Adding Jeremy Hylton's gzip module.

This requires Andrew Kuchling's zlib extension module.
It still needs some doc strings.

Lib/gzip.py

+import time
+import string
+import zlib
+import StringIO
+
+# implements a python function that reads and writes a gzipped file
+# the user of the file doesn't have to worry about the compression,
+# but sequential access is not allowed
+
+# based on Andrew Kuchling's minigzip.py distributed with the zlib module
+
+FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
+
+READ, WRITE = 1, 2
+
+def write32(output, value):
+    t = divmod(value, 256)
+    b1 = chr(t[1])
+
+    t = divmod(t[0], 256)
+    b2 = chr(t[1])
+
+    t = divmod(t[0], 256)
+    b3 = chr(t[1])
+
+    t = divmod(t[0], 256)
+    b4 = chr(t[1])
+
+    buf = b1 + b2 + b3 + b4
+    output.write(buf)
+   
+    
+def read32(input):
+    buf = input.read(4)
+    v = ord(buf[0])
+    v = v + (ord(buf[1]) << 8)
+    v = v + (ord(buf[2]) << 16)
+    v = v + (ord(buf[3]) << 24)
+    return v
+
+written = []
+
+_py_open = open
+
+def open(filename, mode, compresslevel=9):
+    return GzipFile(filename, mode, compresslevel)
+
+class GzipFile:
+
+    def __init__(self, filename, mode='r', compresslevel=9):
+	if mode == 'r' or mode == 'rb':
+	    self.mode = READ
+	    self._init_read()
+	    self.filename = filename
+	    self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
+
+	elif mode == 'w' or mode == 'wb':
+	    self.mode = WRITE
+	    self._init_write(filename)
+	    self.compress = zlib.compressobj(compresslevel,
+					     zlib.DEFLATED, 
+					     -zlib.MAX_WBITS,
+					     zlib.DEF_MEM_LEVEL,
+					     0)
+	else:
+	    raise ValueError, "Mode " + mode + " not supported"
+
+	self.fileobj = _py_open(self.filename,mode)
+
+	if self.mode == WRITE:
+	    self._write_gzip_header()
+	elif self.mode == READ:
+	    self._read_gzip_header()
+	    
+
+    def __repr__(self):
+	s = repr(self.fileobj)
+	return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'
+
+    def _init_write(self, filename):
+	if filename[-3:] != '.gz':
+	    filename = filename + '.gz'
+	self.filename = filename
+	self.crc = zlib.crc32("")
+	self.size = 0
+	self.writebuf = []
+	self.bufsize = 0
+
+    def _write_gzip_header(self):
+	self.fileobj.write('\037\213')             # magic header
+	self.fileobj.write('\010')                 # compression method
+	self.fileobj.write(chr(FNAME))
+	write32(self.fileobj, int(time.time()))
+	self.fileobj.write('\002')
+	self.fileobj.write('\377')
+	self.fileobj.write(self.filename[:-3] + '\000')
+
+    def _init_read(self):
+	self.crc = zlib.crc32("")
+	self.size = 0
+	self.extrabuf = ""
+	self.extrasize = 0
+
+    def _read_gzip_header(self):
+	magic = self.fileobj.read(2)
+	if magic != '\037\213':
+	    raise RuntimeError, 'Not a gzipped file'
+	method = ord( self.fileobj.read(1) )
+	if method != 8:
+	    raise RuntimeError, 'Unknown compression method'
+	flag = ord( self.fileobj.read(1) )
+	# modtime = self.fileobj.read(4)
+	# extraflag = self.fileobj.read(1)
+	# os = self.fileobj.read(1)
+	self.fileobj.read(6)
+
+	if flag & FEXTRA:
+	    # Read & discard the extra field, if present
+	    xlen=ord(self.fileobj.read(1))		
+	    xlen=xlen+256*ord(self.fileobj.read(1))
+	    self.fileobj.read(xlen)
+	if flag & FNAME:
+	    # Read and discard a null-terminated string containing the filename
+	    while (1):
+		s=self.fileobj.read(1)
+		if s=='\000': break
+	if flag & FCOMMENT:
+	    # Read and discard a null-terminated string containing a comment
+	    while (1):
+		s=self.fileobj.read(1)
+		if s=='\000': break
+	if flag & FHCRC:
