Docopt module in Python

In Python, the Docopt module is used to create command line interfaces. Similar to other command line parameters and options, docopt allows us to define command line parameters and options and generate help messages and usage strings for the program. In this article, we will learn how to define the Docopt module and how to use it to create a command line interface.

Install

Before use, you can install the Docopt module using the pip command in Python. To install the Docopt module, enter the following command on the terminal or command prompt.

pip install docopt

Programs using the Docopt module

After installing the Docopt module, let’s look at some examples to understand how to use the Docopt module in Python.

Example 1: Simple program

In the code below, we will provide the filename parameter 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 parameter 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 accepts a file name as an argument and an optional flag that specifies whether to display line numbers. We will use Docopt to define the command line interface. In the following example, we will provide the filename parameter 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 parameter 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

in conclusion

In this article, we discussed how to use the docopt module to create a command line interface and how to use it to create command line arguments and options. Its declarative approach makes it easy to define command line parameters and options, making it easy to use and understand. Using Docopt, you can quickly create command line interfaces for your Python programs without worrying about the details of argument parsing and help message generation.

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