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Last Updated: Wednesday 29th December 2021
This recipe is a practical example of Python recursive functions, using the `os.listdir` function. However it is not the most effective method to traverse a directory in Python. `os.walk` is generally considered the most Pythonic method. For a quick look at how to use `os.walk`, checkout the article this article for a os.walk example. If you are after a more in-depth look at `os.walk`, be sure to checkout the article Python's os.walk: An In-depth Guide

So. What's better than making a list of video files on your hard disc drive?

Let's make a list of all video filesÂ in a folder, and all other folders in it!

## What is a Recursive Function in Python?

Recursion is a concept in computer science. Essentially, it divides a problem into sub-problems. Recursion in Python generally relates to a specific function, method or object, which calls itself to break up these problems. For example, a factorial function would be as follows:

[python]
def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)
[/python]

Note that the `factorial` function calls itself, to break down the factorial problem into sub-problems.

## Recursive Python Function: Let's Code!

Let's write the code of traversal within a function, which looks like:

[python]
import os

def print_movie_files(movie_directory, movie_extensions=['avi', 'dat', 'mp4', 'mkv', 'vob']):
''' Print files in movie_directory with extensions in movie_extensions, recursively. '''

# Get the absolute path of the movie_directory parameter
movie_directory = os.path.abspath(movie_directory)

# Get a list of files in movie_directory
movie_directory_files = os.listdir(movie_directory)

# Traverse through all files
for filename in movie_directory_files:
filepath = os.path.join(movie_directory, filename)

# Check if it's a normal file or directory
if os.path.isfile(filepath):

# Check if the file has an extension of typical video files
for movie_extension in movie_extensions:
# Not a movie file, ignore
if not filepath.endswith(movie_extension):
continue

# We have got a video file! Increment the counter
print_movie_files.counter += 1

# Print it's name
print('{0}'.format(filepath))
elif os.path.isdir(filepath):
# We got a directory, enter into it for further processing
print_movie_files(filepath)
[/python]

The code is pretty much self-explanatory along with the comments. The recursive Python function `print_movie_files` takes twoÂ arguments: the directory path to search. Then it gets a list of all files and folders in this directory usingÂ the `os.listdir` method. We use a `for` loop to work on the `list,`, check whether the filepath is a normalÂ file or directory using the `os.path.isfile` method. If it's a normal file with an extension in `movie_extensions`, it will print the filepath. If `filepath` is a directory, we recursively call the function itself to furtherÂ process it.

## Calling the Recursive Python Function

Now, we call this function within the `__main__` scope:

[python]
if __name__ == '__main__':

# Directory argument supplied, check and use if it's a directory
if len(sys.argv) == 2:
if os.path.isdir(sys.argv[1]):
movie_directory = sys.argv[1]
else:
print('ERROR: "{0}" is not a directory.'.format(sys.argv[1]))
exit(1)
else:
# Set our movie directory to the current working directory
movie_directory = os.getcwd()

print('\n -- Looking for movies in "{0}" --\n'.format(movie_directory))

# Set the number of processed files equal to zero
print_movie_files.counter = 0

# Start Processing
print_movie_files(movie_directory)

# We are done. Exit now.
print('\n -- {0} Movie File(s) found in directory {1} --'.format \
(print_movie_files.counter, movie_directory))
print('\nPress ENTER to exit!')

# Wait until the user presses enter/return, or
try:
input()
except KeyboardInterrupt:
exit(0)
[/python]

[python]
if __name__ == '__main__':

# Directory argument supplied, check and use if it's a directory
if len(sys.argv) == 2:
if os.path.isdir(sys.argv[1]):
movie_directory = sys.argv[1]
else:
print('ERROR: "{0}" is not a directory.'.format(sys.argv[1]))
exit(1)
else:
# Set our movie directory to the current working directory
movie_directory = os.getcwd()

print('\n -- Looking for movies in "{0}" --\n'.format(movie_directory))

# Set the number of processed files equal to zero
print_movie_files.counter = 0

# Start Processing
print_movie_files(movie_directory)

# We are done. Exit now.
print('\n -- {0} Movie File(s) found in directory {1} --'.format \
(print_movie_files.counter, movie_directory))
print('\nPress ENTER to exit!')

# Wait until the user presses enter/return, or
try:
raw_input()
except KeyboardInterrupt:
exit(0)
[/python]

## Running the Script

1. Download and extract the source code zip file (see below), and copy `list-movies.py` to the directory you wish to search in.
2. -- OR -- copy the article code to a new file and save it as `list-movies.py` in the directory you wish to search in.
3. `cd` into the directory the movies are in. eg. `cd ~/Movies` or `cd C:\\Users\\Videos`.
4. Run the `list-movies.py` script with `/path/to/python list-movies.py`
• Linux/OSX/Unix: `python list-movies.py`
• Windows: `C:\\Python34\\python.exe list-movies.py`

Tip: On Linux/OSX/Unix you can mark the file as executable, add a Python shebang line at the top of the file, and run it directly. eg.

[shell]
cd ~/Desktop/list-movies.py
chmod +x ./list-movies.py
# Add "#/usr/bin/env python" to the top of the file
./list-movies.py # Run script, search files in current directory
./list-movies.py ~/Movies # Run script, search for files in ~/Movies
[/shell]

The code in the script willÂ recursively traverse (look in) all other folders within it, and check for video files.Â If you're using Windows and have Python IDLE installed, you can just double-click on the file and check theÂ output.

Once again, the `os.getcwd` method helps us to get the current working directory (cwd), i.e. the directory where the script resides. It calls our just-written function and also has a counter, it counts how many video files itÂ found. Finally, we `print` all information we have, and wait for a prompt from the user to terminate theÂ program using the `input()` or `raw_input()` function (Python changed the name of the `raw_input()` function to `input()` when going from Python 2 to Python 3).