# `codecs` — Registre des codecs et classes de base associées

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 lève `ValueError` (ou une sous-classe spécifique du codec, telle que `UnicodeEncodeError`). 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 lève `ValueError` (ou une sous-classe spécifique du codec, telle que `UnicodeDecodeError`). 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, une `LookupError` est levée. Sinon, l'objet `CodecInfo` 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()` et `decode()` 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` et `IncrementalDecoder`. 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` et `StreamReader`, 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 return `None`.

  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.

  Nouveau 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-in `open()` 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 une `ValueError` 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.

`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 une `ValueError` 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 que `base64_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 que `rot_13`, bien que `rot_13` puisse être utilisé de manière équivalente avec `iterencode()`.

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 soit `BOM_UTF16_BE`, soit `BOM_UTF16_LE` selon le boutisme natif de la plateforme, `BOM` est un alias pour `BOM_UTF16`, `BOM_LE` pour `BOM_UTF16_LE` et `BOM_BE` pour `BOM_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 &#223;, &#9836;'

The following error handlers can be used with all Python Standard Encodings codecs:

Valeur | Signification
--- | ---
`'strict'` | Raise `UnicodeError` (or a subclass), this is the default. Implemented in `strict_errors()`.
`'ignore'` | Ignore les données incorrectement formatées et continue sans rien signaler. Implémenté dans `ignore_errors()`.
`'replace'` | Replace with a replacement marker. On encoding, use `?` (ASCII character). On decoding, use `�` (U+FFFD, the official REPLACEMENT CHARACTER). Implemented in `replace_errors()`.
`'backslashreplace'` | Replace with backslashed escape sequences. On encoding, use hexadecimal form of Unicode code point with formats `\xhh` `\uxxxx` `\Uxxxxxxxx`. On decoding, use hexadecimal form of byte value with format `\xhh`. Implemented in `backslashreplace_errors()`.
`'surrogateescape'` | Lors du décodage, remplace un octet par un code de substitution individuel allant de `U+DC80` à `U+DCFF`. Ce code est reconverti vers l'octet de départ quand le gestionnaire d'erreurs `'surrogateescape'` est utilisé pour l'encodage des données (voir la PEP 383 pour plus de détails).

The following error handlers are only applicable to encoding (within text encodings):

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

En plus, le gestionnaire d'erreurs suivant est spécifique aux codecs suivants :

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

Nouveau 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.

Nouveau 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 either `str` or `bytes`. If the replacement is bytes, the encoder will simply copy them into the output buffer. If the replacement is a string, the encoder will encode the replacement. Encoding continues on original input at the specified position. Negative position values will be treated as being relative to the end of the input string. If the resulting position is out of bound an `IndexError` will be raised.

  Decoding and translating works similarly, except `UnicodeDecodeError` or `UnicodeTranslateError` will be passed to the handler and that the replacement from the error handler will be put into the output directly.

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

`codecs.``lookup_error`(name)

  Return the error handler previously registered under the name name.

  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}` .

  Nouveau 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:

`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` or `iso-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. Use `StreamWriter` for codecs which have to keep state in order to make encoding efficient.

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

`Codec.``decode`(input, errors='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. Use `StreamReader` for codecs which have to keep state in order to make decoding efficient.

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

### 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 is `0` it must be possible to set the decoder to the state which has no input buffered and `0` as the additional state info, so that feeding the previously buffered input to the decoder returns it to the previous state without producing any output. (Additional state info that is more complicated than integers can be converted into an integer by marshaling/pickling the info and encoding the bytes of the resulting string into an integer.)

  `setstate`(state)

    Set the state of the decoder to state. state must be a decoder state returned by `getstate()`.

### 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 the `StreamReader` and `StreamWriter` interface resp. Error handling is done in the same way as defined for the stream readers and writers.

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

#### 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 calling `read()` and `write()`, 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 the `StreamReader` and `StreamWriter` interface respectively.

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

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

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

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

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

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

> LATIN SMALL LETTER I WITH DIAERESIS
> RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK
> INVERTED QUESTION MARK

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

## 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 Nouveau 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 | Japanese
cp949 | 949, ms949, uhc | Korean
cp950 | 950, ms950 | Chinois Traditionnel
cp1006 |  | Urdu
cp1026 | ibm1026 | Turc
cp1125 | 1125, ibm1125, cp866u, ruscii | Ukrainian Nouveau 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 Nouveau dans la version 3.5.
koi8_u |  | Ukrainian
kz1048 | kz_1048, strk1048_2002, rk1048 | Kazakh Nouveau 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 `encodings.idna`. Only `errors='strict'` is supported.
mbcs | ansi, dbcs | Windows only: Encode the operand according to the ANSI codepage (CP_ACP).
oem |  | Windows only: Encode the operand according to the OEM codepage (CP_OEMCP). Nouveau 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 `\uXXXX` and `\UXXXXXXXX` for other code points. Existing backslashes are not escaped in any way. It is used in the Python pickle protocol.
undefined |  | Raise an exception for all conversions, even empty strings. The error handler is ignored.
unicode_escape |  | Encoding suitable as the contents of a Unicode literal in ASCII-encoded Python source code, except that quotes are not escaped. Decode from Latin-1 source code. Beware that Python source code actually uses UTF-8 by default.

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 `'\n'`). Modifié dans la version 3.4: accepts any bytes-like object as input for encoding and decoding | `base64.encodebytes()` / `base64.decodebytes()`
bz2_codec | bz2 | Compress the operand using bz2. | `bz2.compress()` / `bz2.decompress()`
hex_codec | hex | Convert the operand to hexadecimal representation, with two digits per byte. | `binascii.b2a_hex()` / `binascii.a2b_hex()`
quopri_codec | quopri, quotedprintable, quoted_printable | Convert the operand to MIME quoted printable. | `quopri.encode()` with `quotetabs=True` / `quopri.decode()`
uu_codec | uu | Convert the operand using uuencode. | `uu.encode()` / `uu.decode()`
zlib_codec | zip, zlib | Compress the operand using gzip. | `zlib.compress()` / `zlib.decompress()`

1

  In addition to bytes-like objects, `'base64_codec'` also accepts ASCII-only instances of `str` for decoding

Nouveau 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.

Nouveau 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.idna.``ToASCII`(label)

  Convert a label to ASCII, as specified in RFC 3490. `UseSTD3ASCIIRules` is assumed to be false.

`encodings.idna.``ToUnicode`(label)

  Convert a label to Unicode, as specified in RFC 3490.

## `encodings.mbcs` --- Windows ANSI codepage

This module implements the ANSI codepage (CP_ACP).

Disponibilité : Windows uniquement.

Modifié dans la version 3.3: Support any error handler.

Modifié dans la version 3.2: Before 3.2, the errors argument was ignored; `'replace'` was always used to encode, and `'ignore'` to decode.

## `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.