Skip to content

Instantly share code, notes, and snippets.

@martinth
Created August 6, 2015 11:04
Show Gist options
  • Save martinth/ed991fb8cdcac3dfadf7 to your computer and use it in GitHub Desktop.
Save martinth/ed991fb8cdcac3dfadf7 to your computer and use it in GitHub Desktop.
Read from stdin or files in Python (combining argparse and fileinput)
import argpase
import fileinput
if __name__ == '__main__':
parser = ArgumentParser()
parser.add_argument('--dummy', help='dummy argument')
parser.add_argument('files', metavar='FILE', nargs='*', help='files to read, if empty, stdin is used')
args = parser.parse_args()
# If you would call fileinput.input() without files it would try to process all arguments.
# We pass '-' as only file when argparse got no files which will cause fileinput to read from stdin
for line in fileinput.input(files=args.files if len(args.files) > 0 else ('-', )):
print(line)
@drmull
Copy link

drmull commented Nov 18, 2016

I found your snippet helpful. But I found out you don't need the if case though, just fileinput.input(args.files) will do, no arguments will make args.files an empty list and and an empty list will make fileinput read from stdin

@andylshort
Copy link

This really helps if any of your python3 scripts are suffering from a BrokenPipeError or are not being properly handled when you're piping input into a python script you wrote!

@mhashizume
Copy link

Thank you, both this and @drmull's comment were very helpful

@jsf80238
Copy link

Thank you, both this and @drmull's comment were very helpful.

@pinzyte
Copy link

pinzyte commented Dec 31, 2022

In the special case where only 1 file (or none for stdin) is allowed, use: nargs='?', default=[].

The default= is generally required or the default will be None, which will cause fileinput to think it needs to read from sys.argv. This is a problem if you have options on the command line as it will then try to open them as files, and you'll get errors like No such file or directory: '-a'.

Passing an empty array (which is what nargs='*' does when no files are specified) avoids this.

@fish8
Copy link

fish8 commented Aug 10, 2024

Thank you, both this and @drmull's comment were very helpful

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment