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Using Docopt to Create CLI Documentation

This post will demonstrate how to use docopt in Python code to create CLI documentation. Docopt is a tool for creating and presenting documentation for command-line functions and scripts. Finally, we will demonstrate what the help documentation looks like at the command line.

The example code we’ll use is a reverse string function. The function itself is simple: It takes a string as input and returns it in reverse order. When invoked, the user is prompted to type a string, followed by the enter key. The reversed string will then be returned.

The implementation of docopt will be broken down into four steps:

  1. Install docopt
  2. Import docopt into Python
  3. Add help documentation as a docstring
  4. Implement docopt in the main function

At the end of this post, you’ll see the completed implementation.

Step One: Install docopt

To install docopt for Python at the command line, use the command below. We’ll use pip, Python’s standard package manager.

pip install docopt

Step Two: Import docopt

Open the reverse_string_with_docopt.py file and add an import statement above the function:

from docopt import docopt

Step Three: Add Help Documentation

Add the following Python docstring to the beginning of the file, before the import statement. The docstring contains sections for usage and options. The usage section defines how to invoke the function with arguments and options, while the options section specifies the available long and short options.

"""
Reverse String
Reverses any input string.

Usage: 
    reverse_string.py [reverse]
    reverse_string.py -h | --help
    reverse_string.py -v | --verbose

Options:
    -h --help      Show this
    -v --verbose   Verbose mode
    -q --quiet     Quiet mode
"""

In the usage section, ‘reverse’ will invoke the function. The options ‘-h’, ‘-v’, and ‘-q’ will return help information in various formats.

Step Four: Implement docopt

Add a main function to specify how the function and help documentation will be invoked. The arguments variable will receive the arguments passed from the command prompt, and the if/else block will execute the code based on the argument provided.

if __name__ == '__main__':
    arguments = docopt(__doc__)

    if arguments['reverse']:
        string_to_reverse = input('Enter the string to be reversed: ')
        reverse(string_to_reverse)
    else:
        print(arguments)

The argument is provided at the command line immediately after the Python script’s name. The __doc__ parameter could be a docstring or another string that contains a help message to be parsed.

The Complete Script

Here is the complete Python script, which you can also download from GitHub.

"""
Reverse String Function
Reverses any input string.

Usage:
    reverse_string.py [reverse]
    reverse_string.py -h | --help
    reverse_string.py -v | --verbose

Options:
    -h --help      Show this
    -v --verbose   Verbose mode
    -q --quiet     Quiet mode
"""
from docopt import docopt

def reverse(string_to_reverse):
    reversed_str = string_to_reverse[::-1]
    print(reversed_str)

if __name__ == '__main__':
    arguments = docopt(__doc__)

    if arguments['reverse']:
        string_to_reverse = input('Enter the string to be reversed: ')
        reverse(string_to_reverse)
    else:
        print(arguments)

Demo Usage

To execute the code, navigate to the directory where the file is located or use the complete path to the file. The command below will invoke the function without displaying help documentation.

python reverse_string_with_docopt.py reverse

You will be prompted to enter the string to be reversed.

To view the reverse function’s help documentation, use the options -h or --help.

python reverse_string_with_docopt.py -h

The result will display the help documentation added to the top of the file. When -q is invoked, it shows which option was used.

{'--help': False,
 '--quiet': True,
 '--verbose': False,
 'reverse': False}

Conclusion

This simple example demonstrates how to install and implement docopt with Python. There are other variants for C++, Go, Ruby, and more. Visit GitHub to view all variants. It’s important to note that CLI documentation isn’t a replacement for standalone documentation like a webpage or PDF.

Feel free to let me know if you need any further tweaks or improvements!

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