1:mod:`codecs` --- Codec registry and base classes 2================================================= 3 4.. module:: codecs 5 :synopsis: Encode and decode data and streams. 6 7.. moduleauthor:: Marc-André Lemburg <mal@lemburg.com> 8.. sectionauthor:: Marc-André Lemburg <mal@lemburg.com> 9.. sectionauthor:: Martin v. Löwis <martin@v.loewis.de> 10 11**Source code:** :source:`Lib/codecs.py` 12 13.. index:: 14 single: Unicode 15 single: Codecs 16 pair: Codecs; encode 17 pair: Codecs; decode 18 single: streams 19 pair: stackable; streams 20 21-------------- 22 23This module defines base classes for standard Python codecs (encoders and 24decoders) and provides access to the internal Python codec registry, which 25manages the codec and error handling lookup process. Most standard codecs 26are :term:`text encodings <text encoding>`, which encode text to bytes, 27but there are also codecs provided that encode text to text, and bytes to 28bytes. Custom codecs may encode and decode between arbitrary types, but some 29module features are restricted to use specifically with 30:term:`text encodings <text encoding>`, or with codecs that encode to 31:class:`bytes`. 32 33The module defines the following functions for encoding and decoding with 34any codec: 35 36.. function:: encode(obj, encoding='utf-8', errors='strict') 37 38 Encodes *obj* using the codec registered for *encoding*. 39 40 *Errors* may be given to set the desired error handling scheme. The 41 default error handler is ``'strict'`` meaning that encoding errors raise 42 :exc:`ValueError` (or a more codec specific subclass, such as 43 :exc:`UnicodeEncodeError`). Refer to :ref:`codec-base-classes` for more 44 information on codec error handling. 45 46.. function:: decode(obj, encoding='utf-8', errors='strict') 47 48 Decodes *obj* using the codec registered for *encoding*. 49 50 *Errors* may be given to set the desired error handling scheme. The 51 default error handler is ``'strict'`` meaning that decoding errors raise 52 :exc:`ValueError` (or a more codec specific subclass, such as 53 :exc:`UnicodeDecodeError`). Refer to :ref:`codec-base-classes` for more 54 information on codec error handling. 55 56The full details for each codec can also be looked up directly: 57 58.. function:: lookup(encoding) 59 60 Looks up the codec info in the Python codec registry and returns a 61 :class:`CodecInfo` object as defined below. 62 63 Encodings are first looked up in the registry's cache. If not found, the list of 64 registered search functions is scanned. If no :class:`CodecInfo` object is 65 found, a :exc:`LookupError` is raised. Otherwise, the :class:`CodecInfo` object 66 is stored in the cache and returned to the caller. 67 68.. class:: CodecInfo(encode, decode, streamreader=None, streamwriter=None, incrementalencoder=None, incrementaldecoder=None, name=None) 69 70 Codec details when looking up the codec registry. The constructor 71 arguments are stored in attributes of the same name: 72 73 74 .. attribute:: name 75 76 The name of the encoding. 77 78 79 .. attribute:: encode 80 decode 81 82 The stateless encoding and decoding functions. These must be 83 functions or methods which have the same interface as 84 the :meth:`~Codec.encode` and :meth:`~Codec.decode` methods of Codec 85 instances (see :ref:`Codec Interface <codec-objects>`). 86 The functions or methods are expected to work in a stateless mode. 87 88 89 .. attribute:: incrementalencoder 90 incrementaldecoder 91 92 Incremental encoder and decoder classes or factory functions. 93 These have to provide the interface defined by the base classes 94 :class:`IncrementalEncoder` and :class:`IncrementalDecoder`, 95 respectively. Incremental codecs can maintain state. 96 97 98 .. attribute:: streamwriter 99 streamreader 100 101 Stream writer and reader classes or factory functions. These have to 102 provide the interface defined by the base classes 103 :class:`StreamWriter` and :class:`StreamReader`, respectively. 104 Stream codecs can maintain state. 105 106To simplify access to the various codec components, the module provides 107these additional functions which use :func:`lookup` for the codec lookup: 108 109.. function:: getencoder(encoding) 110 111 Look up the codec for the given encoding and return its encoder function. 112 113 Raises a :exc:`LookupError` in case the encoding cannot be found. 114 115 116.. function:: getdecoder(encoding) 117 118 Look up the codec for the given encoding and return its decoder function. 119 120 Raises a :exc:`LookupError` in case the encoding cannot be found. 121 122 123.. function:: getincrementalencoder(encoding) 124 125 Look up the codec for the given encoding and return its incremental encoder 126 class or factory function. 127 128 Raises a :exc:`LookupError` in case the encoding cannot be found or the codec 129 doesn't support an incremental encoder. 130 131 132.. function:: getincrementaldecoder(encoding) 133 134 Look up the codec for the given encoding and return its incremental decoder 135 class or factory function. 136 137 Raises a :exc:`LookupError` in case the encoding cannot be found or the codec 138 doesn't support an incremental decoder. 139 140 141.. function:: getreader(encoding) 142 143 Look up the codec for the given encoding and return its :class:`StreamReader` 144 class or factory function. 145 146 Raises a :exc:`LookupError` in case the encoding cannot be found. 147 148 149.. function:: getwriter(encoding) 150 151 Look up the codec for the given encoding and return its :class:`StreamWriter` 152 class or factory function. 153 154 Raises a :exc:`LookupError` in case the encoding cannot be found. 155 156Custom codecs are made available by registering a suitable codec search 157function: 158 159.. function:: register(search_function) 160 161 Register a codec search function. Search functions are expected to take one 162 argument, being the encoding name in all lower case letters, and return a 163 :class:`CodecInfo` object. In case a search function cannot find 164 a given encoding, it should return ``None``. 165 166 .. note:: 167 168 Search function registration is not currently reversible, 169 which may cause problems in some cases, such as unit testing or 170 module reloading. 171 172While the builtin :func:`open` and the associated :mod:`io` module are the 173recommended approach for working with encoded text files, this module 174provides additional utility functions and classes that allow the use of a 175wider range of codecs when working with binary files: 176 177.. function:: open(filename, mode='r', encoding=None, errors='strict', buffering=1) 178 179 Open an encoded file using the given *mode* and return an instance of 180 :class:`StreamReaderWriter`, providing transparent encoding/decoding. 181 The default file mode is ``'r'``, meaning to open the file in read mode. 182 183 .. note:: 184 185 Underlying encoded files are always opened in binary mode. 186 No automatic conversion of ``'\n'`` is done on reading and writing. 187 The *mode* argument may be any binary mode acceptable to the built-in 188 :func:`open` function; the ``'b'`` is automatically added. 189 190 *encoding* specifies the encoding which is to be used for the file. 191 Any encoding that encodes to and decodes from bytes is allowed, and 192 the data types supported by the file methods depend on the codec used. 193 194 *errors* may be given to define the error handling. It defaults to ``'strict'`` 195 which causes a :exc:`ValueError` to be raised in case an encoding error occurs. 196 197 *buffering* has the same meaning as for the built-in :func:`open` function. It 198 defaults to line buffered. 199 200 201.. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict') 202 203 Return a :class:`StreamRecoder` instance, a wrapped version of *file* 204 which provides transparent transcoding. The original file is closed 205 when the wrapped version is closed. 206 207 Data written to the wrapped file is decoded according to the given 208 *data_encoding* and then written to the original file as bytes using 209 *file_encoding*. Bytes read from the original file are decoded 210 according to *file_encoding*, and the result is encoded 211 using *data_encoding*. 212 213 If *file_encoding* is not given, it defaults to *data_encoding*. 214 215 *errors* may be given to define the error handling. It defaults to 216 ``'strict'``, which causes :exc:`ValueError` to be raised in case an encoding 217 error occurs. 218 219 220.. function:: iterencode(iterator, encoding, errors='strict', **kwargs) 221 222 Uses an incremental encoder to iteratively encode the input provided by 223 *iterator*. This function is a :term:`generator`. 