rename.py

import os
import re

PATH = os.path.abspath(os.path.dirname(__file__))


def rename(n):
    if n <= 0:
        return

    for root, _, files in os.walk(PATH, topdown=True):
        for f in files:
            if re.match(r"\d+\.\w+", f):
                index = f.find(".")

                if index == n:
                    continue
                elif n > index:
                    filename = f[:index].zfill(n) + f[index:]
                else:
                    filename = f[:index][-n:] + f[index:]

                filename = os.path.join(root, filename)

                if os.path.exists(filename):
                    os.remove(filename)

                os.rename(os.path.join(root, f), filename)


if __name__ == "__main__":
    rename(4)