commas

#!/usr/bin/env python3

# Read a number from STDIN, and insert underscores into it.

# Author: Matt Post (@mjpost)

import sys

def main(args):
    for line in sys.stdin:
        num = line.strip()
        # Insert commas into the number.
        num = insert_commas(num, args.separator)

        # Print the number.
        print(num)

def insert_commas(prefix, separator):
    # Insert commas into the number.
    # First, reverse the number.
    if "." in prefix:
      prefix, suffix = prefix.split('.')
      suffix = f".{suffix}"
    else:
      suffix = ""

    prefix = prefix[::-1]
    # Next, insert commas every three characters.
    prefix = separator.join(prefix[i:i+3] for i in range(0, len(prefix), 3))
    # Finally, reverse the number again.
    prefix = prefix[::-1]
    # Return the number.

    return prefix + suffix

if __name__ == '__main__':
    import argparse
    parser = argparse.ArgumentParser(description='Insert commas into a number.')
    parser.add_argument('--separator', '-s', default='_', help='Separator to use (default: "_")')
    args = parser.parse_args()

    main(args)