Answer to http://stackoverflow.com/questions/6512131

replace.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import argparse
from os import path
import re

replacements = {}
pattern = '<<([^>]*)>>'


def user_replace(match):
    ## Pull from replacements dict or prompt
    placeholder = match.group(1)
    if placeholder in replacements:
        return replacements[placeholder]
    ## .setdefault(key, value) returns the value if present, else sets it then returns
    return replacements.setdefault(placeholder, raw_input('%s? ' % placeholder))


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('infile', type=argparse.FileType('r'))
    parser.add_argument('outfile', type=argparse.FileType('w'))
    args = parser.parse_args()

    matcher = re.compile(pattern)

    for line in args.infile:
        new_line = matcher.sub(user_replace, line)
        args.outfile.write(new_line)

    args.infile.close()
    args.outfile.close()

if __name__ == '__main__':
    main()