224 The *errors* argument (as well as any 225 other keyword argument) is passed through to the incremental encoder. 226 227 This function requires that the codec accept text :class:`str` objects 228 to encode. Therefore it does not support bytes-to-bytes encoders such as 229 ``base64_codec``. 230 231 232.. function:: iterdecode(iterator, encoding, errors='strict', **kwargs) 233 234 Uses an incremental decoder to iteratively decode the input provided by 235 *iterator*. This function is a :term:`generator`. 236 The *errors* argument (as well as any 237 other keyword argument) is passed through to the incremental decoder. 238 239 This function requires that the codec accept :class:`bytes` objects 240 to decode. Therefore it does not support text-to-text encoders such as 241 ``rot_13``, although ``rot_13`` may be used equivalently with 242 :func:`iterencode`. 243 244 245The module also provides the following constants which are useful for reading 246and writing to platform dependent files: 247 248 249.. data:: BOM 250 BOM_BE 251 BOM_LE 252 BOM_UTF8 253 BOM_UTF16 254 BOM_UTF16_BE 255 BOM_UTF16_LE 256 BOM_UTF32 257 BOM_UTF32_BE 258 BOM_UTF32_LE 259 260 These constants define various byte sequences, 261 being Unicode byte order marks (BOMs) for several encodings. They are 262 used in UTF-16 and UTF-32 data streams to indicate the byte order used, 263 and in UTF-8 as a Unicode signature. :const:`BOM_UTF16` is either 264 :const:`BOM_UTF16_BE` or :const:`BOM_UTF16_LE` depending on the platform's 265 native byte order, :const:`BOM` is an alias for :const:`BOM_UTF16`, 266 :const:`BOM_LE` for :const:`BOM_UTF16_LE` and :const:`BOM_BE` for 267 :const:`BOM_UTF16_BE`. The others represent the BOM in UTF-8 and UTF-32 268 encodings. 269 270 271.. _codec-base-classes: 272 273Codec Base Classes 274------------------ 275 276The :mod:`codecs` module defines a set of base classes which define the 277interfaces for working with codec objects, and can also be used as the basis 278for custom codec implementations. 279 280Each codec has to define four interfaces to make it usable as codec in Python: 281stateless encoder, stateless decoder, stream reader and stream writer. The 282stream reader and writers typically reuse the stateless encoder/decoder to 283implement the file protocols. Codec authors also need to define how the 284codec will handle encoding and decoding errors. 285 286 287.. _surrogateescape: 288.. _error-handlers: 289 290Error Handlers 291^^^^^^^^^^^^^^ 292 293To simplify and standardize error handling, 294codecs may implement different error handling schemes by 295accepting the *errors* string argument. The following string values are 296defined and implemented by all standard Python codecs: 297 298.. tabularcolumns:: |l|L| 299 300+-------------------------+-----------------------------------------------+ 301| Value | Meaning | 302+=========================+===============================================+ 303| ``'strict'`` | Raise :exc:`UnicodeError` (or a subclass); | 304| | this is the default. Implemented in | 305| | :func:`strict_errors`. | 306+-------------------------+-----------------------------------------------+ 307| ``'ignore'`` | Ignore the malformed data and continue | 308| | without further notice. Implemented in | 309| | :func:`ignore_errors`. | 310+-------------------------+-----------------------------------------------+ 311 312The following error handlers are only applicable to 313:term:`text encodings <text encoding>`: 314 315+-------------------------+-----------------------------------------------+ 316| Value | Meaning | 317+=========================+===============================================+ 318| ``'replace'`` | Replace with a suitable replacement | 319| | marker; Python will use the official | 320| | ``U+FFFD`` REPLACEMENT CHARACTER for the | 321| | built-in codecs on decoding, and '?' on | 322| | encoding. Implemented in | 323| | :func:`replace_errors`. | 324+-------------------------+-----------------------------------------------+ 325| ``'xmlcharrefreplace'`` | Replace with the appropriate XML character | 326| | reference (only for encoding). Implemented | 327| | in :func:`xmlcharrefreplace_errors`. | 328+-------------------------+-----------------------------------------------+ 329| ``'backslashreplace'`` | Replace with backslashed escape sequences. | 330| | Implemented in | 331| | :func:`backslashreplace_errors`. | 332+-------------------------+-----------------------------------------------+ 333| ``'namereplace'`` | Replace with ``\N{...}`` escape sequences | 334| | (only for encoding). Implemented in | 335| | :func:`namereplace_errors`. | 336+-------------------------+-----------------------------------------------+ 337| ``'surrogateescape'`` | On decoding, replace byte with individual | 338| | surrogate code ranging from ``U+DC80`` to | 339| | ``U+DCFF``. This code will then be turned | 340| | back into the same byte when the | 341| | ``'surrogateescape'`` error handler is used | 342| | when encoding the data. (See :pep:`383` for | 343| | more.) | 344+-------------------------+-----------------------------------------------+ 345 346In addition, the following error handler is specific to the given codecs: 347 348+-------------------+------------------------+-------------------------------------------+ 349| Value | Codecs | Meaning | 350+===================+========================+===========================================+ 351|``'surrogatepass'``| utf-8, utf-16, utf-32, | Allow encoding and decoding of surrogate | 352| | utf-16-be, utf-16-le, | codes. These codecs normally treat the | 353| | utf-32-be, utf-32-le | presence of surrogates as an error. | 354+-------------------+------------------------+-------------------------------------------+ 355 356.. versionadded:: 3.1 357 The ``'surrogateescape'`` and ``'surrogatepass'`` error handlers. 358 359.. versionchanged:: 3.4 360 The ``'surrogatepass'`` error handlers now works with utf-16\* and utf-32\* codecs. 361 362.. versionadded:: 3.5 363 The ``'namereplace'`` error handler. 364 365.. versionchanged:: 3.5 366 The ``'backslashreplace'`` error handlers now works with decoding and 367 translating. 368 369The set of allowed values can be extended by registering a new named error 370handler: 371 372.. function:: register_error(name, error_handler) 373 374 Register the error handling function *error_handler* under the name *name*. 375 The *error_handler* argument will be called during encoding and decoding 376 in case of an error, when *name* is specified as the errors parameter. 377 378 For encoding, *error_handler* will be called with a :exc:`UnicodeEncodeError` 379 instance, which contains information about the location of the error. The 380 error handler must either raise this or a different exception, or return a 381 tuple with a replacement for the unencodable part of the input and a position 382 where encoding should continue. The replacement may be either :class:`str` or 383 :class:`bytes`. If the replacement is bytes, the encoder will simply copy 384 them into the output buffer. If the replacement is a string, the encoder will 385 encode the replacement. Encoding continues on original input at the 386 specified position. Negative position values will be treated as being 387 relative to the end of the input string. If the resulting position is out of 388 bound an :exc:`IndexError` will be raised. 389 390 Decoding and translating works similarly, except :exc:`UnicodeDecodeError` or 391 :exc:`UnicodeTranslateError` will be passed to the handler and that the 392 replacement from the error handler will be put into the output directly. 393 394 395Previously registered error handlers (including the standard error handlers) 396can be looked up by name: 397 398.. function:: lookup_error(name) 399 400 Return the error handler previously registered under the name *name*. 401 402 Raises a :exc:`LookupError` in case the handler cannot be found. 403 404The following standard error handlers are also made available as module level 405functions: 406 407.. function:: strict_errors(exception) 408 409 Implements the ``'strict'`` error handling: each encoding or 410 decoding error raises a :exc:`UnicodeError`. 411 412 413.. function:: replace_errors(exception) 414 415 Implements the ``'replace'`` error handling (for :term:`text encodings 416 <text encoding>` only): substitutes ``'?'`` for encoding errors 417 (to be encoded by the codec), and ``'\ufffd'`` (the Unicode replacement 418 character) for decoding errors. 