OS.Walk and Fnmatch in Python


In an earlier post, OS.walk in Python, I described how to use os.walk and showed some examples on how to use it in scripts.

In this article, I will show how to use the os.walk() module function to walk a directory tree, and the fnmatch module for matching file names.

What is OS.walk?

It generates the file names in a directory tree by walking the tree either top-down or bottom-up.

For each directory in the tree rooted at directory top (including top itself), it yields a 3-tuple (dirpath, dirnames, filenames).

dirpath # is a string, the path to the directory.

dirnames # is a list of the names of the subdirectories in dirpath (excluding ‘.’ and ‘..’).

filenames # is a list of the names of the non-directory files in dirpath.

Note that the names in the lists contain no path components.

To get a full path (which begins with top) to a file or directory in dirpath, do os.path.join(dirpath, name). For more information, please see the Python Docs.

What is Fnmatch

The fnmatch module compares file names against glob-style patterns such as used by Unix shells.

These are not the same as the more sophisticated regular expression rules. It’s purely a string matching operation.

If you find it more convenient to use a different pattern style, for example regular expressions, then simply use regex operations to match your filenames.

What does it do?

The fnmatch module is used for the wild-card pattern matching.

Simple Matching

fnmatch() compares a single file name against a pattern and returns a boolean indicating whether or not they match. The comparison is case-sensitive when the operating system uses a case-sensitive file system.


To test a sequence of filenames, you can use filter(). It returns a list of the names that match the pattern argument.

Find all mp3 files

This script will search for *.mp3 files from the rootPath (“/”)

import fnmatch
import os
rootPath = '/'
pattern = '*.mp3'
for root, dirs, files in os.walk(rootPath):
    for filename in fnmatch.filter(files, pattern):
        print( os.path.join(root, filename))

Search computer for specific files

This script uses ‘os.walk’ and ‘fnmatch’ with filters to search the hard-drive for all image files

import fnmatch
import os

images = ['*.jpg', '*.jpeg', '*.png', '*.tif', '*.tiff']
matches = []

for root, dirnames, filenames in os.walk("C:\"):
    for extensions in images:
        for filename in fnmatch.filter(filenames, extensions):
            matches.append(os.path.join(root, filename))

There are many other (and faster) ways to do this, but now you understand the basics of it.

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