rename_files.py

#!/usr/bin/env python3

import os
import re
import sys


def get_new_path(path):
    # find the number in the filename, looks like "#5"
    filename = os.path.basename(path)

    match = re.search(r'#(\d+)', filename)
    if not match:
        return None

    number = match.group(1)

    # make this operation idempotent
    # i.e. if the output already starts with the number prefix, don't prepend
    number_prefix = '{} - '.format(number)
    if filename.startswith(number_prefix):
        return None

    output_filename = '{}{}'.format(number_prefix, filename)
    output_path = os.path.join(os.path.dirname(path), output_filename)
    return output_path


def rename_file(path):
    new_path = get_new_path(path)
    if not new_path:
        print("Not renaming '{}'".format(path))
        return  # don't rename
    else:
        print("Renaming '{}' to '{}'".format(path, new_path))
        os.rename(path, new_path)


if __name__ == '__main__':
    """take a list of files as input and rename the files"""

    files = sys.argv[1:]
    for file in files:
        rename_file(file)