419 420 421.. function:: ignore_errors(exception) 422 423 Implements the ``'ignore'`` error handling: malformed data is ignored and 424 encoding or decoding is continued without further notice. 425 426 427.. function:: xmlcharrefreplace_errors(exception) 428 429 Implements the ``'xmlcharrefreplace'`` error handling (for encoding with 430 :term:`text encodings <text encoding>` only): the 431 unencodable character is replaced by an appropriate XML character reference. 432 433 434.. function:: backslashreplace_errors(exception) 435 436 Implements the ``'backslashreplace'`` error handling (for 437 :term:`text encodings <text encoding>` only): malformed data is 438 replaced by a backslashed escape sequence. 439 440.. function:: namereplace_errors(exception) 441 442 Implements the ``'namereplace'`` error handling (for encoding with 443 :term:`text encodings <text encoding>` only): the 444 unencodable character is replaced by a ``\N{...}`` escape sequence. 445 446 .. versionadded:: 3.5 447 448 449.. _codec-objects: 450 451Stateless Encoding and Decoding 452^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 453 454The base :class:`Codec` class defines these methods which also define the 455function interfaces of the stateless encoder and decoder: 456 457 458.. method:: Codec.encode(input[, errors]) 459 460 Encodes the object *input* and returns a tuple (output object, length consumed). 461 For instance, :term:`text encoding` converts 462 a string object to a bytes object using a particular 463 character set encoding (e.g., ``cp1252`` or ``iso-8859-1``). 464 465 The *errors* argument defines the error handling to apply. 466 It defaults to ``'strict'`` handling. 467 468 The method may not store state in the :class:`Codec` instance. Use 469 :class:`StreamWriter` for codecs which have to keep state in order to make 470 encoding efficient. 471 472 The encoder must be able to handle zero length input and return an empty object 473 of the output object type in this situation. 474 475 476.. method:: Codec.decode(input[, errors]) 477 478 Decodes the object *input* and returns a tuple (output object, length 479 consumed). For instance, for a :term:`text encoding`, decoding converts 480 a bytes object encoded using a particular 481 character set encoding to a string object. 482 483 For text encodings and bytes-to-bytes codecs, 484 *input* must be a bytes object or one which provides the read-only 485 buffer interface -- for example, buffer objects and memory mapped files. 486 487 The *errors* argument defines the error handling to apply. 488 It defaults to ``'strict'`` handling. 489 490 The method may not store state in the :class:`Codec` instance. Use 491 :class:`StreamReader` for codecs which have to keep state in order to make 492 decoding efficient. 493 494 The decoder must be able to handle zero length input and return an empty object 495 of the output object type in this situation. 496 497 498Incremental Encoding and Decoding 499^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 500 501The :class:`IncrementalEncoder` and :class:`IncrementalDecoder` classes provide 502the basic interface for incremental encoding and decoding. Encoding/decoding the 503input isn't done with one call to the stateless encoder/decoder function, but 504with multiple calls to the 505:meth:`~IncrementalEncoder.encode`/:meth:`~IncrementalDecoder.decode` method of 506the incremental encoder/decoder. The incremental encoder/decoder keeps track of 507the encoding/decoding process during method calls. 508 509The joined output of calls to the 510:meth:`~IncrementalEncoder.encode`/:meth:`~IncrementalDecoder.decode` method is 511the same as if all the single inputs were joined into one, and this input was 512encoded/decoded with the stateless encoder/decoder. 513 514 515.. _incremental-encoder-objects: 516 517IncrementalEncoder Objects 518~~~~~~~~~~~~~~~~~~~~~~~~~~ 519 520The :class:`IncrementalEncoder` class is used for encoding an input in multiple 521steps. It defines the following methods which every incremental encoder must 522define in order to be compatible with the Python codec registry. 523 524 525.. class:: IncrementalEncoder(errors='strict') 526 527 Constructor for an :class:`IncrementalEncoder` instance. 528 529 All incremental encoders must provide this constructor interface. They are free 530 to add additional keyword arguments, but only the ones defined here are used by 531 the Python codec registry. 532 533 The :class:`IncrementalEncoder` may implement different error handling schemes 534 by providing the *errors* keyword argument. See :ref:`error-handlers` for 535 possible values. 536 537 The *errors* argument will be assigned to an attribute of the same name. 538 Assigning to this attribute makes it possible to switch between different error 539 handling strategies during the lifetime of the :class:`IncrementalEncoder` 540 object. 541 542 543 .. method:: encode(object[, final]) 544 545 Encodes *object* (taking the current state of the encoder into account) 546 and returns the resulting encoded object. If this is the last call to 547 :meth:`encode` *final* must be true (the default is false). 548 549 550 .. method:: reset() 551 552 Reset the encoder to the initial state. The output is discarded: call 553 ``.encode(object, final=True)``, passing an empty byte or text string 554 if necessary, to reset the encoder and to get the output. 555 556 557.. method:: IncrementalEncoder.getstate() 558 559 Return the current state of the encoder which must be an integer. The 560 implementation should make sure that ``0`` is the most common state. (States 561 that are more complicated than integers can be converted into an integer by 562 marshaling/pickling the state and encoding the bytes of the resulting string 563 into an integer). 564 565 566.. method:: IncrementalEncoder.setstate(state) 567 568 Set the state of the encoder to *state*. *state* must be an encoder state 569 returned by :meth:`getstate`. 570 571 572.. _incremental-decoder-objects: 573 574IncrementalDecoder Objects 575~~~~~~~~~~~~~~~~~~~~~~~~~~ 576 577The :class:`IncrementalDecoder` class is used for decoding an input in multiple 578steps. It defines the following methods which every incremental decoder must 579define in order to be compatible with the Python codec registry. 580 581 582.. class:: IncrementalDecoder(errors='strict') 583 584 Constructor for an :class:`IncrementalDecoder` instance. 585 586 All incremental decoders must provide this constructor interface. They are free 587 to add additional keyword arguments, but only the ones defined here are used by 588 the Python codec registry. 589 590 The :class:`IncrementalDecoder` may implement different error handling schemes 591 by providing the *errors* keyword argument. See :ref:`error-handlers` for 592 possible values. 593 594 The *errors* argument will be assigned to an attribute of the same name. 595 Assigning to this attribute makes it possible to switch between different error 596 handling strategies during the lifetime of the :class:`IncrementalDecoder` 597 object. 598 599 600 .. method:: decode(object[, final]) 601 602 Decodes *object* (taking the current state of the decoder into account) 603 and returns the resulting decoded object. If this is the last call to 604 :meth:`decode` *final* must be true (the default is false). If *final* is 605 true the decoder must decode the input completely and must flush all 606 buffers. If this isn't possible (e.g. because of incomplete byte sequences 607 at the end of the input) it must initiate error handling just like in the 608 stateless case (which might raise an exception). 609 610 611 .. method:: reset() 612 613 Reset the decoder to the initial state. 614 615 616 .. method:: getstate() 617 618 Return the current state of the decoder. This must be a tuple with two 619 items, the first must be the buffer containing the still undecoded 620 input. The second must be an integer and can be additional state 621 info. (The implementation should make sure that ``0`` is the most common 622 additional state info.) If this additional state info is ``0`` it must be 623 possible to set the decoder to the state which has no input buffered and 624 ``0`` as the additional state info, so that feeding the previously 625 buffered input to the decoder returns it to the previous state without 626 producing any output. (Additional state info that is more complicated than 627 integers can be converted into an integer by marshaling/pickling the info 628 and encoding the bytes of the resulting string into an integer.) 