two digits per byte. |
|
quopri_codec |
quopri, quotedprintable, quoted_printable |
Convert the operand to MIME quoted printable. |
|
uu_codec |
uu |
Convert the operand using uuencode. |
|
zlib_codec |
zip, zlib |
Compress the operand using gzip. |
Ajouté dans la version 3.2: Restoration of the binary transforms.
Modifié dans la version 3.4: Restoration of the aliases for the binary transforms.
Text Transforms¶
The following codec provides a text transform: a str
to str
mapping. It is not supported by str.encode()
(which only produces
bytes
output).
Codec |
Aliases |
Signification |
---|---|---|
rot_13 |
rot13 |
Return the Caesar-cypher encryption of the operand. |
Ajouté dans la version 3.2: Restoration of the rot_13
text transform.
Modifié dans la version 3.4: Restoration of the rot13
alias.
encodings.idna
--- Internationalized Domain Names in Applications¶
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 stringprep
.
If you need the IDNA 2008 standard from RFC 5891 and RFC 5895, use the third-party idna module.
These RFCs together define a protocol to support non-ASCII characters in domain
names. A domain name containing non-ASCII characters (such as
www.Alliancefrançaise.nu
) is converted into an ASCII-compatible encoding
(ACE, such as www.xn--alliancefranaise-npb.nu
). The ACE form of the domain
name is then used in all places where arbitrary characters are not allowed by
the protocol, such as DNS queries, HTTP Host fields, and so
on. This conversion is carried out in the application; if possible invisible to
the user: The application should transparently convert Unicode domain labels to
IDNA on the wire, and convert back ACE labels to Unicode before presenting them
to the user.
Python supports this conversion in several ways: the idna
codec performs
conversion between Unicode and ACE, separating an input string into labels
based on the separator characters defined in section 3.1 of RFC 3490
and converting each label to ACE as required, and conversely separating an input
byte string into labels based on the .
separator and converting any ACE
labels found into unicode. Furthermore, the socket
module
transparently converts Unicode host names to ACE, so that applications need not
be concerned about converting host names themselves when they pass them to the
socket module. On top of that, modules that have host names as function
parameters, such as http.client
and ftplib
, accept Unicode host
names (http.client
then also transparently sends an IDNA hostname in the
Host field if it sends that field at all).
When receiving host names from the wire (such as in reverse name lookup), no automatic conversion to Unicode is performed: applications wishing to present such host names to the user should decode them to Unicode.
The module encodings.idna
also implements the nameprep procedure, which
performs certain normalizations on host names, to achieve case-insensitivity of
international domain names, and to unify similar characters. The nameprep
functions can be used directly if desired.
- encodings.idna.nameprep(label)¶
Return the nameprepped version of label. The implementation currently assumes query strings, so
AllowUnassigned
is true.
encodings.mbcs
--- Windows ANSI codepage¶
This module implements the ANSI codepage (CP_ACP).
Availability: Windows.
Modifié dans la version 3.2: Before 3.2, the errors argument was ignored; 'replace'
was always used
to encode, and 'ignore'
to decode.
Modifié dans la version 3.3: Support any error handler.
encodings.utf_8_sig
--- UTF-8 codec with BOM signature¶
This module implements a variant of the UTF-8 codec. On encoding, a UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this is only done once (on the first write to the byte stream). On decoding, an optional UTF-8 encoded BOM at the start of the data will be skipped.