Understanding How Python Code Works: From Script to Execution

Posted by Afsal on 07-Jun-2024

Hi Pythonistas!

Welcome to another exciting dive into the world of Python! Today, we’re going to explore the journey of a simple Python program from code to execution. Buckle up as we unravel the magic that happens behind the scenes when you run a Python script.

Writing the Code

Let's start with a basic example. Suppose we have a script that greets a user by their name:

def greet(name):
    return f"Hello, {name}!"

if __name__ == "__main__":
    user_name = "Pythonista"

Interpreting the Code

Python is an interpreted language, meaning it reads and executes code line by line. Here’s what happens step-by-step:


The interpreter first reads the code to check for syntax errors. If everything looks good, it moves on to the next step.

Compiling to Bytecode:

The code is compiled into bytecode, a low-level, platform-independent representation of your source code. This bytecode is what gets executed by the Python Virtual Machine (PVM).

Executing Bytecode:

The PVM takes over and executes the bytecode. This is where the actual work happens, translating bytecode into actions performed by your computer.

Running the Code

To see our greeting in action, we run the script from the command line:

python greeting.py
  • When you execute this command, the following sequence unfolds:
  • The interpreter starts by checking the script for any syntax errors.
  • If the script is error-free, it gets compiled into bytecode.
  • The bytecode is executed by the PVM.


Hello Pythonistas

Key Components of Python Execution

Python Interpreter: The main program that reads and executes Python code.

Parser: Converts source code into a format that can be understood by the compiler.

Compiler: Converts the parsed code into bytecode.

Python Virtual Machine (PVM): Executes the bytecode.

Understanding how Python code works behind the scenes helps you write better and more efficient code. From parsing and compiling to bytecode execution, each step is crucial in transforming your Python script into actions performed by your computer.