629 630 631 .. method:: setstate(state) 632 633 Set the state of the encoder to *state*. *state* must be a decoder state 634 returned by :meth:`getstate`. 635 636 637Stream Encoding and Decoding 638^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 639 640 641The :class:`StreamWriter` and :class:`StreamReader` classes provide generic 642working interfaces which can be used to implement new encoding submodules very 643easily. See :mod:`encodings.utf_8` for an example of how this is done. 644 645 646.. _stream-writer-objects: 647 648StreamWriter Objects 649~~~~~~~~~~~~~~~~~~~~ 650 651The :class:`StreamWriter` class is a subclass of :class:`Codec` and defines the 652following methods which every stream writer must define in order to be 653compatible with the Python codec registry. 654 655 656.. class:: StreamWriter(stream, errors='strict') 657 658 Constructor for a :class:`StreamWriter` instance. 659 660 All stream writers must provide this constructor interface. They are free to add 661 additional keyword arguments, but only the ones defined here are used by the 662 Python codec registry. 663 664 The *stream* argument must be a file-like object open for writing 665 text or binary data, as appropriate for the specific codec. 666 667 The :class:`StreamWriter` may implement different error handling schemes by 668 providing the *errors* keyword argument. See :ref:`error-handlers` for 669 the standard error handlers the underlying stream codec may support. 670 671 The *errors* argument will be assigned to an attribute of the same name. 672 Assigning to this attribute makes it possible to switch between different error 673 handling strategies during the lifetime of the :class:`StreamWriter` object. 674 675 .. method:: write(object) 676 677 Writes the object's contents encoded to the stream. 678 679 680 .. method:: writelines(list) 681 682 Writes the concatenated list of strings to the stream (possibly by reusing 683 the :meth:`write` method). The standard bytes-to-bytes codecs 684 do not support this method. 685 686 687 .. method:: reset() 688 689 Flushes and resets the codec buffers used for keeping state. 690 691 Calling this method should ensure that the data on the output is put into 692 a clean state that allows appending of new fresh data without having to 693 rescan the whole stream to recover state. 694 695 696In addition to the above methods, the :class:`StreamWriter` must also inherit 697all other methods and attributes from the underlying stream. 698 699 700.. _stream-reader-objects: 701 702StreamReader Objects 703~~~~~~~~~~~~~~~~~~~~ 704 705The :class:`StreamReader` class is a subclass of :class:`Codec` and defines the 706following methods which every stream reader must define in order to be 707compatible with the Python codec registry. 708 709 710.. class:: StreamReader(stream, errors='strict') 711 712 Constructor for a :class:`StreamReader` instance. 713 714 All stream readers must provide this constructor interface. They are free to add 715 additional keyword arguments, but only the ones defined here are used by the 716 Python codec registry. 717 718 The *stream* argument must be a file-like object open for reading 719 text or binary data, as appropriate for the specific codec. 720 721 The :class:`StreamReader` may implement different error handling schemes by 722 providing the *errors* keyword argument. See :ref:`error-handlers` for 723 the standard error handlers the underlying stream codec may support. 724 725 The *errors* argument will be assigned to an attribute of the same name. 726 Assigning to this attribute makes it possible to switch between different error 727 handling strategies during the lifetime of the :class:`StreamReader` object. 728 729 The set of allowed values for the *errors* argument can be extended with 730 :func:`register_error`. 731 732 733 .. method:: read([size[, chars, [firstline]]]) 734 735 Decodes data from the stream and returns the resulting object. 736 737 The *chars* argument indicates the number of decoded 738 code points or bytes to return. The :func:`read` method will 739 never return more data than requested, but it might return less, 740 if there is not enough available. 741 742 The *size* argument indicates the approximate maximum 743 number of encoded bytes or code points to read 744 for decoding. The decoder can modify this setting as 745 appropriate. The default value -1 indicates to read and decode as much as 746 possible. This parameter is intended to 747 prevent having to decode huge files in one step. 748 749 The *firstline* flag indicates that 750 it would be sufficient to only return the first 751 line, if there are decoding errors on later lines. 752 753 The method should use a greedy read strategy meaning that it should read 754 as much data as is allowed within the definition of the encoding and the 755 given size, e.g. if optional encoding endings or state markers are 756 available on the stream, these should be read too. 757 758 759 .. method:: readline([size[, keepends]]) 760 761 Read one line from the input stream and return the decoded data. 762 763 *size*, if given, is passed as size argument to the stream's 764 :meth:`read` method. 765 766 If *keepends* is false line-endings will be stripped from the lines 767 returned. 768 769 770 .. method:: readlines([sizehint[, keepends]]) 771 772 Read all lines available on the input stream and return them as a list of 773 lines. 774 775 Line-endings are implemented using the codec's decoder method and are 776 included in the list entries if *keepends* is true. 777 778 *sizehint*, if given, is passed as the *size* argument to the stream's 779 :meth:`read` method. 780 781 782 .. method:: reset() 783 784 Resets the codec buffers used for keeping state. 785 786 Note that no stream repositioning should take place. This method is 787 primarily intended to be able to recover from decoding errors. 788 789 790In addition to the above methods, the :class:`StreamReader` must also inherit 791all other methods and attributes from the underlying stream. 792 793.. _stream-reader-writer: 794 795StreamReaderWriter Objects 796~~~~~~~~~~~~~~~~~~~~~~~~~~ 797 798The :class:`StreamReaderWriter` is a convenience class that allows wrapping 799streams which work in both read and write modes. 800 801The design is such that one can use the factory functions returned by the 802:func:`lookup` function to construct the instance. 803 804 805.. class:: StreamReaderWriter(stream, Reader, Writer, errors) 806 807 Creates a :class:`StreamReaderWriter` instance. *stream* must be a file-like 808 object. *Reader* and *Writer* must be factory functions or classes providing the 809 :class:`StreamReader` and :class:`StreamWriter` interface resp. Error handling 810 is done in the same way as defined for the stream readers and writers. 811 812:class:`StreamReaderWriter` instances define the combined interfaces of 813:class:`StreamReader` and :class:`StreamWriter` classes. They inherit all other 814methods and attributes from the underlying stream. 815 816 817.. _stream-recoder-objects: 818 819StreamRecoder Objects 820~~~~~~~~~~~~~~~~~~~~~ 821 822The :class:`StreamRecoder` translates data from one encoding to another, 823which is sometimes useful when dealing with different encoding environments. 824 825The design is such that one can use the factory functions returned by the 826:func:`lookup` function to construct the instance. 827 828 829.. class:: StreamRecoder(stream, encode, decode, Reader, Writer, errors) 830 831 Creates a :class:`StreamRecoder` instance which implements a two-way conversion: 832 *encode* and *decode* work on the frontend — the data visible to 833 code calling :meth:`read` and :meth:`write`, while *Reader* and *Writer* 834 work on the backend — the data in *stream*. 835 836 You can use these objects to do transparent transcodings from e.g. Latin-1 837 to UTF-8 and back. 838 839 The *stream* argument must be a file-like object. 840 841 The *encode* and *decode* arguments must 842 adhere to the :class:`Codec` interface. *Reader* and 843 *Writer* must be factory functions or classes providing objects of the 844 :class:`StreamReader` and :class:`StreamWriter` interface respectively. 845 846 Error handling is done in the same way as defined for the stream readers and 847 writers. 848 849 850:class:`StreamRecoder` instances define the combined interfaces of 851:class:`StreamReader` and :class:`StreamWriter` classes. They inherit all other 852methods and attributes from the underlying stream. 853 854 855.. _encodings-overview: 856 857Encodings and Unicode 858--------------------- 859 860Strings are stored internally as sequences of code points in 861range ``0x0``--``0x10FFFF``. (See :pep:`393` for 862more details about the implementation.) 