how to optionally handle and decompress gzipped input files on the fly with python

optionally-handle-gzip-files.py

#!/usr/bin/python

from __future__ import print_function
import gzip

class GZopen(object):
    def __init__(self, filename):
        f = open(filename)
        # the file type can be determined with the first 2 bytes
        magic_number = f.read(2)
        # rewind the file reader back to the start
        f.seek(0)

        if magic_number == '\x1f\x8b':
            self.f = gzip.GzipFile(fileobj=f)
        else:
            self.f = f

    # methods to use within 'with' blocks
    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        try:
            self.f.fileobj.close()
        except AttributeError:
            pass
        finally:
            self.f.close()

    # inteface used by python 'opened' files
    def __getattr__(self, name):
        return getattr(self.f, name)
    def __iter__(self):
        return iter(self.f)
    def next(self):
        return next(self.f)
        
        
if __name__ == '__main__':
    possible_gzipped_file = sys.argv[1]
    with GZopen(possible_gzipped_file) as f:
        for line in f:
            print(line.rstrip())