Recursive Python Function Example: Make a List of Your Movies!

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

Let’s make a list of all video files 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:

def factorial(n):
    if n == 0:
        return 1
    else:
        return n * factorial(n - 1)

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

• Python Programming – Recursion
• How to Recursively Copy a Folder (Directory) in Python
• Python Programming – Date and Time Functions

Recursive Python Function: Let’s Code!

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

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)

The code is pretty much self-explanatory along with the comments. The recursive Python function print_movie_files takes two arguments: the directory path to search. Then it gets a list of all files and folders in this directory using the os.listdir method. We use a for loop to work on the list,, check whether the filepath is a normal 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 further process it.

Calling the Recursive Python Function

Now, we call this function within the __main__ scope:

Python 3.x

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 <CTRL-C>
    try:
        input()
    except KeyboardInterrupt:
        exit(0)

Python 2.x

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 <CTRL-C>
    try:
        raw_input()
    except KeyboardInterrupt:
        exit(0)

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.