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636 lines
19 KiB
636 lines
19 KiB
""" codecs -- Python Codec Registry, API and helpers. |
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Written by Marc-Andre Lemburg (mal@lemburg.com). |
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(c) Copyright CNRI, All Rights Reserved. NO WARRANTY. |
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"""#" |
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import struct, __builtin__ |
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### Registry and builtin stateless codec functions |
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try: |
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from _codecs import * |
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except ImportError, why: |
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raise SystemError,\ |
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'Failed to load the builtin codecs: %s' % why |
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__all__ = ["register", "lookup", "open", "EncodedFile", "BOM", "BOM_BE", |
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"BOM_LE", "BOM32_BE", "BOM32_LE", "BOM64_BE", "BOM64_LE"] |
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### Constants |
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# |
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# Byte Order Mark (BOM) and its possible values (BOM_BE, BOM_LE) |
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# |
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BOM = struct.pack('=H', 0xFEFF) |
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# |
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BOM_BE = BOM32_BE = '\376\377' |
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# corresponds to Unicode U+FEFF in UTF-16 on big endian |
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# platforms == ZERO WIDTH NO-BREAK SPACE |
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BOM_LE = BOM32_LE = '\377\376' |
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# corresponds to Unicode U+FFFE in UTF-16 on little endian |
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# platforms == defined as being an illegal Unicode character |
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# |
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# 64-bit Byte Order Marks |
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# |
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BOM64_BE = '\000\000\376\377' |
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# corresponds to Unicode U+0000FEFF in UCS-4 |
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BOM64_LE = '\377\376\000\000' |
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# corresponds to Unicode U+0000FFFE in UCS-4 |
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### Codec base classes (defining the API) |
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class Codec: |
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""" Defines the interface for stateless encoders/decoders. |
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The .encode()/.decode() methods may implement different error |
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handling schemes by providing the errors argument. These |
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string values are defined: |
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'strict' - raise a ValueError error (or a subclass) |
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'ignore' - ignore the character and continue with the next |
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'replace' - replace with a suitable replacement character; |
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Python will use the official U+FFFD REPLACEMENT |
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CHARACTER for the builtin Unicode codecs. |
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""" |
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def encode(self, input, errors='strict'): |
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""" Encodes the object input and returns a tuple (output |
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object, length consumed). |
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errors defines the error handling to apply. It defaults to |
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'strict' handling. |
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The method may not store state in the Codec instance. Use |
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StreamCodec for codecs which have to keep state in order to |
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make encoding/decoding efficient. |
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The encoder must be able to handle zero length input and |
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return an empty object of the output object type in this |
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situation. |
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""" |
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raise NotImplementedError |
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def decode(self, input, errors='strict'): |
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""" Decodes the object input and returns a tuple (output |
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object, length consumed). |
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input must be an object which provides the bf_getreadbuf |
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buffer slot. Python strings, buffer objects and memory |
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mapped files are examples of objects providing this slot. |
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errors defines the error handling to apply. It defaults to |
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'strict' handling. |
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The method may not store state in the Codec instance. Use |
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StreamCodec for codecs which have to keep state in order to |
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make encoding/decoding efficient. |
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The decoder must be able to handle zero length input and |
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return an empty object of the output object type in this |
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situation. |
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""" |
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raise NotImplementedError |
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# |
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# The StreamWriter and StreamReader class provide generic working |
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# interfaces which can be used to implement new encoding submodules |
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# very easily. See encodings/utf_8.py for an example on how this is |
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# done. |
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# |
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class StreamWriter(Codec): |
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def __init__(self, stream, errors='strict'): |
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""" Creates a StreamWriter instance. |
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stream must be a file-like object open for writing |
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(binary) data. |
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The StreamWriter may implement different error handling |
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schemes by providing the errors keyword argument. These |
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parameters are defined: |
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'strict' - raise a ValueError (or a subclass) |
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'ignore' - ignore the character and continue with the next |
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'replace'- replace with a suitable replacement character |
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""" |
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self.stream = stream |
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self.errors = errors |
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def write(self, object): |
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""" Writes the object's contents encoded to self.stream. |
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""" |
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data, consumed = self.encode(object, self.errors) |
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self.stream.write(data) |
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def writelines(self, list): |
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""" Writes the concatenated list of strings to the stream |
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using .write(). |
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""" |
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self.write(''.join(list)) |
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def reset(self): |
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""" Flushes and resets the codec buffers used for keeping state. |
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Calling this method should ensure that the data on the |
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output is put into a clean state, that allows appending |
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of new fresh data without having to rescan the whole |
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stream to recover state. |
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""" |
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pass |
