Professional Python

Chapter 12CLI Tools

Python applications come in all sorts of flavors, including desktop applications, server-side applications, scripts, scientific computing applications, and much more.

Some Python applications must function with the command-line interface (CLI). They may need to ask for input, and receive arguments that are provided when the script is invoked.

This chapter examines optparse and argparse, the two tools that the Python standard library provides for writing applications that are run from the CLI.

OPTPARSE

optparse is the older of the two modules provided by Python, and is nominally considered to be deprecated as of Python 2.7 (when argparse was introduced). However, optparse is still very widely used, and is necessary for any code intended to support Python 2.6, which is still quite common in the Python ecosystem.

Essentially, optparse exists to provide a clear and consistent way to read arguments off of the command line, including positional arguments, as well as options and switches.

A Simple Argument

optparse is actually quite easy to understand once you look at an example. Consider the ­following simple Python script that takes an option from the CLI:

import optparse
if __name__ == '__main__':
    parser = optparse.OptionParser()
    options, args = parser.parse_args()
    print(' '.join(args).upper())

This script takes any number of arguments it receives, converts them to all capital letters, and prints them back out to the CLI.

$ python echo_upper.py $ python echo_upper.py ...