How Python Works

📘 Premium Read: Access my best content on Medium member-only articles — deep dives into Java, Spring Boot, Microservices, backend architecture, interview preparation, career advice, and industry-standard best practices.

✅ Some premium posts are free to read — no account needed. Follow me on Medium to stay updated and support my writing.

🎓 Top 10 Udemy Courses (Huge Discount): Explore My Udemy Courses — Learn through real-time, project-based development.

▶️ Subscribe to My YouTube Channel (172K+ subscribers): Java Guides on YouTube

Hey there, and welcome!

In this guide, we’re going to explore exactly how Python works — from the moment you write your code to the point it runs as a program on your machine.

Python is known for being easy to write and read, but under the hood, it goes through some pretty interesting steps before your code actually runs. In this lesson, we’ll walk through that entire journey, step by step, using a simple visual guide.

Let’s get started.

Step 1 – Writing the Code

We begin in the code editor — this is where you write your Python program.

You might be building a calculator, automating a task, or just printing "Hello, world!" — but once you’re done writing, you save your work as a Python source file.

This file ends with the extension dot P Y, or .py.

At this point, it’s just a plain text file with your code inside. The magic starts when we run that file through the Python system.

---

Step 2 – Compilation to Bytecode

When you run a Python file, something interesting happens in the background.

Python uses a compiler to take your code and translate it into bytecode — a lower-level version of your code that’s easier for a computer to work with.

This bytecode is saved in a file that ends in dot P Y C, or .pyc.

Now, it’s important to note that bytecode isn’t the same as machine code — your computer still doesn’t run this directly. Instead, it’s a kind of intermediate language that’s designed to be understood by something called the Python Virtual Machine.

---

Step 3 – The Python Virtual Machine

Once the bytecode is ready, it’s handed off to the PVM — short for Python Virtual Machine.

The PVM is like an interpreter that reads your bytecode and runs it line by line. It’s the engine behind the scenes that actually executes your code.

The virtual machine is part of what makes Python so flexible — because it creates a layer between your code and the operating system. That means your Python program can run on Windows, Mac, or Linux without needing to be rewritten.

So, your .py file becomes .pyc, then the PVM reads that and starts executing your program.

---

Step 4 – Libraries and Modules

As your program runs, it might use additional features — like math functions, file handling, or external tools.

These extra features come from libraries and modules, which Python loads in during execution.

Think of libraries like toolkits. Instead of writing everything from scratch, you can import powerful tools that save you time and simplify your code.

Python has thousands of these modules built-in or available online — for things like data analysis, web development, machine learning, and more.

And as shown in the diagram, these libraries feed into the process just before or during execution — giving your program extra functionality when needed.

---

Step 5 – Machine Code and Execution

Eventually, all of this — the bytecode, the virtual machine, the libraries — comes together to produce machine code.

This is the binary code — the ones and zeros — that your computer actually understands.

Behind the scenes, the Python interpreter takes care of translating your high-level code into machine-level instructions so the CPU can execute them.

And that’s the final step: your program runs. Maybe it prints a result, saves a file, or responds to user input — but now, it’s fully functional and running live.

---

Wrap-Up

So let’s quickly review how Python works:

• You start by writing your code in a code editor, and save it in a file that ends with dot P Y.
• When you run the program, Python compiles that file into bytecode, stored in a dot P Y C file.
• The Python Virtual Machine — or PVM — reads that bytecode and executes it line by line.
• Along the way, it uses any libraries or modules your program depends on.
• And finally, Python translates everything into machine code that your computer understands — and your program runs.

This entire process is handled for you automatically when you run a Python script. But now that you know what’s happening behind the scenes, you’ll understand why Python is such a powerful and flexible language.

Thanks for reading— and I’ll see you in the next lesson!