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def __getattr__(self, name, |
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getattr=getattr): |
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""" Inherit all other methods from the underlying stream. |
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""" |
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return getattr(self.stream, name) |
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### |
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class StreamReader(Codec): |
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def __init__(self, stream, errors='strict'): |
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""" Creates a StreamReader instance. |
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stream must be a file-like object open for reading |
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(binary) data. |
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The StreamReader may implement different error handling |
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schemes by providing the errors keyword argument. These |
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parameters are defined: |
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'strict' - raise a ValueError (or a subclass) |
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'ignore' - ignore the character and continue with the next |
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'replace'- replace with a suitable replacement character; |
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""" |
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self.stream = stream |
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self.errors = errors |
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def read(self, size=-1): |
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""" Decodes data from the stream self.stream and returns the |
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resulting object. |
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size indicates the approximate maximum number of bytes to |
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read from the stream for decoding purposes. The decoder |
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can modify this setting as appropriate. The default value |
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-1 indicates to read and decode as much as possible. size |
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is intended to prevent having to decode huge files in one |
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step. |
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The method should use a greedy read strategy meaning that |
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it should read as much data as is allowed within the |
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definition of the encoding and the given size, e.g. if |
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optional encoding endings or state markers are available |
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on the stream, these should be read too. |
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""" |
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# Unsliced reading: |
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if size < 0: |
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return self.decode(self.stream.read(), self.errors)[0] |
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# Sliced reading: |
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read = self.stream.read |
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decode = self.decode |
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data = read(size) |
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i = 0 |
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while 1: |
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try: |
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object, decodedbytes = decode(data, self.errors) |
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except ValueError, why: |
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# This method is slow but should work under pretty much |
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# all conditions; at most 10 tries are made |
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i = i + 1 |
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newdata = read(1) |
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if not newdata or i > 10: |
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raise |
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data = data + newdata |
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else: |
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return object |
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def readline(self, size=None): |
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""" Read one line from the input stream and return the |
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decoded data. |
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Note: Unlike the .readlines() method, this method inherits |
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the line breaking knowledge from the underlying stream's |
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.readline() method -- there is currently no support for |
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line breaking using the codec decoder due to lack of line |
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buffering. Sublcasses should however, if possible, try to |
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implement this method using their own knowledge of line |
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breaking. |
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size, if given, is passed as size argument to the stream's |
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.readline() method. |
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""" |
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if size is None: |
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line = self.stream.readline() |
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else: |
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line = self.stream.readline(size) |
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return self.decode(line, self.errors)[0] |
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def readlines(self, sizehint=None): |
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""" Read all lines available on the input stream |
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and return them as list of lines. |
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Line breaks are implemented using the codec's decoder |
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method and are included in the list entries. |
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sizehint, if given, is passed as size argument to the |
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stream's .read() method. |
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""" |
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if sizehint is None: |
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data = self.stream.read() |
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else: |
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data = self.stream.read(sizehint) |
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return self.decode(data, self.errors)[0].splitlines(1) |
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def reset(self): |
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""" Resets the codec buffers used for keeping state. |
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Note that no stream repositioning should take place. |
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This method is primarily intended to be able to recover |
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from decoding errors. |
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""" |
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pass |
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def __getattr__(self, name, |
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getattr=getattr): |
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""" Inherit all other methods from the underlying stream. |
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""" |
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return getattr(self.stream, name) |
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### |
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class StreamReaderWriter: |
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""" StreamReaderWriter instances allow wrapping streams which |
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work in both read and write modes. |
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The design is such that one can use the factory functions |
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returned by the codec.lookup() function to construct the |
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instance. |
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""" |
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# Optional attributes set by the file wrappers below |
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encoding = 'unknown' |
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def __init__(self, stream, Reader, Writer, errors='strict'): |
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""" Creates a StreamReaderWriter instance. |
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stream must be a Stream-like object. |
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Reader, Writer must be factory functions or classes |
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providing the StreamReader, StreamWriter interface resp. |
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Error handling is done in the same way as defined for the |
