mirror of
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510 lines
17 KiB
Python
510 lines
17 KiB
Python
"""Functions that read and write gzipped files.
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The user of the file doesn't have to worry about the compression,
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but random access is not allowed."""
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# based on Andrew Kuchling's minigzip.py distributed with the zlib module
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import struct, sys, time
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import zlib
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import builtins
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__all__ = ["GzipFile","open"]
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FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
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READ, WRITE = 1, 2
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def U32(i):
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"""Return i as an unsigned integer, assuming it fits in 32 bits.
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If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.
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"""
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if i < 0:
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i += 1 << 32
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return i
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def LOWU32(i):
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"""Return the low-order 32 bits of an int, as a non-negative int."""
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return i & 0xFFFFFFFF
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def write32(output, value):
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output.write(struct.pack("<l", value))
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def write32u(output, value):
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# The L format writes the bit pattern correctly whether signed
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# or unsigned.
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output.write(struct.pack("<L", value))
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def read32(input):
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return struct.unpack("<l", input.read(4))[0]
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def open(filename, mode="rb", compresslevel=9):
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"""Shorthand for GzipFile(filename, mode, compresslevel).
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The filename argument is required; mode defaults to 'rb'
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and compresslevel defaults to 9.
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"""
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return GzipFile(filename, mode, compresslevel)
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class GzipFile:
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"""The GzipFile class simulates most of the methods of a file object with
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the exception of the readinto() and truncate() methods.
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"""
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myfileobj = None
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max_read_chunk = 10 * 1024 * 1024 # 10Mb
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def __init__(self, filename=None, mode=None,
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compresslevel=9, fileobj=None):
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"""Constructor for the GzipFile class.
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At least one of fileobj and filename must be given a
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non-trivial value.
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The new class instance is based on fileobj, which can be a regular
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file, a StringIO object, or any other object which simulates a file.
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It defaults to None, in which case filename is opened to provide
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a file object.
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When fileobj is not None, the filename argument is only used to be
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included in the gzip file header, which may includes the original
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filename of the uncompressed file. It defaults to the filename of
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fileobj, if discernible; otherwise, it defaults to the empty string,
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and in this case the original filename is not included in the header.
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The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', or 'wb',
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depending on whether the file will be read or written. The default
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is the mode of fileobj if discernible; otherwise, the default is 'rb'.
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Be aware that only the 'rb', 'ab', and 'wb' values should be used
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for cross-platform portability.
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The compresslevel argument is an integer from 1 to 9 controlling the
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level of compression; 1 is fastest and produces the least compression,
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and 9 is slowest and produces the most compression. The default is 9.
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"""
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# guarantee the file is opened in binary mode on platforms
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# that care about that sort of thing
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if mode and 'b' not in mode:
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mode += 'b'
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if fileobj is None:
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fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
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if filename is None:
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if hasattr(fileobj, 'name'): filename = fileobj.name
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else: filename = ''
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if mode is None:
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if hasattr(fileobj, 'mode'): mode = fileobj.mode
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else: mode = 'rb'
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if mode[0:1] == 'r':
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self.mode = READ
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# Set flag indicating start of a new member
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self._new_member = True
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self.extrabuf = b""
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self.extrasize = 0
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self.name = filename
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# Starts small, scales exponentially
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self.min_readsize = 100
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elif mode[0:1] == 'w' or mode[0:1] == 'a':
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self.mode = WRITE
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self._init_write(filename)
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self.compress = zlib.compressobj(compresslevel,
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zlib.DEFLATED,
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-zlib.MAX_WBITS,
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zlib.DEF_MEM_LEVEL,
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0)
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else:
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raise IOError("Mode " + mode + " not supported")
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self.fileobj = fileobj
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self.offset = 0
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if self.mode == WRITE:
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self._write_gzip_header()
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@property
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def filename(self):
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import warnings
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warnings.warn("use the name attribute", DeprecationWarning)
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if self.mode == WRITE and self.name[-3:] != ".gz":
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return self.name + ".gz"
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return self.name
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def __repr__(self):
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s = repr(self.fileobj)
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return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'
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def _init_write(self, filename):
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self.name = filename
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self.crc = zlib.crc32("")
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self.size = 0
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self.writebuf = []
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self.bufsize = 0
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def _write_gzip_header(self):
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self.fileobj.write(b'\037\213') # magic header
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self.fileobj.write(b'\010') # compression method
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try:
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# RFC 1952 requires the FNAME field to be Latin-1. Do not
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# include filenames that cannot be represented that way.
