Try gzipping some data through the gzip libary like this...
import gzip
content = "Lots of content here"
f = gzip.open('Onlyfinnaly.log.gz', 'wb')
f.write(content)
f.close()
... then run your code as posted ...
import gzip
f=gzip.open('Onlyfinnaly.log.gz','rb')
file_content=f.read()
print file_content
This method worked for me as for some reason the gzip library fails to read some files.