How to read from stdin or from a file if no data is piped in Python?

Question

I have a CLI script and want it to read data from a file. It should be able to read it in two ways :

• cat data.txt | ./my_script.py
• ./my

Answer 1

Argparse allows this to be done in a fairly easy manner, and you really should be using it instead of optparse unless you have compatibility issues.

The code would go something like this:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--input', type = argparse.FileType('r'), default = '-')

Now you have a parser that will parse your command line arguments, use a file if it sees one, or use standard input if it doesn't.