Parsing command-line arguments

In this section, we are going to learn about parsing arguments and the module used to parse arguments.

Command-line arguments in Python

We can start a program with additional arguments, in the command line. Python programs can start with command-line arguments. Let's look at an example:

$ python program_name.py img.jpg

Here, program_name.py and img.jpg are arguments.

Now, we are going to use modules to get the arguments:

Module	Use	Python version
optparse	Deprecated	< 2.7
sys	All arguments in sys.argv (basic)	All
argparse	Building a command-line interface	>= 2.3
fire	Automatically generating Command-Line Interfaces (CLIs)	All
docopt	Creating CLIs interfaces	>= 2.5

Sys.argv

The sys module is used to access command-line parameters. The len(sys.argv) function contains the number of arguments. To print all of the arguments, simply execute str(sys.argv). Let's have a look at an example:

01.py
import sys
print('Number of arguments:', len(sys.argv))
print('Argument list:', str(sys.argv))

Output:
Python3 01.py img
Number of arguments 2
Arguments list: ['01.py', 'img']