Sort input from pipe or files on command line

natural_sort.py

#!/usr/bin/env python3

import re, sys

def natural_sort_key(s, _nsre=re.compile('([0-9]+)')):
    return [int(text) if text.isdigit() else text.lower()
            for text in re.split(_nsre, s)]    

fs = [sys.stdin] if not sys.stdin.isatty() else [open(fn) for fn in sys.argv[1:]]
for f in fs:
	for line in sorted(f, key=natural_sort_key):
		print(line, end='')