Python - Add leading 0 to file numbers

Question

I am new to python and programming generally I have 1200 text files in a folder, in the following format:
James - 1 - How to... .txt
Sarah - 2 - How to... .txt
Steph - 3 - How to... .txt
...
Mariah - 200 - How to... .txt
...
Rashford - 1200 - How to... .txt

I want to rename the files below 1000 to add leading 0's so they all have the same number of digits, for instance, 0001, 0050, 0300

This is my code so far, but am stuck:

#!python3

import os
from tkinter import filedialog

cleaned_files = []

root_folder = filedialog.askdirectory()
os.chdir(root_folder)
folder_files = os.listdir(root_folder)

# Filter out files starting with '.' and '_'
cleaned_files = []
for item in folder_files:
    if item[0] == '.' or item[0] == '_':
        pass
    else:
        cleaned_files.append(item)


# Find file names of the root folder and save them


def getFiles(files):
    for file in files:
        file_start, file_number, file_end = file.split('-')
        file_number.strip()

        # Was trying to append just one 0 to numbers <10
        if int(file_number) < 10:
            print(file_number)
        else:
            pass
getFiles(cleaned_files)

Answer 1

As you were said in comments, str.zfill is one possible and simple solution.

You have just to change your getfiles function:

def getFiles(files):
    for file in files:
        file_start, file_number, file_end = file.split('-')
        num = file_number.split().zfill(4)  # num is 4 characters long with leading 0

        new_file = "{}- {} -{}".format(file_start, num, file_end)
        # rename or store the new file name for later rename

Answer 2

Modify your append method like this (mentioned by @gtlambert and @zondo):

    # Was trying to append just one 0 to numbers <10
    file_number.zfill(4)

Python string zfill