Unzip gz file if necessary

unzip_if_necessary.py

 def unzip_if_necessary(self, filename):
        print "unzip_if_necessary: " + filename
        f = open(filename)

        # Read magic number (the first 2 bytes) and rewind.                                                                                                                                                                               
        magic_number = f.read(2)
        f.seek(0)
        f.close()

        if magic_number == '\x1f\x8b':
            print "gzip file"
            data = ''
            # with  gzip.GzipFile(fileobj=f) as f:                                                                                                                                                                                        
            with gzip.open(filename, 'rb') as f:
                data = f.read()
            print "Writing to " + filename
            with open(filename, "w") as f:
                f.write(data)
        else:
            print "csv file"