python - Read from File, or STDIN

Question

I've written a command line utility that uses getopt for parsing arguments given on the command line. I would also like to have a filename be an optional argument, such as it is in other utilities like grep, cut etc. So, I would like it to have the following usage

tool -d character -f integer [filename]

How can I implement the following?

• if a filename is given, read from the file.
• if a filename is not given, read from STDIN.

Answer 1

The fileinput module may do what you want - assuming the non-option arguments are in args then:

import fileinput
for line in fileinput.input(args):
    print line

If args is empty then fileinput.input() will read from stdin; otherwise it reads from each file in turn, in a similar manner to Perl's while(<>).