Python Internals

Dict & Set Internals

CPython's dict is a compact, insertion-ordered open-addressing hash table giving average O(1) lookup — and set is the very same machinery with the values removed.

Reference Counting & Garbage Collection

CPython frees most objects the instant their last reference goes away via reference counting, and a generational cyclic garbage collector mops up the reference cycles that counting alone can never reclaim.

The Global Interpreter Lock (GIL)

The GIL is a mutex in CPython that lets only one thread execute Python bytecode at a time — the single most misunderstood part of Python concurrency.