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StreamWriter/Readers. |
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""" |
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self.stream = stream |
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self.reader = Reader(stream, errors) |
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self.writer = Writer(stream, errors) |
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self.errors = errors |
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def read(self, size=-1): |
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return self.reader.read(size) |
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def readline(self, size=None): |
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return self.reader.readline(size) |
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def readlines(self, sizehint=None): |
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return self.reader.readlines(sizehint) |
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def write(self, data): |
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return self.writer.write(data) |
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def writelines(self, list): |
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return self.writer.writelines(list) |
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def reset(self): |
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self.reader.reset() |
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self.writer.reset() |
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def __getattr__(self, name, |
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getattr=getattr): |
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""" Inherit all other methods from the underlying stream. |
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""" |
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return getattr(self.stream, name) |
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### |
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class StreamRecoder: |
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""" StreamRecoder instances provide a frontend - backend |
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view of encoding data. |
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They use the complete set of APIs returned by the |
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codecs.lookup() function to implement their task. |
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Data written to the stream is first decoded into an |
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intermediate format (which is dependent on the given codec |
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combination) and then written to the stream using an instance |
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of the provided Writer class. |
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In the other direction, data is read from the stream using a |
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Reader instance and then return encoded data to the caller. |
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""" |
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# Optional attributes set by the file wrappers below |
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data_encoding = 'unknown' |
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file_encoding = 'unknown' |
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def __init__(self, stream, encode, decode, Reader, Writer, |
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errors='strict'): |
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""" Creates a StreamRecoder instance which implements a two-way |
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conversion: encode and decode work on the frontend (the |
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input to .read() and output of .write()) while |
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Reader and Writer work on the backend (reading and |
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writing to the stream). |
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You can use these objects to do transparent direct |
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recodings from e.g. latin-1 to utf-8 and back. |
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stream must be a file-like object. |
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encode, decode must adhere to the Codec interface, Reader, |
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Writer must be factory functions or classes providing the |
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StreamReader, StreamWriter interface resp. |
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encode and decode are needed for the frontend translation, |
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Reader and Writer for the backend translation. Unicode is |
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used as intermediate encoding. |
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Error handling is done in the same way as defined for the |
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StreamWriter/Readers. |
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""" |
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self.stream = stream |
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self.encode = encode |
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self.decode = decode |
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self.reader = Reader(stream, errors) |
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self.writer = Writer(stream, errors) |
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self.errors = errors |
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def read(self, size=-1): |
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data = self.reader.read(size) |
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data, bytesencoded = self.encode(data, self.errors) |
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return data |
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def readline(self, size=None): |
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if size is None: |
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data = self.reader.readline() |
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else: |
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data = self.reader.readline(size) |
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data, bytesencoded = self.encode(data, self.errors) |
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return data |
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def readlines(self, sizehint=None): |
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if sizehint is None: |
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data = self.reader.read() |
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else: |
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data = self.reader.read(sizehint) |
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data, bytesencoded = self.encode(data, self.errors) |
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return data.splitlines(1) |
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def write(self, data): |
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data, bytesdecoded = self.decode(data, self.errors) |
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return self.writer.write(data) |
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def writelines(self, list): |
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data = ''.join(list) |
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data, bytesdecoded = self.decode(data, self.errors) |
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return self.writer.write(data) |
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def reset(self): |
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self.reader.reset() |
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self.writer.reset() |
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def __getattr__(self, name, |
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getattr=getattr): |
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""" Inherit all other methods from the underlying stream. |
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""" |
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return getattr(self.stream, name) |
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### Shortcuts |
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def open(filename, mode='rb', encoding=None, errors='strict', buffering=1): |
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""" Open an encoded file using the given mode and return |
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a wrapped version providing transparent encoding/decoding. |
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Note: The wrapped version will only accept the object format |
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defined by the codecs, i.e. Unicode objects for most builtin |
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codecs. Output is also codec dependent and will usually by |
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Unicode as well. |
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Files are always opened in binary mode, even if no binary mode |
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was specified. Thisis done to avoid data loss due to encodings |
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using 8-bit values. The default file mode is 'rb' meaning to |
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open the file in binary read mode. |
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encoding specifies the encoding which is to be used for the |
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the file. |
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errors may be given to define the error handling. It defaults |
