__all__ and 'from module import *'

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Accepted Answer

When you do 'from mymodule import *', Python checks for __all__. If __all__ exists, only those names are imported - even if other names exist in the module. Without __all__, Python falls back to importing every name that does not start with an underscore, which can pollute the caller's namespace with internal helpers. Defining __all__ is the clean way to publish a module's public API. Think of it as the equivalent of 'public' in a statically typed language. For libraries, always define __all__ so downstream users aren't surprised by what 'import *' drags in.