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fname = self.name.encode('latin-1')
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if fname.endswith(b'.gz'):
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fname = fname[:-3]
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except UnicodeEncodeError:
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fname = b''
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flags = 0
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if fname:
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flags = FNAME
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self.fileobj.write(chr(flags).encode('latin-1'))
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write32u(self.fileobj, int(time.time()))
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self.fileobj.write(b'\002')
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self.fileobj.write(b'\377')
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if fname:
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self.fileobj.write(fname + b'\000')
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def _init_read(self):
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self.crc = zlib.crc32("")
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self.size = 0
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def _read_gzip_header(self):
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magic = self.fileobj.read(2)
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if magic != b'\037\213':
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raise IOError('Not a gzipped file')
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method = ord( self.fileobj.read(1) )
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if method != 8:
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raise IOError('Unknown compression method')
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flag = ord( self.fileobj.read(1) )
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# modtime = self.fileobj.read(4)
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# extraflag = self.fileobj.read(1)
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# os = self.fileobj.read(1)
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self.fileobj.read(6)
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if flag & FEXTRA:
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# Read & discard the extra field, if present
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xlen = ord(self.fileobj.read(1))
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xlen = xlen + 256*ord(self.fileobj.read(1))
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self.fileobj.read(xlen)
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if flag & FNAME:
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# Read and discard a null-terminated string containing the filename
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while True:
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s = self.fileobj.read(1)
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if not s or s==b'\000':
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break
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if flag & FCOMMENT:
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# Read and discard a null-terminated string containing a comment
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while True:
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s = self.fileobj.read(1)
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if not s or s==b'\000':
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break
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if flag & FHCRC:
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self.fileobj.read(2) # Read & discard the 16-bit header CRC
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def write(self,data):
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if self.mode != WRITE:
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import errno
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raise IOError(errno.EBADF, "write() on read-only GzipFile object")
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if self.fileobj is None:
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raise ValueError("write() on closed GzipFile object")
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if len(data) > 0:
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self.size = self.size + len(data)
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self.crc = zlib.crc32(data, self.crc)
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self.fileobj.write( self.compress.compress(data) )
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self.offset += len(data)
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def read(self, size=-1):
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if self.mode != READ:
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import errno
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raise IOError(errno.EBADF, "read() on write-only GzipFile object")
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if self.extrasize <= 0 and self.fileobj is None:
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return b''
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readsize = 1024
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if size < 0: # get the whole thing
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try:
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while True:
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self._read(readsize)
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readsize = min(self.max_read_chunk, readsize * 2)
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except EOFError:
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size = self.extrasize
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else: # just get some more of it
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try:
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while size > self.extrasize:
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self._read(readsize)
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readsize = min(self.max_read_chunk, readsize * 2)
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except EOFError:
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if size > self.extrasize:
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size = self.extrasize
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chunk = self.extrabuf[:size]
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self.extrabuf = self.extrabuf[size:]
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self.extrasize = self.extrasize - size
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self.offset += size
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return chunk
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def _unread(self, buf):
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self.extrabuf = buf + self.extrabuf
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self.extrasize = len(buf) + self.extrasize
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self.offset -= len(buf)
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def _read(self, size=1024):
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if self.fileobj is None:
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raise EOFError("Reached EOF")
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if self._new_member:
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# If the _new_member flag is set, we have to
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# jump to the next member, if there is one.
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#
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# First, check if we're at the end of the file;
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# if so, it's time to stop; no more members to read.
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pos = self.fileobj.tell() # Save current position
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self.fileobj.seek(0, 2) # Seek to end of file
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if pos == self.fileobj.tell():
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raise EOFError("Reached EOF")
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else:
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self.fileobj.seek( pos ) # Return to original position
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self._init_read()
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self._read_gzip_header()
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self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
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self._new_member = False
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# Read a chunk of data from the file
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buf = self.fileobj.read(size)
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# If the EOF has been reached, flush the decompression object
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# and mark this object as finished.
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if buf == b"":
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uncompress = self.decompress.flush()
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self._read_eof()
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self._add_read_data( uncompress )
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raise EOFError('Reached EOF')
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uncompress = self.decompress.decompress(buf)
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self._add_read_data( uncompress )
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if self.decompress.unused_data != b"":
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# Ending case: we've come to the end of a member in the file,
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# so seek back to the start of the unused data, finish up
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# this member, and read a new gzip header.
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# (The number of bytes to seek back is the length of the unused
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# data, minus 8 because _read_eof() will rewind a further 8 bytes)
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self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)
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# Check the CRC and file size, and set the flag so we read
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# a new member on the next call
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self._read_eof()
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self._new_member = True
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def _add_read_data(self, data):
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self.crc = zlib.crc32(data, self.crc)
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self.extrabuf = self.extrabuf + data
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self.extrasize = self.extrasize + len(data)
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self.size = self.size + len(data)
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def _read_eof(self):
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# We've read to the end of the file, so we have to rewind in order
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# to reread the 8 bytes containing the CRC and the file size.
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# We check the that the computed CRC and size of the
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# uncompressed data matches the stored values. Note that the size
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# stored is the true file size mod 2**32.