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to 'strict' which causes ValueErrors to be raised in case an |
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encoding error occurs. |
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buffering has the same meaning as for the builtin open() API. |
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It defaults to line buffered. |
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The returned wrapped file object provides an extra attribute |
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.encoding which allows querying the used encoding. This |
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attribute is only available if an encoding was specified as |
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parameter. |
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""" |
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if encoding is not None and \ |
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'b' not in mode: |
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# Force opening of the file in binary mode |
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mode = mode + 'b' |
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file = __builtin__.open(filename, mode, buffering) |
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if encoding is None: |
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return file |
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(e, d, sr, sw) = lookup(encoding) |
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srw = StreamReaderWriter(file, sr, sw, errors) |
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# Add attributes to simplify introspection |
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srw.encoding = encoding |
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return srw |
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def EncodedFile(file, data_encoding, file_encoding=None, errors='strict'): |
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""" Return a wrapped version of file which provides transparent |
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encoding translation. |
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Strings written to the wrapped file are interpreted according |
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to the given data_encoding and then written to the original |
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file as string using file_encoding. The intermediate encoding |
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will usually be Unicode but depends on the specified codecs. |
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Strings are read from the file using file_encoding and then |
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passed back to the caller as string using data_encoding. |
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If file_encoding is not given, it defaults to data_encoding. |
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errors may be given to define the error handling. It defaults |
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to 'strict' which causes ValueErrors to be raised in case an |
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encoding error occurs. |
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The returned wrapped file object provides two extra attributes |
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.data_encoding and .file_encoding which reflect the given |
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parameters of the same name. The attributes can be used for |
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introspection by Python programs. |
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""" |
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if file_encoding is None: |
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file_encoding = data_encoding |
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encode, decode = lookup(data_encoding)[:2] |
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Reader, Writer = lookup(file_encoding)[2:] |
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sr = StreamRecoder(file, |
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encode, decode, Reader, Writer, |
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errors) |
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# Add attributes to simplify introspection |
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sr.data_encoding = data_encoding |
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sr.file_encoding = file_encoding |
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return sr |
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### Helpers for codec lookup |
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def getencoder(encoding): |
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""" Lookup up the codec for the given encoding and return |
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its encoder function. |
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Raises a LookupError in case the encoding cannot be found. |
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""" |
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return lookup(encoding)[0] |
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def getdecoder(encoding): |
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""" Lookup up the codec for the given encoding and return |
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its decoder function. |
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Raises a LookupError in case the encoding cannot be found. |
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""" |
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return lookup(encoding)[1] |
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def getreader(encoding): |
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""" Lookup up the codec for the given encoding and return |
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its StreamReader class or factory function. |
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Raises a LookupError in case the encoding cannot be found. |
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""" |
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return lookup(encoding)[2] |
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def getwriter(encoding): |
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""" Lookup up the codec for the given encoding and return |
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its StreamWriter class or factory function. |
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Raises a LookupError in case the encoding cannot be found. |
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""" |
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return lookup(encoding)[3] |
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### Helpers for charmap-based codecs |
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def make_identity_dict(rng): |
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""" make_identity_dict(rng) -> dict |
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Return a dictionary where elements of the rng sequence are |
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mapped to themselves. |
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""" |
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res = {} |
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for i in rng: |
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res[i]=i |
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return res |
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def make_encoding_map(decoding_map): |
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""" Creates an encoding map from a decoding map. |
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If a target mapping in the decoding map occurrs multiple |
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times, then that target is mapped to None (undefined mapping), |
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causing an exception when encountered by the charmap codec |
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during translation. |
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One example where this happens is cp875.py which decodes |
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multiple character to \u001a. |
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""" |
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m = {} |
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for k,v in decoding_map.items(): |
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if not m.has_key(v): |
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m[v] = k |
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else: |
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m[v] = None |
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return m |
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# Tell modulefinder that using codecs probably needs the encodings |
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# package |
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_false = 0 |
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if _false: |
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import encodings |
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### Tests |
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if __name__ == '__main__': |
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import sys |
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# Make stdout translate Latin-1 output into UTF-8 output |
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sys.stdout = EncodedFile(sys.stdout, 'latin-1', 'utf-8') |
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# Have stdin translate Latin-1 input into UTF-8 input |
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sys.stdin = EncodedFile(sys.stdin, 'utf-8', 'latin-1')
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