Day 5 - Command Line Args and Environment Variables in Python

Introduction:

Welcome to Day 5 of our Python journey! In this article, we'll explore a fundamental aspect of Python programming: handling command-line arguments and environment variables. These are essential tools for building versatile and configurable applications. Let's break it down step by step.

Step 1: Setting the Stage

Before diving into command line arguments and environment variables, make sure you have Python installed on your system. You can download Python from the official website (python.org).

Step 2: What Are Command Line Arguments?

Command line arguments are parameters passed to a Python script when it's executed from the terminal. These arguments allow you to customize the behavior of your script without modifying its source code.

Here's how you can access command line arguments:

import sys

# Get the script name
script_name = sys.argv[0]

# Get additional command line arguments
arguments = sys.argv[1:]

Step 3: Parsing Command Line Arguments

To make command-line argument handling more user-friendly, you can use libraries like argparse. This library simplifies argument parsing, provides help messages, and enforces argument types.

import argparse

parser = argparse.ArgumentParser(description="A simple Python script with command line arguments.")
parser.add_argument("--input", help="Input file")
parser.add_argument("--output", help="Output file")
args = parser.parse_args()

input_file = args.input
output_file = args.output

Step 4: Environment Variables

Environment variables are global variables that can be accessed by all processes running on your system. Python allows you to access and manipulate environment variables easily using the os module.

To access an environment variable:

import os

my_variable = os.environ.get("MY_VARIABLE")

Step 5: Setting Environment Variables

You can also set environment variables within your Python script:

import os

os.environ["MY_VARIABLE"] = "Hello, World!"

Step 6: Running Your Python Script

Now, let's put it all together. Save your Python script (let's call it script.py) with the command line argument and environment variable code we discussed.

To run your script with command line arguments:

python script.py --input input.txt --output output.txt

To access an environment variable in your script:

import os

my_variable = os.environ.get("MY_VARIABLE")
print(my_variable)

Step 7: Conclusion

In this article, we've covered the basics of working with command-line arguments and environment variables in Python. These concepts are crucial for building versatile and configurable applications that can adapt to different scenarios.

As you continue your Python journey, you'll find many use cases for command-line arguments and environment variables, from creating user-friendly command-line tools to configuring application settings.

Keep exploring and experimenting, and in no time, you'll become a Python pro. Happy coding!