How to tell if a file is gzip compressed?

Question

I have a Python program which is going to take text files as input. However, some of these files may be gzip compressed.

Is there a cross-platform, usable from Py

Answer 1

As of python3.7, this works

import gzip
with gzip.open(input_file, 'r') as fh:
    try:
        fh.read(1)
    except OSError:
        print('input_file is not a valid gzip file by OSError')

As of python3.8, this also works:

import gzip
with gzip.open(input_file, 'r') as fh:
    try:
        fh.read(1)
    except gzip.BadGzipFile:
        print('input_file is not a valid gzip file by BadGzipFile')