Get uncompressed size of a .gz file in python

Question

Using gzip, tell() returns the offset in the uncompressed file.
In order to show a progress bar, I want to know the original (uncompressed) size of the file.
Is there an easy way to find out?

Answer 1

Uncompressed size is stored in the last 4 bytes of the gzip file. We can read the binary data and convert it to an int. (This will only work for files under 4GB)

import struct

def getuncompressedsize(filename):
    with open(filename, 'rb') as f:
        f.seek(-4, 2)
        return struct.unpack('I', f.read(4))[0]