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401 lines
14 KiB
Python
401 lines
14 KiB
Python
"""Interface to the liblzma compression library.
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This module provides a class for reading and writing compressed files,
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classes for incremental (de)compression, and convenience functions for
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one-shot (de)compression.
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These classes and functions support both the XZ and legacy LZMA
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container formats, as well as raw compressed data streams.
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"""
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__all__ = [
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"CHECK_NONE", "CHECK_CRC32", "CHECK_CRC64", "CHECK_SHA256",
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"CHECK_ID_MAX", "CHECK_UNKNOWN",
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"FILTER_LZMA1", "FILTER_LZMA2", "FILTER_DELTA", "FILTER_X86", "FILTER_IA64",
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"FILTER_ARM", "FILTER_ARMTHUMB", "FILTER_POWERPC", "FILTER_SPARC",
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"FORMAT_AUTO", "FORMAT_XZ", "FORMAT_ALONE", "FORMAT_RAW",
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"MF_HC3", "MF_HC4", "MF_BT2", "MF_BT3", "MF_BT4",
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"MODE_FAST", "MODE_NORMAL", "PRESET_DEFAULT", "PRESET_EXTREME",
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"LZMACompressor", "LZMADecompressor", "LZMAFile", "LZMAError",
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"compress", "decompress", "check_is_supported",
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]
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import io
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from _lzma import *
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_MODE_CLOSED = 0
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_MODE_READ = 1
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_MODE_READ_EOF = 2
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_MODE_WRITE = 3
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_BUFFER_SIZE = 8192
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class LZMAFile(io.BufferedIOBase):
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"""A file object providing transparent LZMA (de)compression.
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An LZMAFile can act as a wrapper for an existing file object, or
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refer directly to a named file on disk.
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Note that LZMAFile provides a *binary* file interface - data read
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is returned as bytes, and data to be written must be given as bytes.
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"""
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def __init__(self, filename=None, mode="r", *,
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fileobj=None, format=None, check=-1,
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preset=None, filters=None):
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"""Open an LZMA-compressed file.
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If filename is given, open the named file. Otherwise, operate on
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the file object given by fileobj. Exactly one of these two
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parameters should be provided.
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mode can be "r" for reading (default), "w" for (over)writing, or
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"a" for appending.
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format specifies the container format to use for the file.
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If mode is "r", this defaults to FORMAT_AUTO. Otherwise, the
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default is FORMAT_XZ.
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check specifies the integrity check to use. This argument can
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only be used when opening a file for writing. For FORMAT_XZ,
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the default is CHECK_CRC64. FORMAT_ALONE and FORMAT_RAW do not
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support integrity checks - for these formats, check must be
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omitted, or be CHECK_NONE.
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When opening a file for reading, the *preset* argument is not
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meaningful, and should be omitted. The *filters* argument should
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also be omitted, except when format is FORMAT_RAW (in which case
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it is required).
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When opening a file for writing, the settings used by the
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compressor can be specified either as a preset compression
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level (with the *preset* argument), or in detail as a custom
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filter chain (with the *filters* argument). For FORMAT_XZ and
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FORMAT_ALONE, the default is to use the PRESET_DEFAULT preset
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level. For FORMAT_RAW, the caller must always specify a filter
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chain; the raw compressor does not support preset compression
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levels.
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preset (if provided) should be an integer in the range 0-9,
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optionally OR-ed with the constant PRESET_EXTREME.
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filters (if provided) should be a sequence of dicts. Each dict
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should have an entry for "id" indicating ID of the filter, plus
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additional entries for options to the filter.
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"""
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self._fp = None
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self._closefp = False
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self._mode = _MODE_CLOSED
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self._pos = 0
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self._size = -1
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if mode == "r":
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if check != -1:
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raise ValueError("Cannot specify an integrity check "
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"when opening a file for reading")
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if preset is not None:
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raise ValueError("Cannot specify a preset compression "
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"level when opening a file for reading")
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if format is None:
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format = FORMAT_AUTO
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mode_code = _MODE_READ
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# Save the args to pass to the LZMADecompressor initializer.
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# If the file contains multiple compressed streams, each
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# stream will need a separate decompressor object.
