Docopt module in Python

Docopt module in Python is used to create command-line interfaces. Similar to other command line arguments and options docopt allows us to define command line arguments and options and also generate help messages and usage strings for the Program. In this article, we will understand how the Docopt module is defined and how it is used to create a command line interface.

Installation

You can install the Docopt module before using it with the help of the pip command in Python. To install the Docopt module type the following command on your terminal or command prompt.

pip install docopt

Programs to use the Docopt module

After installing the Docopt module let’s see some examples to see how to use the Docopt module in Python.

Example 1: Simple Program

In the following code we will provide the filename argument when running the program. For example, if the program file is simple_program.py and we have a test.txt file in the same directory then the argument should be python simple_program.py test.txt.

""" Usage: simple_program.py <filename>

Print the contents of the file to the console.
"""

from docopt import docopt

def main():
   args = docopt(__doc__)
   filename = args['<filename>']
   with open(filename, 'r') as f:
      print(f.read())

if __name__ == '__main__':
   main()

Output

This is testing the docopt module.

Example 2: Program with options

In this example, we will create a program that takes a filename as an argument and an optional flag that specifies whether or not to display line numbers. We will define the command-line interface using Docopt. In the following example, we will provide the filename argument and the –line-numbers flag when running the program. For example, if the program file is simple_program.py and we have a test.txt file in the same directory then the argument should be python simple_program.py test.txt –line-numbers.

"""Usage: program_with_options.py [--line-numbers] <filename>

Print the contents of the file to the console, with line numbers if specified.

Options:
  --line-numbers  Display line numbers.
"""

from docopt import docopt

def main():
   args = docopt(__doc__)
   filename = args['<filename>']
   with open(filename, 'r') as f:
      if args['--line-numbers']:
         for i, line in enumerate(f):
            print(f"{i+1}: {line}", end="")
      else:
         print(f.read())

if __name__ == '__main__':
    main()

Output

1: This is testing the docopt module.
2: This is line 2
3: This is line 3
4: This is line 4

Conclusion

In this article, we discussed how the docopt module is used to create command-line interfaces and how it can be used to create command-line arguments and options. Its declarative approach to defining command-line arguments and options makes it easy to use and understand. With Docopt, you can quickly create command-line interfaces for your Python programs without having to worry about the details of argument parsing and help message generation.