google-python-style

Place imports at the top of the file in four groups: __future__ imports, standard library, third-party packages, then repository sub-packages. Sort each group lexicographically by full package path, use one import per line, and never use relative imports.

Use module_name, ClassName, function_name, GLOBAL_CONSTANT_NAME, and instance_var_name patterns. Avoid single-character names except for counters and iterators, avoid double-underscore privacy, and never use dashes in .py filenames.

Annotate public APIs at minimum, plus code that is error-prone, hard to understand, or type-stable. Declare None explicitly with X | None in Python 3.10+, and prefer abstract container types like collections.abc.Sequence over concrete list in signatures.

Mutable default values are evaluated once at definition time and shared across calls, causing state to leak between invocations. The Google style guide prohibits them; use None as the default and assign the mutable object inside the function body.

It is a style reference, not a beginner tutorial, and it does not teach Python fundamentals. Repository-specific requirements and newer authoritative guidance take precedence over these rules when they conflict.