863Once a string object is used outside of CPU and memory, endianness 864and how these arrays are stored as bytes become an issue. As with other 865codecs, serialising a string into a sequence of bytes is known as *encoding*, 866and recreating the string from the sequence of bytes is known as *decoding*. 867There are a variety of different text serialisation codecs, which are 868collectivity referred to as :term:`text encodings <text encoding>`. 869 870The simplest text encoding (called ``'latin-1'`` or ``'iso-8859-1'``) maps 871the code points 0--255 to the bytes ``0x0``--``0xff``, which means that a string 872object that contains code points above ``U+00FF`` can't be encoded with this 873codec. Doing so will raise a :exc:`UnicodeEncodeError` that looks 874like the following (although the details of the error message may differ): 875``UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in 876position 3: ordinal not in range(256)``. 877 878There's another group of encodings (the so called charmap encodings) that choose 879a different subset of all Unicode code points and how these code points are 880mapped to the bytes ``0x0``--``0xff``. To see how this is done simply open 881e.g. :file:`encodings/cp1252.py` (which is an encoding that is used primarily on 882Windows). There's a string constant with 256 characters that shows you which 883character is mapped to which byte value. 884 885All of these encodings can only encode 256 of the 1114112 code points 886defined in Unicode. A simple and straightforward way that can store each Unicode 887code point, is to store each code point as four consecutive bytes. There are two 888possibilities: store the bytes in big endian or in little endian order. These 889two encodings are called ``UTF-32-BE`` and ``UTF-32-LE`` respectively. Their 890disadvantage is that if e.g. you use ``UTF-32-BE`` on a little endian machine you 891will always have to swap bytes on encoding and decoding. ``UTF-32`` avoids this 892problem: bytes will always be in natural endianness. When these bytes are read 893by a CPU with a different endianness, then bytes have to be swapped though. To 894be able to detect the endianness of a ``UTF-16`` or ``UTF-32`` byte sequence, 895there's the so called BOM ("Byte Order Mark"). This is the Unicode character 896``U+FEFF``. This character can be prepended to every ``UTF-16`` or ``UTF-32`` 897byte sequence. The byte swapped version of this character (``0xFFFE``) is an 898illegal character that may not appear in a Unicode text. So when the 899first character in an ``UTF-16`` or ``UTF-32`` byte sequence 900appears to be a ``U+FFFE`` the bytes have to be swapped on decoding. 901Unfortunately the character ``U+FEFF`` had a second purpose as 902a ``ZERO WIDTH NO-BREAK SPACE``: a character that has no width and doesn't allow 903a word to be split. It can e.g. be used to give hints to a ligature algorithm. 904With Unicode 4.0 using ``U+FEFF`` as a ``ZERO WIDTH NO-BREAK SPACE`` has been 905deprecated (with ``U+2060`` (``WORD JOINER``) assuming this role). Nevertheless 906Unicode software still must be able to handle ``U+FEFF`` in both roles: as a BOM 907it's a device to determine the storage layout of the encoded bytes, and vanishes 908once the byte sequence has been decoded into a string; as a ``ZERO WIDTH 909NO-BREAK SPACE`` it's a normal character that will be decoded like any other. 910 911There's another encoding that is able to encoding the full range of Unicode 912characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues 913with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two 914parts: marker bits (the most significant bits) and payload bits. The marker bits 915are a sequence of zero to four ``1`` bits followed by a ``0`` bit. Unicode characters are 916encoded like this (with x being payload bits, which when concatenated give the 917Unicode character): 918 919+-----------------------------------+----------------------------------------------+ 920| Range | Encoding | 921+===================================+==============================================+ 922| ``U-00000000`` ... ``U-0000007F`` | 0xxxxxxx | 923+-----------------------------------+----------------------------------------------+ 924| ``U-00000080`` ... ``U-000007FF`` | 110xxxxx 10xxxxxx | 925+-----------------------------------+----------------------------------------------+ 926| ``U-00000800`` ... ``U-0000FFFF`` | 1110xxxx 10xxxxxx 10xxxxxx | 927+-----------------------------------+----------------------------------------------+ 928| ``U-00010000`` ... ``U-0010FFFF`` | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx | 929+-----------------------------------+----------------------------------------------+ 930 931The least significant bit of the Unicode character is the rightmost x bit. 932 933As UTF-8 is an 8-bit encoding no BOM is required and any ``U+FEFF`` character in 934the decoded string (even if it's the first character) is treated as a ``ZERO 935WIDTH NO-BREAK SPACE``. 936 937Without external information it's impossible to reliably determine which 938encoding was used for encoding a string. Each charmap encoding can 939decode any random byte sequence. However that's not possible with UTF-8, as 940UTF-8 byte sequences have a structure that doesn't allow arbitrary byte 941sequences. To increase the reliability with which a UTF-8 encoding can be 942detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls 943``"utf-8-sig"``) for its Notepad program: Before any of the Unicode characters 944is written to the file, a UTF-8 encoded BOM (which looks like this as a byte 945sequence: ``0xef``, ``0xbb``, ``0xbf``) is written. As it's rather improbable 946that any charmap encoded file starts with these byte values (which would e.g. 947map to 948 949 | LATIN SMALL LETTER I WITH DIAERESIS 950 | RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK 951 | INVERTED QUESTION MARK 952 953in iso-8859-1), this increases the probability that a ``utf-8-sig`` encoding can be 954correctly guessed from the byte sequence. So here the BOM is not used to be able 955to determine the byte order used for generating the byte sequence, but as a 956signature that helps in guessing the encoding. On encoding the utf-8-sig codec 957will write ``0xef``, ``0xbb``, ``0xbf`` as the first three bytes to the file. On 958decoding ``utf-8-sig`` will skip those three bytes if they appear as the first 959three bytes in the file. In UTF-8, the use of the BOM is discouraged and 960should generally be avoided. 961 962 963.. _standard-encodings: 964 965Standard Encodings 966------------------ 967 968Python comes with a number of codecs built-in, either implemented as C functions 969or with dictionaries as mapping tables. The following table lists the codecs by 970name, together with a few common aliases, and the languages for which the 971encoding is likely used. Neither the list of aliases nor the list of languages 972is meant to be exhaustive. Notice that spelling alternatives that only differ in 973case or use a hyphen instead of an underscore are also valid aliases; therefore, 974e.g. ``'utf-8'`` is a valid alias for the ``'utf_8'`` codec. 975 976.. impl-detail:: 977 978 Some common encodings can bypass the codecs lookup machinery to 979 improve performance. These optimization opportunities are only 980 recognized by CPython for a limited set of aliases: utf-8, utf8, 981 latin-1, latin1, iso-8859-1, mbcs (Windows only), ascii, utf-16, 982 and utf-32. Using alternative spellings for these encodings may 983 result in slower execution. 