In the first and the second parts of this series we explored the ideas behind the execution and the compilation of a Python program. We'll continue to focus on ideas in the next parts but this time we'll make an exception and look at the actual code that brings those ideas to life.

In the first post of the series we've looked at the CPython VM. We've learned that it works by executing a series of instructions called bytecode. We've also seen that Python bytecode is not sufficient to fully describe what a piece of code does. That's why there exists a notion of a code object. To execute a code block such as a module or a function means to execute a corresponding code object. A code object contains block's bytecode, constants and names of variables used in the block and block's various properties.

Typically, a Python programmer doesn't write bytecode and doesn't create the code objects but writes a normal Python code. So CPython must be able to create a code object from a source code. This job is done by the CPython compiler. In this part we'll explore how it works.

Have you ever wondered what python does when you run one of your programs?

$ python script.py

This article opens a series which seeks to answer this very question.