Recursion Example — Walking a file tree

Many developers use Python as a platform independent scripting language to perform file system operations. Sometimes it’s necessary to walk through a file system. Here is one way to navigate a file system recusively. (Of course, Python has libaries that do this!)

import os

def walk_fs(start_dir):
    # Get a list of everything in start_dir
    contents = os.listdir(start_dir)

    # This stores the output
    output = []

    # Loop through every item in contents
    for f in contents:
        # Use os.path.join to reassmble the path
        f_path = os.path.join(start_dir, f)

    # check if f_path is directory (or folder)
    if os.path.isdir(f_path):
        # Make recusive call to walk_fs
        output = output + walk_fs(f_path)
        # Add the file to output

    # Return a list of files in the directory
    return output

if __name__ == '__main__':
        result = walk_fs(input('Enter starting folder => '))
        for r in result:
    except FileNotFoundError:
    print('Not a valid folder! Try again!')

The key to this is to begin by using os.listdir, which returns a list of every item in a directory. Then we can loop through each item in contents. As we loop through contents, we need to reassemble the full path because f is only the name of the file or directory. We use os.path.join because it will insert either / (unix-like systems) or \ (windows) between each part of the path.

The next statement checks if f_path is a file or directory. The os.path.isdir function is True if the item is a directory, false otherwise. If f_path is a folder, we can make a recursive call to walk_fs starting with f_path. It will return a list of files that we can concat to output.

If f_path is a file, we just add it to output. When we have finished iterating through contents, we can return output. The output file will hold all of the files in start_dir and it’s subdirectorys.


3 thoughts on “Recursion Example — Walking a file tree”

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: