Python read from command line arguments or stdin

Question

When writing text-oriented command line programs in Python, I often want to read either all the files passed on the command line, or (XOR) standard input (like Unix cat does, or Perl's <>). So, I say

if len(args) == 0:  # result from optparse
    input = sys.stdin
else:
    input = itertools.chain(*(open(a) for a in args))

Is this the Pythonic way of doing this, or did my miss some part of the library?

Answer 1

You need fileinput.

A standard use case is:

import fileinput
for line in fileinput.input():
  process(line)

Answer 2

In Python 3, argparse handles filetype objects very nicely. It's an extremely powerful module and the docs come with many examples, so it's easy to quickly write the code you want. (How Pythonic!)

You may also benefit from this StackOverflow question about using argparse to optionally read from stdin.

Answer 3

See

How do you read from stdin in Python?