The gzip Module

The gzip module allows you to read and write gzip-compressed files as if they were ordinary files, as shown in Example 5-24.

Example 5-24. Using the gzip Module to Read a Compressed File

File: gzip-example-1.py

import gzip

file = gzip.GzipFile("samples/sample.gz")

print file.read()

Well it certainly looks as though we're in for
a splendid afternoon's sport in this the 127th
Upperclass Twit of the Year Show.

The standard implementation doesn't support the seek and tell methods. Example 5-25 shows how to add forward seeking.

Example 5-25. Extending the gzip Module to Support seek/tell

File: gzip-example-2.py

import gzip

class gzipFile(gzip.GzipFile):
 # adds seek/tell support to GzipFile

 offset = 0

 def read(self, size=None):
 data = gzip.GzipFile.read(self, size)
 self.offset = self.offset + len(data)
 return data

 def seek(self, offset, whence=0):
 # figure out new position (we can only seek forwards)
 if whence == 0:
 position = offset
 elif whence == 1:
 position = self.offset + offset
 else:
 raise IOError, "Illegal argument"
 if position < self.offset:
 raise IOError, "Cannot seek backwards"

 # skip forward, in 16k blocks
 while position > self.offset:
 if not self.read(min(position - self.offset, 16384)):
 break

 def tell(self):
 return self.offset

#
# try it

file = gzipFile("samples/sample.gz")
file.seek(80)

print file.read()

this the 127th
Upperclass Twit of the Year Show.