TIL - In Python __all__ Controls What Imports * Exposes

Defining __all__ in a module explicitly declares its public API. Without it, from module import * imports everything not starting with _. With it, only the listed names are exported.

# utils.py

__all__ = ["format_date", "parse_date"]

def format_date(d): ...
def parse_date(d): ...
def _internal_helper(): ... # not exported

Even if you never use import *, __all__ serves as documentation - it tells readers and IDEs what the public surface area is.