Python

CPython's LazyImport Implementation in C

Oct 20, 2026 10 min read Jay Hubbert

Lazy imports work by parking a proxy object in the namespace and atomically replacing it with the real module the first time the name is touched.

Python Cpython Internals Lazy import Import

CPython's list Implementation in C

Oct 20, 2026 7 min read Jay Hubbert

CPython’s list is a contiguous array of pointers with a separate size and capacity, growing by about an eighth each time so appends stay O(1) amortized.

Python Cpython Internals List

CPython's memoryview Implementation in C

Oct 20, 2026 9 min read Jay Hubbert

CPython splits memoryview into a shared managed-buffer snapshot and a per-view copy of shape/strides, so slicing adjusts pointers instead of copying data.

Python Cpython Internals Memoryview Buffer protocol

CPython's Module Implementation in C

Oct 20, 2026 8 min read Jay Hubbert

Every Python module is, at the C level, an instance of PyModule_Type. Unlike bool or int, a module is a mutable object whose “attributes” are just the entries of its dictionary. …

Python Cpython Internals Module

CPython's NoneType Implementation in C (None)

Oct 20, 2026 6 min read Jay Hubbert

None is Python’s “no value” sentinel. There is exactly one instance of NoneType, it is immortal, it has no methods, and comparing it is just pointer equality. In CPython all of …

Python Cpython Internals Nonetype None