984 985Many of the character sets support the same languages. They vary in individual 986characters (e.g. whether the EURO SIGN is supported or not), and in the 987assignment of characters to code positions. For the European languages in 988particular, the following variants typically exist: 989 990* an ISO 8859 codeset 991 992* a Microsoft Windows code page, which is typically derived from an 8859 codeset, 993 but replaces control characters with additional graphic characters 994 995* an IBM EBCDIC code page 996 997* an IBM PC code page, which is ASCII compatible 998 999.. tabularcolumns:: |l|p{0.3\linewidth}|p{0.3\linewidth}| 1000 1001+-----------------+--------------------------------+--------------------------------+ 1002| Codec | Aliases | Languages | 1003+=================+================================+================================+ 1004| ascii | 646, us-ascii | English | 1005+-----------------+--------------------------------+--------------------------------+ 1006| big5 | big5-tw, csbig5 | Traditional Chinese | 1007+-----------------+--------------------------------+--------------------------------+ 1008| big5hkscs | big5-hkscs, hkscs | Traditional Chinese | 1009+-----------------+--------------------------------+--------------------------------+ 1010| cp037 | IBM037, IBM039 | English | 1011+-----------------+--------------------------------+--------------------------------+ 1012| cp273 | 273, IBM273, csIBM273 | German | 1013| | | | 1014| | | .. versionadded:: 3.4 | 1015+-----------------+--------------------------------+--------------------------------+ 1016| cp424 | EBCDIC-CP-HE, IBM424 | Hebrew | 1017+-----------------+--------------------------------+--------------------------------+ 1018| cp437 | 437, IBM437 | English | 1019+-----------------+--------------------------------+--------------------------------+ 1020| cp500 | EBCDIC-CP-BE, EBCDIC-CP-CH, | Western Europe | 1021| | IBM500 | | 1022+-----------------+--------------------------------+--------------------------------+ 1023| cp720 | | Arabic | 1024+-----------------+--------------------------------+--------------------------------+ 1025| cp737 | | Greek | 1026+-----------------+--------------------------------+--------------------------------+ 1027| cp775 | IBM775 | Baltic languages | 1028+-----------------+--------------------------------+--------------------------------+ 1029| cp850 | 850, IBM850 | Western Europe | 1030+-----------------+--------------------------------+--------------------------------+ 1031| cp852 | 852, IBM852 | Central and Eastern Europe | 1032+-----------------+--------------------------------+--------------------------------+ 1033| cp855 | 855, IBM855 | Bulgarian, Byelorussian, | 1034| | | Macedonian, Russian, Serbian | 1035+-----------------+--------------------------------+--------------------------------+ 1036| cp856 | | Hebrew | 1037+-----------------+--------------------------------+--------------------------------+ 1038| cp857 | 857, IBM857 | Turkish | 1039+-----------------+--------------------------------+--------------------------------+ 1040| cp858 | 858, IBM858 | Western Europe | 1041+-----------------+--------------------------------+--------------------------------+ 1042| cp860 | 860, IBM860 | Portuguese | 1043+-----------------+--------------------------------+--------------------------------+ 1044| cp861 | 861, CP-IS, IBM861 | Icelandic | 1045+-----------------+--------------------------------+--------------------------------+ 1046| cp862 | 862, IBM862 | Hebrew | 1047+-----------------+--------------------------------+--------------------------------+ 1048| cp863 | 863, IBM863 | Canadian | 1049+-----------------+--------------------------------+--------------------------------+ 1050| cp864 | IBM864 | Arabic | 1051+-----------------+--------------------------------+--------------------------------+ 1052| cp865 | 865, IBM865 | Danish, Norwegian | 1053+-----------------+--------------------------------+--------------------------------+ 1054| cp866 | 866, IBM866 | Russian | 1055+-----------------+--------------------------------+--------------------------------+ 1056| cp869 | 869, CP-GR, IBM869 | Greek | 1057+-----------------+--------------------------------+--------------------------------+ 1058| cp874 | | Thai | 1059+-----------------+--------------------------------+--------------------------------+ 1060| cp875 | | Greek | 1061+-----------------+--------------------------------+--------------------------------+ 1062| cp932 | 932, ms932, mskanji, ms-kanji | Japanese | 1063+-----------------+--------------------------------+--------------------------------+ 1064| cp949 | 949, ms949, uhc | Korean | 1065+-----------------+--------------------------------+--------------------------------+ 1066| cp950 | 950, ms950 | Traditional Chinese | 1067+-----------------+--------------------------------+--------------------------------+ 1068| cp1006 | | Urdu | 1069+-----------------+--------------------------------+--------------------------------+ 1070| cp1026 | ibm1026 | Turkish | 1071+-----------------+--------------------------------+--------------------------------+ 1072| cp1125 | 1125, ibm1125, cp866u, ruscii | Ukrainian | 1073| | | | 1074| | | .. versionadded:: 3.4 | 1075+-----------------+--------------------------------+--------------------------------+ 1076| cp1140 | ibm1140 | Western Europe | 1077+-----------------+--------------------------------+--------------------------------+ 1078| cp1250 | windows-1250 | Central and Eastern Europe | 1079+-----------------+--------------------------------+--------------------------------+ 1080| cp1251 | windows-1251 | Bulgarian, Byelorussian, | 1081| | | Macedonian, Russian, Serbian | 1082+-----------------+--------------------------------+--------------------------------+ 1083| cp1252 | windows-1252 | Western Europe | 1084+-----------------+--------------------------------+--------------------------------+ 1085| cp1253 | windows-1253 | Greek | 1086+-----------------+--------------------------------+--------------------------------+ 1087| cp1254 | windows-1254 | Turkish | 1088+-----------------+--------------------------------+--------------------------------+ 1089| cp1255 | windows-1255 | Hebrew | 1090+-----------------+--------------------------------+--------------------------------+ 1091| cp1256 | windows-1256 | Arabic | 1092+-----------------+--------------------------------+--------------------------------+ 1093| cp1257 | windows-1257 | Baltic languages | 1094+-----------------+--------------------------------+--------------------------------+ 1095| cp1258 | windows-1258 | Vietnamese | 1096+-----------------+--------------------------------+--------------------------------+ 1097| cp65001 | | Windows only: Windows UTF-8 | 1098| | | (``CP_UTF8``) | 1099| | | | 1100| | | .. versionadded:: 3.3 | 1101+-----------------+--------------------------------+--------------------------------+ 1102| euc_jp | eucjp, ujis, u-jis | Japanese | 1103+-----------------+--------------------------------+--------------------------------+ 1104| euc_jis_2004 | jisx0213, eucjis2004 | Japanese | 1105+-----------------+--------------------------------+--------------------------------+ 1106| euc_jisx0213 | eucjisx0213 | Japanese | 1107+-----------------+--------------------------------+--------------------------------+ 1108| euc_kr | euckr, korean, ksc5601, | Korean | 1109| | ks_c-5601, ks_c-5601-1987, | | 1110| | ksx1001, ks_x-1001 | | 1111+-----------------+--------------------------------+--------------------------------+ 1112| gb2312 | chinese, csiso58gb231280, euc- | Simplified Chinese | 1113| | cn, euccn, eucgb2312-cn, | | 1114| | gb2312-1980, gb2312-80, iso- | | 1115| | ir-58 | | 1116+-----------------+--------------------------------+--------------------------------+ 1117| gbk | 936, cp936, ms936 | Unified Chinese | 1118+-----------------+--------------------------------+--------------------------------+ 1119| gb18030 | gb18030-2000 | Unified Chinese | 1120+-----------------+--------------------------------+--------------------------------+ 1121| hz | hzgb, hz-gb, hz-gb-2312 | Simplified Chinese | 1122+-----------------+--------------------------------+--------------------------------+ 1123| iso2022_jp | csiso2022jp, iso2022jp, | Japanese | 1124| | iso-2022-jp | | 1125+-----------------+--------------------------------+--------------------------------+ 1126| iso2022_jp_1 | iso2022jp-1, iso-2022-jp-1 | Japanese | 1127+-----------------+--------------------------------+--------------------------------+ 1128| iso2022_jp_2 | iso2022jp-2, iso-2022-jp-2 | Japanese, Korean, Simplified | 1129| | | Chinese, Western Europe, Greek | 1130+-----------------+--------------------------------+--------------------------------+ 1131| iso2022_jp_2004 | iso2022jp-2004, | Japanese | 1132| | iso-2022-jp-2004 | | 1133+-----------------+--------------------------------+--------------------------------+ 1134| iso2022_jp_3 | iso2022jp-3, iso-2022-jp-3 | Japanese | 1135+-----------------+--------------------------------+--------------------------------+ 1136| iso2022_jp_ext | iso2022jp-ext, iso-2022-jp-ext | Japanese | 1137+-----------------+--------------------------------+--------------------------------+ 1138| iso2022_kr | csiso2022kr, iso2022kr, | Korean | 1139| | iso-2022-kr | | 1140+-----------------+--------------------------------+--------------------------------+ 1141| latin_1 | iso-8859-1, iso8859-1, 8859, | West Europe | 1142| | cp819, latin, latin1, L1 | | 