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self._init_args = {"format":format, "filters":filters}
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self._decompressor = LZMADecompressor(**self._init_args)
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self._buffer = None
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elif mode in ("w", "a"):
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if format is None:
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format = FORMAT_XZ
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mode_code = _MODE_WRITE
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self._compressor = LZMACompressor(format=format, check=check,
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preset=preset, filters=filters)
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else:
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raise ValueError("Invalid mode: {!r}".format(mode))
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if filename is not None and fileobj is None:
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mode += "b"
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self._fp = open(filename, mode)
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self._closefp = True
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self._mode = mode_code
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elif fileobj is not None and filename is None:
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self._fp = fileobj
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self._mode = mode_code
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else:
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raise ValueError("Must give exactly one of filename and fileobj")
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def close(self):
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"""Flush and close the file.
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May be called more than once without error. Once the file is
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closed, any other operation on it will raise a ValueError.
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"""
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if self._mode == _MODE_CLOSED:
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return
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try:
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if self._mode in (_MODE_READ, _MODE_READ_EOF):
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self._decompressor = None
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self._buffer = None
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elif self._mode == _MODE_WRITE:
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self._fp.write(self._compressor.flush())
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self._compressor = None
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finally:
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try:
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if self._closefp:
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self._fp.close()
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finally:
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self._fp = None
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self._closefp = False
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self._mode = _MODE_CLOSED
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@property
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def closed(self):
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"""True if this file is closed."""
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return self._mode == _MODE_CLOSED
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def fileno(self):
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"""Return the file descriptor for the underlying file."""
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self._check_not_closed()
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return self._fp.fileno()
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def seekable(self):
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"""Return whether the file supports seeking."""
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return self.readable() and self._fp.seekable()
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def readable(self):
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"""Return whether the file was opened for reading."""
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self._check_not_closed()
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return self._mode in (_MODE_READ, _MODE_READ_EOF)
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def writable(self):
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"""Return whether the file was opened for writing."""
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self._check_not_closed()
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return self._mode == _MODE_WRITE
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# Mode-checking helper functions.
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def _check_not_closed(self):
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if self.closed:
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raise ValueError("I/O operation on closed file")
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def _check_can_read(self):
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if not self.readable():
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raise io.UnsupportedOperation("File not open for reading")
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def _check_can_write(self):
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if not self.writable():
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raise io.UnsupportedOperation("File not open for writing")
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def _check_can_seek(self):
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if not self.readable():
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raise io.UnsupportedOperation("Seeking is only supported "
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"on files open for reading")
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if not self._fp.seekable():
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raise io.UnsupportedOperation("The underlying file object "
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"does not support seeking")
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# Fill the readahead buffer if it is empty. Returns False on EOF.
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def _fill_buffer(self):
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if self._buffer:
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return True
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if self._decompressor.unused_data:
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rawblock = self._decompressor.unused_data
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else:
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rawblock = self._fp.read(_BUFFER_SIZE)
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if not rawblock:
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if self._decompressor.eof:
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self._mode = _MODE_READ_EOF
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self._size = self._pos
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return False
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else:
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raise EOFError("Compressed file ended before the "
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"end-of-stream marker was reached")
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# Continue to next stream.
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if self._decompressor.eof:
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self._decompressor = LZMADecompressor(**self._init_args)
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self._buffer = self._decompressor.decompress(rawblock)
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return True
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# Read data until EOF.
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# If return_data is false, consume the data without returning it.
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def _read_all(self, return_data=True):
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blocks = []
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while self._fill_buffer():
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if return_data:
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blocks.append(self._buffer)
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self._pos += len(self._buffer)
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self._buffer = None
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if return_data:
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return b"".join(blocks)
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# Read a block of up to n bytes.
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# If return_data is false, consume the data without returning it.
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def _read_block(self, n, return_data=True):
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blocks = []
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while n > 0 and self._fill_buffer():
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if n < len(self._buffer):
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data = self._buffer[:n]
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self._buffer = self._buffer[n:]
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else:
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data = self._buffer
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self._buffer = None
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if return_data:
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blocks.append(data)
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self._pos += len(data)
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n -= len(data)
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if return_data:
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return b"".join(blocks)
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def peek(self, size=-1):
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"""Return buffered data without advancing the file position.
