Swapping One File Extension for Another Throughout a Directory Tree

Problem

You need to rename files throughout a subtree of directories, specifically changing the names of all files with a given extension so that they have a different extension instead.

Solution

Operating on all files of a whole subtree of directories is easy enough with the os.walk function from Python's standard library:

 1>>> import os
 2>>> def swapextensions(dir, before, after):
 3    if before[:1] != '.':
 4        before = '.'+before
 5    length = -len(before)
 6    if after[:1] != '.':
 7        after = '.'+after
 8    for path, dirs, files in os.walk(dir):
 9        for oldfile in files:
            if oldfile[length:] == before:
                oldfile = os.path.join(path, oldfile)
                newfile = oldfile[:length] + after
                os.rename(oldfile, newfile)

 

Usage

Before swap:

>>> for path, dirs, files in os.walk('c:\\Test'):
    for f in files:
        print f

        
3545.csv
abc.txt
e.xml

 

Swap:

>>> swapextensions('c:\\Test', 'txt', 'csv')

 

After swap:

>>> for path, dirs, files in os.walk('c:\\Test'):
    for f in files:
        print f

        
3545.csv
abc.csv
e.xml