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synced 2025-11-04 03:44:55 +00:00
95bdd0b604
1. Jack Jansen reports that on the Mac, the time may be negative, and solves this by adding a write32u() function that writes an unsigned long. 2. On 64-bit platforms the CRC comparison fails; I've fixed this by casting both values to be compared to "unsigned long" i.e. modulo 0x100000000L.
333 lines
11 KiB
Python
333 lines
11 KiB
Python
import time
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import string
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import zlib
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import struct
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import __builtin__
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# implements a python function that reads and writes a gzipped file
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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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FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
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READ, WRITE = 1, 2
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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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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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return GzipFile(filename, mode, compresslevel)
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class GzipFile:
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myfileobj = None
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def __init__(self, filename=None, mode=None,
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compresslevel=9, fileobj=None):
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if fileobj is None:
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fileobj = self.myfileobj = __builtin__.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 = 1
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self.extrabuf = ""
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self.extrasize = 0
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self.filename = filename
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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 ValueError, "Mode " + mode + " not supported"
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self.fileobj = fileobj
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if self.mode == WRITE:
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self._write_gzip_header()
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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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if filename[-3:] != '.gz':
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filename = filename + '.gz'
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self.filename = 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('\037\213') # magic header
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self.fileobj.write('\010') # compression method
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fname = self.filename[:-3]
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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))
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write32u(self.fileobj, long(time.time()))
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self.fileobj.write('\002')
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self.fileobj.write('\377')
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if fname:
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self.fileobj.write(fname + '\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 != '\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 (1):
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s=self.fileobj.read(1)
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if not s or s=='\000': 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 (1):
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s=self.fileobj.read(1)
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if not s or s=='\000': 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.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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def writelines(self,lines):
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self.write(string.join(lines))
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def read(self, size=None):
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if self.extrasize <= 0 and self.fileobj is None:
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return ''
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readsize = 1024
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if not size: # get the whole thing
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try:
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while 1:
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self._read(readsize)
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readsize = 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 = 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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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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def _read(self, size=1024):
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if self.fileobj is None: 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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#
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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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self.fileobj = None
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return 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 = 0
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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 == "":
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uncompress = self.decompress.flush()
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self._read_eof()
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self.fileobj = None
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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 != "":
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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 = 1
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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.
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self.fileobj.seek(-8, 1)
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crc32 = read32(self.fileobj)
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isize = read32(self.fileobj)
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if crc32%0x100000000L != self.crc%0x100000000L:
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raise ValueError, "CRC check failed"
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elif isize != self.size:
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raise ValueError, "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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write32(self.fileobj, self.crc)
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write32(self.fileobj, 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 flush(self):
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self.fileobj.flush()
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def seek(self):
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raise IOError, 'Random access not allowed in gzip files'
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def tell(self):
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raise IOError, 'I won\'t tell() you for gzip files'
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def isatty(self):
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return 0
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def readline(self):
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bufs = []
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readsize = 100
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while 1:
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c = self.read(readsize)
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i = string.find(c, '\n')
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if i >= 0 or c == '':
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bufs.append(c[:i+1])
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self._unread(c[i+1:])
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return string.join(bufs, '')
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bufs.append(c)
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readsize = readsize * 2
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def readlines(self):
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buf = self.read()
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lines = string.split(buf, '\n')
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for i in range(len(lines)-1):
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lines[i] = lines[i] + '\n'
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if lines and not lines[-1]:
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del lines[-1]
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return lines
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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 _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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import sys
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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:", `arg`
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continue
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f = open(arg, "rb")
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g = __builtin__.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 = __builtin__.open(arg, "rb")
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g = open(arg + ".gz", "wb")
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while 1:
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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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