How to run a Python program from the command line

Introduction

Python is a versatile programming language that can be executed in various ways, including directly from the command line. This tutorial will guide you through the process of running Python programs from the command line, exploring the benefits and practical applications of this approach.

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Introduction to Python Command Line Execution

Python is a versatile programming language that can be executed in various ways, including through the command line interface (CLI). The command line, also known as the terminal or console, provides a text-based environment where users can interact with the operating system and run Python scripts directly.

Understanding the fundamentals of Python command line execution is essential for developers who want to automate tasks, run scripts, or integrate Python with other tools and workflows.

What is the Python Command Line?

The Python command line, or Python interpreter, is a tool that allows you to execute Python code directly in the terminal. It provides a REPL (Read-Eval-Print Loop) environment, where you can type in Python statements, and the interpreter will immediately evaluate and display the results.

The Python command line is a powerful tool for:

• Quickly testing and experimenting with Python code
• Executing small, one-off scripts
• Exploring the Python standard library and third-party modules
• Troubleshooting and debugging Python applications

Accessing the Python Command Line

To access the Python command line, you can follow these steps:

1. Open the terminal or command prompt on your operating system.
2. Type python (or python3 on systems with both Python 2 and Python 3 installed) and press Enter.
3. You should see the Python prompt >>>, indicating that you are now in the Python REPL.

$ python
Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

From here, you can start typing Python code and see the results immediately.

Running Python Scripts from the Command Line

In addition to the Python command line REPL, you can also run Python scripts directly from the command line. This is a common way to execute Python programs, especially for larger, more complex applications.

Creating a Python Script

To run a Python script from the command line, you first need to create a Python file. Here's an example of a simple Python script named hello.py:

print("Hello, LabEx!")

Executing a Python Script

Once you have created your Python script, you can run it from the command line using the following syntax:

$ python hello.py
Hello, LabEx!

Here's how it works:

1. Open the terminal or command prompt.
2. Navigate to the directory where your hello.py file is located.
3. Type python hello.py and press Enter.
4. The Python interpreter will execute the code in the hello.py file and display the output.

Command Line Arguments

You can also pass command line arguments to your Python script. These arguments can be accessed within the script using the sys.argv list. Here's an example:

import sys

if len(sys.argv) > 1:
    name = sys.argv[1]
else:
    name = "LabEx"

print(f"Hello, {name}!")

To run this script with a command line argument:

$ python hello.py World
Hello, World!

In this example, the script checks if any command line arguments were provided. If so, it uses the first argument as the name to greet. If no arguments are provided, it uses the default name "LabEx".

Benefits of Command Line Python Execution

Running Python scripts from the command line offers several benefits that make it a valuable tool for developers and system administrators. Let's explore some of the key advantages:

Automation and Scripting

The command line is particularly useful for automating repetitive tasks and creating scripts. By writing Python scripts and executing them from the command line, you can automate various workflows, such as file management, data processing, system administration, and more. This can save you a significant amount of time and effort.

Portability and Deployment

Python scripts can be easily shared and executed on different systems, as long as Python is installed. This makes command line Python execution a great choice for deploying applications or scripts to production environments, such as servers or cloud infrastructure.

Debugging and Troubleshooting

The command line provides a direct and interactive way to test and debug Python code. You can quickly run small snippets of code, explore the behavior of modules and libraries, and troubleshoot issues without the need for a full-fledged IDE.

Integration with Other Tools

The command line allows you to integrate Python with other command-line tools and utilities. You can, for example, use Python scripts to process the output of shell commands, automate system tasks, or even create custom command-line tools and utilities.

Reduced Resource Usage

Running Python scripts from the command line can be more resource-efficient compared to launching a full-blown Python environment or IDE. This makes it a suitable choice for executing lightweight scripts or performing quick tasks on systems with limited resources, such as embedded devices or low-powered servers.

By understanding the benefits of command line Python execution, you can leverage this powerful feature to streamline your development workflows, automate tasks, and create more efficient and versatile Python-based solutions.

Summary

By the end of this tutorial, you will have a solid understanding of how to run Python programs directly from the command line. You will learn the necessary steps, explore the advantages of this method, and be equipped to incorporate command line execution into your Python development workflow.