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self.fileobj.seek(-8, 1)
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crc32 = read32(self.fileobj)
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isize = U32(read32(self.fileobj)) # may exceed 2GB
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if U32(crc32) != U32(self.crc):
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raise IOError("CRC check failed")
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elif isize != LOWU32(self.size):
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raise IOError("Incorrect length of data produced")
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def close(self):
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if self.mode == WRITE:
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self.fileobj.write(self.compress.flush())
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# The native zlib crc is an unsigned 32-bit integer, but
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# the Python wrapper implicitly casts that to a signed C
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# long. So, on a 32-bit box self.crc may "look negative",
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# while the same crc on a 64-bit box may "look positive".
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# To avoid irksome warnings from the `struct` module, force
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# it to look positive on all boxes.
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write32u(self.fileobj, LOWU32(self.crc))
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# self.size may exceed 2GB, or even 4GB
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write32u(self.fileobj, LOWU32(self.size))
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self.fileobj = None
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elif self.mode == READ:
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self.fileobj = None
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if self.myfileobj:
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self.myfileobj.close()
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self.myfileobj = None
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def __del__(self):
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try:
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if (self.myfileobj is None and
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self.fileobj is None):
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return
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except AttributeError:
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return
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self.close()
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def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH):
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if self.mode == WRITE:
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# Ensure the compressor's buffer is flushed
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self.fileobj.write(self.compress.flush(zlib_mode))
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self.fileobj.flush()
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def fileno(self):
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"""Invoke the underlying file object's fileno() method.
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This will raise AttributeError if the underlying file object
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doesn't support fileno().
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"""
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return self.fileobj.fileno()
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def isatty(self):
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return False
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def tell(self):
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return self.offset
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def rewind(self):
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'''Return the uncompressed stream file position indicator to the
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beginning of the file'''
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if self.mode != READ:
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raise IOError("Can't rewind in write mode")
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self.fileobj.seek(0)
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self._new_member = True
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self.extrabuf = b""
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self.extrasize = 0
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self.offset = 0
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def seek(self, offset, whence=0):
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if whence:
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if whence == 1:
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offset = self.offset + offset
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else:
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raise ValueError('Seek from end not supported')
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if self.mode == WRITE:
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if offset < self.offset:
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raise IOError('Negative seek in write mode')
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count = offset - self.offset
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chunk = bytes(1024)
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for i in range(count // 1024):
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self.write(chunk)
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self.write(bytes(count % 1024))
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elif self.mode == READ:
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if offset < self.offset:
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# for negative seek, rewind and do positive seek
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self.rewind()
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count = offset - self.offset
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for i in range(count // 1024):
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self.read(1024)
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self.read(count % 1024)
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def readline(self, size=-1):
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if size < 0:
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size = sys.maxint
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readsize = self.min_readsize
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else:
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readsize = size
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bufs = []
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while size != 0:
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c = self.read(readsize)
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i = c.find(b'\n')
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# We set i=size to break out of the loop under two
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# conditions: 1) there's no newline, and the chunk is
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# larger than size, or 2) there is a newline, but the
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# resulting line would be longer than 'size'.
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if (size <= i) or (i == -1 and len(c) > size):
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i = size - 1
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if i >= 0 or c == b'':
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bufs.append(c[:i + 1]) # Add portion of last chunk
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self._unread(c[i + 1:]) # Push back rest of chunk
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break
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# Append chunk to list, decrease 'size',
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bufs.append(c)
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size = size - len(c)
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readsize = min(size, readsize * 2)
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if readsize > self.min_readsize:
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self.min_readsize = min(readsize, self.min_readsize * 2, 512)
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return b''.join(bufs) # Return resulting line
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def readlines(self, sizehint=0):
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# Negative numbers result in reading all the lines
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if sizehint <= 0:
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sizehint = sys.maxint
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L = []
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while sizehint > 0:
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line = self.readline()
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if line == b"":
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break
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L.append(line)
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sizehint = sizehint - len(line)
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return L
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def writelines(self, L):
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for line in L:
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self.write(line)
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def __iter__(self):
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return self
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def __next__(self):
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line = self.readline()
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if line:
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return line
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else:
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raise StopIteration
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def _test():
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# Act like gzip; with -d, act like gunzip.
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# The input file is not deleted, however, nor are any other gzip
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# options or features supported.
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args = sys.argv[1:]
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decompress = args and args[0] == "-d"
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if decompress:
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args = args[1:]
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if not args:
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args = ["-"]
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for arg in args:
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if decompress:
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if arg == "-":
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f = GzipFile(filename="", mode="rb", fileobj=sys.stdin)
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g = sys.stdout
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else:
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if arg[-3:] != ".gz":
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print("filename doesn't end in .gz:", repr(arg))
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continue
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f = open(arg, "rb")
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g = builtins.open(arg[:-3], "wb")
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else:
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if arg == "-":
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f = sys.stdin
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g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)
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else:
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f = builtins.open(arg, "rb")
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g = open(arg + ".gz", "wb")
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while True:
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chunk = f.read(1024)
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if not chunk:
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break
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g.write(chunk)
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if g is not sys.stdout:
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g.close()
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if f is not sys.stdin:
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f.close()
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if __name__ == '__main__':
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_test()
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