1143+-----------------+--------------------------------+--------------------------------+ 1144| iso8859_2 | iso-8859-2, latin2, L2 | Central and Eastern Europe | 1145+-----------------+--------------------------------+--------------------------------+ 1146| iso8859_3 | iso-8859-3, latin3, L3 | Esperanto, Maltese | 1147+-----------------+--------------------------------+--------------------------------+ 1148| iso8859_4 | iso-8859-4, latin4, L4 | Baltic languages | 1149+-----------------+--------------------------------+--------------------------------+ 1150| iso8859_5 | iso-8859-5, cyrillic | Bulgarian, Byelorussian, | 1151| | | Macedonian, Russian, Serbian | 1152+-----------------+--------------------------------+--------------------------------+ 1153| iso8859_6 | iso-8859-6, arabic | Arabic | 1154+-----------------+--------------------------------+--------------------------------+ 1155| iso8859_7 | iso-8859-7, greek, greek8 | Greek | 1156+-----------------+--------------------------------+--------------------------------+ 1157| iso8859_8 | iso-8859-8, hebrew | Hebrew | 1158+-----------------+--------------------------------+--------------------------------+ 1159| iso8859_9 | iso-8859-9, latin5, L5 | Turkish | 1160+-----------------+--------------------------------+--------------------------------+ 1161| iso8859_10 | iso-8859-10, latin6, L6 | Nordic languages | 1162+-----------------+--------------------------------+--------------------------------+ 1163| iso8859_11 | iso-8859-11, thai | Thai languages | 1164+-----------------+--------------------------------+--------------------------------+ 1165| iso8859_13 | iso-8859-13, latin7, L7 | Baltic languages | 1166+-----------------+--------------------------------+--------------------------------+ 1167| iso8859_14 | iso-8859-14, latin8, L8 | Celtic languages | 1168+-----------------+--------------------------------+--------------------------------+ 1169| iso8859_15 | iso-8859-15, latin9, L9 | Western Europe | 1170+-----------------+--------------------------------+--------------------------------+ 1171| iso8859_16 | iso-8859-16, latin10, L10 | South-Eastern Europe | 1172+-----------------+--------------------------------+--------------------------------+ 1173| johab | cp1361, ms1361 | Korean | 1174+-----------------+--------------------------------+--------------------------------+ 1175| koi8_r | | Russian | 1176+-----------------+--------------------------------+--------------------------------+ 1177| koi8_t | | Tajik | 1178| | | | 1179| | | .. versionadded:: 3.5 | 1180+-----------------+--------------------------------+--------------------------------+ 1181| koi8_u | | Ukrainian | 1182+-----------------+--------------------------------+--------------------------------+ 1183| kz1048 | kz_1048, strk1048_2002, rk1048 | Kazakh | 1184| | | | 1185| | | .. versionadded:: 3.5 | 1186+-----------------+--------------------------------+--------------------------------+ 1187| mac_cyrillic | maccyrillic | Bulgarian, Byelorussian, | 1188| | | Macedonian, Russian, Serbian | 1189+-----------------+--------------------------------+--------------------------------+ 1190| mac_greek | macgreek | Greek | 1191+-----------------+--------------------------------+--------------------------------+ 1192| mac_iceland | maciceland | Icelandic | 1193+-----------------+--------------------------------+--------------------------------+ 1194| mac_latin2 | maclatin2, maccentraleurope | Central and Eastern Europe | 1195+-----------------+--------------------------------+--------------------------------+ 1196| mac_roman | macroman, macintosh | Western Europe | 1197+-----------------+--------------------------------+--------------------------------+ 1198| mac_turkish | macturkish | Turkish | 1199+-----------------+--------------------------------+--------------------------------+ 1200| ptcp154 | csptcp154, pt154, cp154, | Kazakh | 1201| | cyrillic-asian | | 1202+-----------------+--------------------------------+--------------------------------+ 1203| shift_jis | csshiftjis, shiftjis, sjis, | Japanese | 1204| | s_jis | | 1205+-----------------+--------------------------------+--------------------------------+ 1206| shift_jis_2004 | shiftjis2004, sjis_2004, | Japanese | 1207| | sjis2004 | | 1208+-----------------+--------------------------------+--------------------------------+ 1209| shift_jisx0213 | shiftjisx0213, sjisx0213, | Japanese | 1210| | s_jisx0213 | | 1211+-----------------+--------------------------------+--------------------------------+ 1212| utf_32 | U32, utf32 | all languages | 1213+-----------------+--------------------------------+--------------------------------+ 1214| utf_32_be | UTF-32BE | all languages | 1215+-----------------+--------------------------------+--------------------------------+ 1216| utf_32_le | UTF-32LE | all languages | 1217+-----------------+--------------------------------+--------------------------------+ 1218| utf_16 | U16, utf16 | all languages | 1219+-----------------+--------------------------------+--------------------------------+ 1220| utf_16_be | UTF-16BE | all languages | 1221+-----------------+--------------------------------+--------------------------------+ 1222| utf_16_le | UTF-16LE | all languages | 1223+-----------------+--------------------------------+--------------------------------+ 1224| utf_7 | U7, unicode-1-1-utf-7 | all languages | 1225+-----------------+--------------------------------+--------------------------------+ 1226| utf_8 | U8, UTF, utf8 | all languages | 1227+-----------------+--------------------------------+--------------------------------+ 1228| utf_8_sig | | all languages | 1229+-----------------+--------------------------------+--------------------------------+ 1230 1231.. versionchanged:: 3.4 1232 The utf-16\* and utf-32\* encoders no longer allow surrogate code points 1233 (``U+D800``--``U+DFFF``) to be encoded. 1234 The utf-32\* decoders no longer decode 1235 byte sequences that correspond to surrogate code points. 1236 1237 1238Python Specific Encodings 1239------------------------- 1240 1241A number of predefined codecs are specific to Python, so their codec names have 1242no meaning outside Python. These are listed in the tables below based on the 1243expected input and output types (note that while text encodings are the most 1244common use case for codecs, the underlying codec infrastructure supports 1245arbitrary data transforms rather than just text encodings). For asymmetric 1246codecs, the stated purpose describes the encoding direction. 1247 1248Text Encodings 1249^^^^^^^^^^^^^^ 1250 1251The following codecs provide :class:`str` to :class:`bytes` encoding and 1252:term:`bytes-like object` to :class:`str` decoding, similar to the Unicode text 1253encodings. 1254 1255.. tabularcolumns:: |l|p{0.3\linewidth}|p{0.3\linewidth}| 1256 1257+--------------------+---------+---------------------------+ 1258| Codec | Aliases | Purpose | 1259+====================+=========+===========================+ 1260| idna | | Implements :rfc:`3490`, | 1261| | | see also | 1262| | | :mod:`encodings.idna`. | 1263| | | Only ``errors='strict'`` | 1264| | | is supported. | 1265+--------------------+---------+---------------------------+ 1266| mbcs | ansi, | Windows only: Encode | 1267| | dbcs | operand according to the | 1268| | | ANSI codepage (CP_ACP) | 1269+--------------------+---------+---------------------------+ 1270| oem | | Windows only: Encode | 1271| | | operand according to the | 1272| | | OEM codepage (CP_OEMCP) | 1273| | | | 1274| | | .. versionadded:: 3.6 | 1275+--------------------+---------+---------------------------+ 1276| palmos | | Encoding of PalmOS 3.5 | 1277+--------------------+---------+---------------------------+ 1278| punycode | | Implements :rfc:`3492`. | 1279| | | Stateful codecs are not | 1280| | | supported. | 1281+--------------------+---------+---------------------------+ 1282| raw_unicode_escape | | Latin-1 encoding with | 1283| | | ``\uXXXX`` and | 1284| | | ``\UXXXXXXXX`` for other | 1285| | | code points. Existing | 1286| | | backslashes are not | 1287| | | escaped in any way. | 1288| | | It is used in the Python | 1289| | | pickle protocol. | 1290+--------------------+---------+---------------------------+ 1291| undefined | | Raise an exception for | 1292| | | all conversions, even | 1293| | | empty strings. The error | 1294| | | handler is ignored. | 1295+--------------------+---------+---------------------------+ 1296| unicode_escape | | Encoding suitable as the | 1297| | | contents of a Unicode | 1298| | | literal in ASCII-encoded | 1299| | | Python source code, | 1300| | | except that quotes are | 1301| | | not escaped. Decodes from | 1302| | | Latin-1 source code. | 1303| | | Beware that Python source | 1304| | | code actually uses UTF-8 | 1305| | | by default. | 1306+--------------------+---------+---------------------------+ 1307| unicode_internal | | Return the internal | 1308| | | representation of the | 1309| | | operand. Stateful codecs | 1310| | | are not supported. | 1311| | | | 1312| | | .. deprecated:: 3.3 | 1313| | | This representation is | 1314| | | obsoleted by | 1315| | | :pep:`393`. | 1316+--------------------+---------+---------------------------+ 1317 1318.. _binary-transforms: 1319 1320Binary Transforms 1321^^^^^^^^^^^^^^^^^ 1322 1323The following codecs provide binary transforms: :term:`bytes-like object` 1324to :class:`bytes` mappings. They are not supported by :meth:`bytes.decode` 1325(which only produces :class:`str` output). 