Python tarfile error - gzip module not available

Question

I have the following code

import tarfile

for archive in archives:
    tar = tarfile.open(archive, "r:gz")
    tar.extractall()
    tar.close()

where archives is list of files with .tar.gz extension. Although it crashes while trying to open tar.gz file with tarfile.CompressionError: gzip module is not available. It is interesting, because module gzip.py is located in /usr/lib/python2.6.

When I try command file <name_of_archive> it returns: <name_of_archive>: gzip compressed data, from Unix.

How can I solve this?

Thanks