You wrote your python script. You hit "run." What happens next? It's not magic. Here's the breakdown.
1. You Write Code
You start with a text file, let's say my_script.py. This is your source code. It's human-readable. A computer has no idea what print("Hello") means directly.
2. The "Interpreter" Actually Compiles First
This is where people get confused. Python is called an "interpreted" language, but the first thing the Python program does is compile your source code.
What it does: It translates your .py script into a set of simpler, low-level instructions called bytecode.
The result: This bytecode is saved in a file with a .pyc extension, usually in a __pycache__ folder. You don't usually see this or need to touch it. Python handles it automatically.
Why? Running bytecode is much faster than re-reading and re-analyzing your plain English-like source code every single time.
So, is Python compiled? Yes, to bytecode. But it's not compiled all the way down to machine code like C++ or Java. That's the next step.
3. The Python Virtual Machine (PVM) Takes Over
This is the "runtime engine." It's the part that actually runs your code.
What it is: The PVM is a program that acts like a simplified, virtual computer. Its job is to understand and execute your bytecode.
How it works: The PVM reads the bytecode instructions from your .pyc file one by one and executes them. It translates these bytecode instructions into machine code that your computer's actual processor (CPU) can understand and run.
The big advantage: This PVM is what makes Python portable. You can run the same .py file on Windows, macOS, or Linux without changing it. As long as you have the right Python PVM installed on that machine, it will handle the final translation for that specific operating system.
The Whole Process, Simplified:
- You: Write my_script.py.
- Python Compiler: Translates my_script.py into my_script.pyc (bytecode). This happens automatically when you run the script.
- Python Virtual Machine (PVM): Takes my_script.pyc, reads the bytecode, and executes the instructions on your computer's hardware.
That's it. It's a two-step process of compilation to bytecode, followed by interpretation of that bytecode by the PVM. This gives Python a balance of performance and portability.