1326 1327 1328.. tabularcolumns:: |l|L|L|L| 1329 1330+----------------------+------------------+------------------------------+------------------------------+ 1331| Codec | Aliases | Purpose | Encoder / decoder | 1332+======================+==================+==============================+==============================+ 1333| base64_codec [#b64]_ | base64, base_64 | Convert operand to multiline | :meth:`base64.encodebytes` / | 1334| | | MIME base64 (the result | :meth:`base64.decodebytes` | 1335| | | always includes a trailing | | 1336| | | ``'\n'``) | | 1337| | | | | 1338| | | .. versionchanged:: 3.4 | | 1339| | | accepts any | | 1340| | | :term:`bytes-like object` | | 1341| | | as input for encoding and | | 1342| | | decoding | | 1343+----------------------+------------------+------------------------------+------------------------------+ 1344| bz2_codec | bz2 | Compress the operand | :meth:`bz2.compress` / | 1345| | | using bz2 | :meth:`bz2.decompress` | 1346+----------------------+------------------+------------------------------+------------------------------+ 1347| hex_codec | hex | Convert operand to | :meth:`binascii.b2a_hex` / | 1348| | | hexadecimal | :meth:`binascii.a2b_hex` | 1349| | | representation, with two | | 1350| | | digits per byte | | 1351+----------------------+------------------+------------------------------+------------------------------+ 1352| quopri_codec | quopri, | Convert operand to MIME | :meth:`quopri.encode` with | 1353| | quotedprintable, | quoted printable | ``quotetabs=True`` / | 1354| | quoted_printable | | :meth:`quopri.decode` | 1355+----------------------+------------------+------------------------------+------------------------------+ 1356| uu_codec | uu | Convert the operand using | :meth:`uu.encode` / | 1357| | | uuencode | :meth:`uu.decode` | 1358+----------------------+------------------+------------------------------+------------------------------+ 1359| zlib_codec | zip, zlib | Compress the operand | :meth:`zlib.compress` / | 1360| | | using gzip | :meth:`zlib.decompress` | 1361+----------------------+------------------+------------------------------+------------------------------+ 1362 1363.. [#b64] In addition to :term:`bytes-like objects <bytes-like object>`, 1364 ``'base64_codec'`` also accepts ASCII-only instances of :class:`str` for 1365 decoding 1366 1367.. versionadded:: 3.2 1368 Restoration of the binary transforms. 1369 1370.. versionchanged:: 3.4 1371 Restoration of the aliases for the binary transforms. 1372 1373 1374.. _text-transforms: 1375 1376Text Transforms 1377^^^^^^^^^^^^^^^ 1378 1379The following codec provides a text transform: a :class:`str` to :class:`str` 1380mapping. It is not supported by :meth:`str.encode` (which only produces 1381:class:`bytes` output). 1382 1383.. tabularcolumns:: |l|l|L| 1384 1385+--------------------+---------+---------------------------+ 1386| Codec | Aliases | Purpose | 1387+====================+=========+===========================+ 1388| rot_13 | rot13 | Returns the Caesar-cypher | 1389| | | encryption of the operand | 1390+--------------------+---------+---------------------------+ 1391 1392.. versionadded:: 3.2 1393 Restoration of the ``rot_13`` text transform. 1394 1395.. versionchanged:: 3.4 1396 Restoration of the ``rot13`` alias. 1397 1398 1399:mod:`encodings.idna` --- Internationalized Domain Names in Applications 1400------------------------------------------------------------------------ 1401 1402.. module:: encodings.idna 1403 :synopsis: Internationalized Domain Names implementation 1404.. moduleauthor:: Martin v. Löwis 1405 1406This module implements :rfc:`3490` (Internationalized Domain Names in 1407Applications) and :rfc:`3492` (Nameprep: A Stringprep Profile for 1408Internationalized Domain Names (IDN)). It builds upon the ``punycode`` encoding 1409and :mod:`stringprep`. 1410 1411These RFCs together define a protocol to support non-ASCII characters in domain 1412names. A domain name containing non-ASCII characters (such as 1413``www.Alliancefrançaise.nu``) is converted into an ASCII-compatible encoding 1414(ACE, such as ``www.xn--alliancefranaise-npb.nu``). The ACE form of the domain 1415name is then used in all places where arbitrary characters are not allowed by 1416the protocol, such as DNS queries, HTTP :mailheader:`Host` fields, and so 1417on. This conversion is carried out in the application; if possible invisible to 1418the user: The application should transparently convert Unicode domain labels to 1419IDNA on the wire, and convert back ACE labels to Unicode before presenting them 1420to the user. 1421 1422Python supports this conversion in several ways: the ``idna`` codec performs 1423conversion between Unicode and ACE, separating an input string into labels 1424based on the separator characters defined in `section 3.1`_ (1) of :rfc:`3490` 1425and converting each label to ACE as required, and conversely separating an input 1426byte string into labels based on the ``.`` separator and converting any ACE 1427labels found into unicode. Furthermore, the :mod:`socket` module 1428transparently converts Unicode host names to ACE, so that applications need not 1429be concerned about converting host names themselves when they pass them to the 1430socket module. On top of that, modules that have host names as function 1431parameters, such as :mod:`http.client` and :mod:`ftplib`, accept Unicode host 1432names (:mod:`http.client` then also transparently sends an IDNA hostname in the 1433:mailheader:`Host` field if it sends that field at all). 1434 1435.. _section 3.1: https://tools.ietf.org/html/rfc3490#section-3.1 1436 1437When receiving host names from the wire (such as in reverse name lookup), no 1438automatic conversion to Unicode is performed: Applications wishing to present 1439such host names to the user should decode them to Unicode. 1440 1441The module :mod:`encodings.idna` also implements the nameprep procedure, which 1442performs certain normalizations on host names, to achieve case-insensitivity of 1443international domain names, and to unify similar characters. The nameprep 1444functions can be used directly if desired. 1445 1446 1447.. function:: nameprep(label) 1448 1449 Return the nameprepped version of *label*. The implementation currently assumes 1450 query strings, so ``AllowUnassigned`` is true. 1451 1452 1453.. function:: ToASCII(label) 1454 1455 Convert a label to ASCII, as specified in :rfc:`3490`. ``UseSTD3ASCIIRules`` is 1456 assumed to be false. 1457 1458 1459.. function:: ToUnicode(label) 1460 1461 Convert a label to Unicode, as specified in :rfc:`3490`. 1462 1463 1464:mod:`encodings.mbcs` --- Windows ANSI codepage 1465----------------------------------------------- 1466 1467.. module:: encodings.mbcs 1468 :synopsis: Windows ANSI codepage 1469 1470Encode operand according to the ANSI codepage (CP_ACP). 1471 1472Availability: Windows only. 1473 1474.. versionchanged:: 3.3 1475 Support any error handler. 1476 1477.. versionchanged:: 3.2 1478 Before 3.2, the *errors* argument was ignored; ``'replace'`` was always used 1479 to encode, and ``'ignore'`` to decode. 1480 1481 1482:mod:`encodings.utf_8_sig` --- UTF-8 codec with BOM signature 1483------------------------------------------------------------- 1484 1485.. module:: encodings.utf_8_sig 1486 :synopsis: UTF-8 codec with BOM signature 1487.. moduleauthor:: Walter Dörwald 1488 1489This module implements a variant of the UTF-8 codec: On encoding a UTF-8 encoded 1490BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this 1491is only done once (on the first write to the byte stream). For decoding an 1492optional UTF-8 encoded BOM at the start of the data will be skipped. 1493