Rename files

In the folder ”.\my_folder\subfolder\subsubfolder" there are files named:

• fileA_1.txt
• fileA_11.txt
• fileA_13.txt

I want to rename them changing A to B:

import os, glob
import re
file_path = os.path.abspath('my_folder//subfolder\subsubfolder/fileA_*.txt')
prev = 'file'
after = '_\d+\.txt$'
old = 'A'
new = 'B'

mach_string = '(?<={}){}(?={})'.format(prev, old, after)
for single_file in glob.glob(file_path):
    os.rename(single_file, re.sub(mach_string, new, single_file))

os.path.abspath is used to normalize the path (independently of the OS).

glob.glob returns the list af all file paths matching the input string.

A(?=_\d+\.txt$) looks for a A that preceeds a string of the type “_##ANY_NUMBER##.txt”.

(?<=file)A checks that A is preceeded by the string “file”.