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How Python Works

Beginner Satellite

How Python Works

Python source files become bytecode that runs on a virtual machine. Understanding that flow helps you debug imports, performance, and packaging issues later.

See compiled vs interpretedRun scripts confidently

Execution pipeline​

  1. Source code (.py) is read by the interpreter.
  2. Python compiles it to bytecode (.pyc files in __pycache__).
  3. Bytecode runs on the Python Virtual Machine (PVM).

This compilation step happens automatically; you don't manage it manually.

CPython vs others​

  • CPython: default implementation, written in C.
  • PyPy: JIT-compiled, faster for long-running programs.
  • MicroPython / CircuitPython: embedded devices.

The language spec stays consistent, but performance characteristics vary.

Import mechanism recap​

When you import module, Python:

  1. Checks sys.modules cache.
  2. Searches paths in sys.path.
  3. Loads source/bytecode and executes the module once.

Understanding this explains why top-level code runs on import and why circular imports cause issues.

Memory model​

  • Python uses reference counting with a cycle detector.
  • Objects live on the heap; names reference them.
  • gc module lets you inspect or tweak garbage collection behavior, but defaults suffice for most apps.

Next up in your learning path

Compare compiled vs interpreted

Clarify terminology and tradeoffs.

Concept

Learn how to run scripts

Use python CLI flags + shebangs.

Practical

Explore the REPL

Interactively inspect bytecode and objects.

Hands-on