Python Command Line Arguments

Python Command line arguments are input parameters passed to the script when executing them. Almost all programming language provide support for command line arguments. Then we also have command line options to set some specific options for the program.

Python Command Line Arguments

There are many options to read python command line arguments. The three most common ones are:

1. Python sys.argv
2. Python getopt module
3. Python argparse module

Let’s look through simple program to learn how to read and use python command line arguments.

Python sys module

Python sys module stores the command line arguments into a list, we can access it using sys.argv. This is very useful and simple way to read command line arguments as String. Let’s look at a simple example to read and print command line arguments using python sys module.

import sys

print(type(sys.argv))
print('The command line arguments are:')
for i in sys.argv:
    print(i)

Below image illustrates the output of a sample run of above program. There are many other useful functions in sys module, read them in detail at python sys module.

Python getopt module

Python getopt module is very similar in working as the C getopt() function for parsing command-line parameters. Python getopt module is useful in parsing command line arguments where we want user to enter some options too. Let’s look at a simple example to understand this.

import getopt
import sys

argv = sys.argv[1:]
try:
    opts, args = getopt.getopt(argv, 'hm:d', ['help', 'my_file='])
    print(opts)
    print(args)
except getopt.GetoptError:
    # Print a message or do something useful
    print('Something went wrong!')
    sys.exit(2)

Above example is very simple, but we can easily extend it to do various things. For example, if help option is passed then print some user friendly message and exit. Here getopt module will automatically parse the option value and map them. Below image shows a sample run. To learn more, read python getopt module.

Python argparse module

Python argparse module is the preferred way to parse command line arguments. It provides a lot of option such as positional arguments, default value for arguments, help message, specifying data type of argument etc. At the very simplest form, we can use it like below.

import argparse

parser = argparse.ArgumentParser()
parser.parse_args()

Below is the output from quick run of above script. Python argparse module provide a lot many features, you should read about them at python argparse tutorial for clear understanding. That’s all for different options to read and parse command line arguments in python, you should decide which is the one for your specific requirements and then use it. References:

• sys.argv
• getopt module
• argparse module