393 lines
13 KiB
Python
393 lines
13 KiB
Python
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"""Interface to the libbzip2 compression library.
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This module provides a file interface, classes for incremental
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(de)compression, and functions for one-shot (de)compression.
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"""
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__all__ = ["BZ2File", "BZ2Compressor", "BZ2Decompressor", "compress",
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"decompress"]
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__author__ = "Nadeem Vawda <nadeem.vawda@gmail.com>"
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import io
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import threading
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import warnings
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from _bz2 import BZ2Compressor, BZ2Decompressor
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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 BZ2File(io.BufferedIOBase):
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"""A file object providing transparent bzip2 (de)compression.
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A BZ2File can act as a wrapper for an existing file object, or refer
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directly to a named file on disk.
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Note that BZ2File provides a *binary* file interface - data read is
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returned as bytes, and data to be written should be given as bytes.
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"""
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def __init__(self, filename=None, mode="r", buffering=None,
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compresslevel=9, fileobj=None):
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"""Open a bzip2-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), or 'w' for writing.
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buffering is ignored. Its use is deprecated.
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If mode is 'w', compresslevel can be a number between 1 and 9
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specifying the level of compression: 1 produces the least
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compression, and 9 (default) produces the most compression.
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"""
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# This lock must be recursive, so that BufferedIOBase's
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# readline(), readlines() and writelines() don't deadlock.
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self._lock = threading.RLock()
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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 buffering is not None:
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warnings.warn("Use of 'buffering' argument is deprecated",
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DeprecationWarning)
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if not (1 <= compresslevel <= 9):
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raise ValueError("compresslevel must be between 1 and 9")
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if mode in ("", "r", "rb"):
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mode = "rb"
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mode_code = _MODE_READ
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self._decompressor = BZ2Decompressor()
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self._buffer = None
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elif mode in ("w", "wb"):
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mode = "wb"
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mode_code = _MODE_WRITE
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self._compressor = BZ2Compressor()
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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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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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with self._lock:
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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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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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self._buffer = None
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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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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()
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def readable(self):
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"""Return whether the file was opened for reading."""
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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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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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self._check_not_closed()
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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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self._check_not_closed()
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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.seekable():
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self._check_not_closed()
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raise io.UnsupportedOperation("Seeking is only supported "
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"on files opening for reading")
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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.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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rawblock = self._fp.read(_BUFFER_SIZE)
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if not rawblock:
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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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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, n=0):
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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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with self._lock:
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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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with self._lock:
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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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with self._lock:
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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 readinto(self, b):
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"""Read up to len(b) bytes into b.
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Returns the number of bytes read (0 for EOF).
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"""
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with self._lock:
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return io.BufferedIOBase.readinto(self, b)
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def readline(self, size=-1):
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"""Read a line of uncompressed bytes from the file.
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The terminating newline (if present) is retained. If size is
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non-negative, no more than size bytes will be read (in which
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case the line may be incomplete). Returns b'' if already at EOF.
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"""
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if not hasattr(size, "__index__"):
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raise TypeError("Integer argument expected")
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size = size.__index__()
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with self._lock:
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return io.BufferedIOBase.readline(self, size)
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def readlines(self, size=-1):
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"""Read a list of lines of uncompressed bytes from the file.
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size can be specified to control the number of lines read: no
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further lines will be read once the total size of the lines read
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so far equals or exceeds size.
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"""
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if not hasattr(size, "__index__"):
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raise TypeError("Integer argument expected")
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size = size.__index__()
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with self._lock:
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return io.BufferedIOBase.readlines(self, size)
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def write(self, data):
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"""Write a byte string 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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with self._lock:
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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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def writelines(self, seq):
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"""Write a sequence of byte strings to the file.
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Returns the number of uncompressed bytes written.
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seq can be any iterable yielding byte strings.
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Line separators are not added between the written byte strings.
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"""
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with self._lock:
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return io.BufferedIOBase.writelines(self, seq)
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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 = BZ2Decompressor()
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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. 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, so depending on the parameters,
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this operation may be extremely slow.
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"""
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with self._lock:
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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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with self._lock:
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self._check_not_closed()
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return self._pos
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def compress(data, compresslevel=9):
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"""Compress a block of data.
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compresslevel, if given, must be a number between 1 and 9.
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For incremental compression, use a BZ2Compressor object instead.
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"""
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comp = BZ2Compressor(compresslevel)
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return comp.compress(data) + comp.flush()
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def decompress(data):
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"""Decompress a block of data.
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For incremental decompression, use a BZ2Decompressor object instead.
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"""
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if len(data) == 0:
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return b""
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decomp = BZ2Decompressor()
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result = decomp.decompress(data)
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if not decomp.eof:
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raise ValueError("Compressed data ended before the "
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"end-of-stream marker was reached")
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return result
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