+	    self.fileobj.read(2)     # Read & discard the 16-bit header CRC
+
+
+    def write(self,data):
+	if len(data) > 0:
+	    self.size = self.size + len(data)
+	    self.crc = zlib.crc32(data, self.crc)
+	    self.fileobj.write( self.compress.compress(data) )
+
+    def writelines(self,lines):
+	self.write(string.join(lines))
+
+    def read(self,size=None):
+	if self.extrasize <= 0 and self.fileobj.closed:
+	    return ''
+	
+	if not size:
+	    # get the whole thing
+	    try:
+		while 1:
+		    self._read()
+	    except EOFError:
+		size = self.extrasize
+	else:
+	    # just get some more of it
+	    try:
+		while size > self.extrasize:
+		    self._read()
+	    except EOFError:
+		pass
+	
+	chunk = self.extrabuf[:size]
+	self.extrabuf = self.extrabuf[size:]
+	self.extrasize = self.extrasize - size
+
+	return chunk
+
+    def _read(self):
+	buf = self.fileobj.read(1024)
+	if buf == "":
+	    uncompress = self.decompress.flush()
+	    if uncompress == "":
+		self._read_eof()
+		self.fileobj.close()
+		raise EOFError, 'Reached EOF'
+	else:
+	    uncompress = self.decompress.decompress(buf)
+	self.crc = zlib.crc32(uncompress, self.crc)
+	self.extrabuf = self.extrabuf + uncompress
+	self.extrasize = self.extrasize + len(uncompress)
+	self.size = self.size + len(uncompress)
+
+    def _read_eof(self):
+	# Andrew writes:
+	## We've read to the end of the file, so we have to rewind in order
+	## to reread the 8 bytes containing the CRC and the file size.  The
+	## decompressor is smart and knows when to stop, so feeding it
+	## extra data is harmless.  
+	self.fileobj.seek(-8, 2)
+	crc32 = read32(self.fileobj)
+	isize = read32(self.fileobj)
+	if crc32 != self.crc:
+	    self.error = "CRC check failed"
+	elif isize != self.size:
+	    self.error = "Incorrect length of data produced"
+
+    def close(self):
+	if self.mode == WRITE:
+	    self.fileobj.write(self.compress.flush())
+	    write32(self.fileobj, self.crc)
+	    write32(self.fileobj, self.size)
+	    self.fileobj.close()
+	elif self.mode == READ:
+	    self.fileobj.close()
+
+    def flush(self):
+	self.fileobj.flush()
+
+    def seek(self):
+	raise IOError, 'Random access not allowed in gzip files'
+
+    def tell(self):
+	raise IOError, 'I won\'t tell() you for gzip files'
+
+    def isatty(self):
+	return 0
+
+    def readline(self):
+	# should I bother with this
+	raise RuntimeError, "not implemented"
+
+    def readlines(self):
+	# should I bother with this
+	raise RuntimeError, "not implemented"
+
+    
+class StringIOgz(GzipFile):
+
+    """A StringIO substitute that reads/writes gzipped buffers."""
+
+    def __init__(self, buf=None, filename="StringIOgz"):
+	"""Read/write mode depends on first argument.
+
+	If __init__ is passed a buffer, it will treat that as the
+	gzipped data and set up the StringIO for reading. Without the
+	initial argument, it will assume a new file for writing.
+
+	The filename argument is written in the header of buffers
+	opened for writing. Not sure that this is useful, but the
+	GzipFile code expects *some* filename."""
+
+	if buf:
+	    self.mode = READ
+	    self._init_read()
+	    self.filename = filename
+	    self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
+	    self.fileobj = StringIO.StringIO(buf)
+	else:
+	    self.mode = WRITE
+	    self._init_write(filename)
+	    self.compress = zlib.compressobj(compresslevel,
+					     zlib.DEFLATED, 
+					     -zlib.MAX_WBITS,
+					     zlib.DEF_MEM_LEVEL,
+					     0)
+	    self.fileobj = StringIO.StringIO()
+
+	if self.mode == WRITE:
+	    self._write_gzip_header()
+	elif self.mode == READ:
+	    self._read_gzip_header()
+