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Always returns at least one byte of data, unless at EOF.
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The exact number of bytes returned is unspecified.
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"""
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self._check_can_read()
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if self._mode == _MODE_READ_EOF or not self._fill_buffer():
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return b""
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return self._buffer
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def read(self, size=-1):
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"""Read up to size uncompressed bytes from the file.
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If size is negative or omitted, read until EOF is reached.
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Returns b"" if the file is already at EOF.
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"""
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self._check_can_read()
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if self._mode == _MODE_READ_EOF or size == 0:
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return b""
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elif size < 0:
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return self._read_all()
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else:
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return self._read_block(size)
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def read1(self, size=-1):
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"""Read up to size uncompressed bytes with at most one read
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from the underlying stream.
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Returns b"" if the file is at EOF.
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"""
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self._check_can_read()
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if (size == 0 or self._mode == _MODE_READ_EOF or
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not self._fill_buffer()):
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return b""
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if 0 < size < len(self._buffer):
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data = self._buffer[:size]
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self._buffer = self._buffer[size:]
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else:
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data = self._buffer
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self._buffer = None
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self._pos += len(data)
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return data
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def write(self, data):
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"""Write a bytes object to the file.
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Returns the number of uncompressed bytes written, which is
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always len(data). Note that due to buffering, the file on disk
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may not reflect the data written until close() is called.
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"""
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self._check_can_write()
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compressed = self._compressor.compress(data)
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self._fp.write(compressed)
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self._pos += len(data)
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return len(data)
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# Rewind the file to the beginning of the data stream.
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def _rewind(self):
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self._fp.seek(0, 0)
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self._mode = _MODE_READ
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self._pos = 0
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self._decompressor = LZMADecompressor(**self._init_args)
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self._buffer = None
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def seek(self, offset, whence=0):
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"""Change the file position.
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The new position is specified by offset, relative to the
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position indicated by whence. Possible values for whence are:
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0: start of stream (default): offset must not be negative
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1: current stream position
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2: end of stream; offset must not be positive
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Returns the new file position.
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Note that seeking is emulated, sp depending on the parameters,
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this operation may be extremely slow.
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"""
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self._check_can_seek()
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# Recalculate offset as an absolute file position.
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if whence == 0:
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pass
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elif whence == 1:
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offset = self._pos + offset
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elif whence == 2:
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# Seeking relative to EOF - we need to know the file's size.
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if self._size < 0:
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self._read_all(return_data=False)
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offset = self._size + offset
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else:
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raise ValueError("Invalid value for whence: {}".format(whence))
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# Make it so that offset is the number of bytes to skip forward.
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if offset < self._pos:
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self._rewind()
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else:
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offset -= self._pos
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# Read and discard data until we reach the desired position.
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if self._mode != _MODE_READ_EOF:
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self._read_block(offset, return_data=False)
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return self._pos
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def tell(self):
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"""Return the current file position."""
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self._check_not_closed()
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return self._pos
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def compress(data, format=FORMAT_XZ, check=-1, preset=None, filters=None):
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"""Compress a block of data.
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Refer to LZMACompressor's docstring for a description of the
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optional arguments *format*, *check*, *preset* and *filters*.
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For incremental compression, use an LZMACompressor object instead.
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"""
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comp = LZMACompressor(format, check, preset, filters)
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return comp.compress(data) + comp.flush()
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def decompress(data, format=FORMAT_AUTO, memlimit=None, filters=None):
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"""Decompress a block of data.
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Refer to LZMADecompressor's docstring for a description of the
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optional arguments *format*, *check* and *filters*.
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For incremental decompression, use a LZMADecompressor object instead.
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"""
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results = []
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while True:
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decomp = LZMADecompressor(format, memlimit, filters)
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results.append(decomp.decompress(data))
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if not decomp.eof:
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raise LZMAError("Compressed data ended before the "
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"end-of-stream marker was reached")
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if not decomp.unused_data:
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return b"".join(results)
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# There is unused data left over. Proceed to next stream.
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data = decomp.unused_data
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