All 15 Modules & Packaging questions
More in Modules & Packaging
How does Python's module import system avoid re-executing a module multiple times when imported from different places? What is the difference between an absolute import and a relative import within a package? What does the `if __name__ == '__main__':` idiom accomplish, and why is it important for modules? How does pyproject.toml serve as the modern standard for defining a Python package's build configuration and dependencies? What is the purpose of a `requirements.txt` file, and how does it differ from dependency declarations in pyproject.toml? What does 'editable install' (pip install -e .) mean, and why is it useful during development? How does Python locate modules during import, and what is sys.path's role? What is a namespace package, and how does it differ from a regular package? How does Python resolve circular imports, and what strategies avoid the resulting ImportError? How does importlib let you dynamically import a module by name at runtime?
Advertisement
Python › Modules & Packaging

What is __all__ and how does it control `from module import *` behavior?

Intermediate

Answer

__all__ is a list of strings defined at module level specifying exactly which names are exported when a client does `from module import *`. Without __all__, `import *` imports all public names (those not starting with an underscore); with __all__ defined, only the listed names are imported, giving the module author explicit control over its public API surface.
# mymodule.py
__all__ = ['public_func', 'PublicClass']

def public_func(): pass
def _private_helper(): pass
class PublicClass: pass

# from mymodule import *  only imports public_func and PublicClass
Real-world example A utility module defines __all__ to explicitly exclude internal helper functions from wildcard imports, keeping the importing namespace clean and preventing accidental use of implementation details.

Common follow-ups: Does __all__ affect explicit `from module import _private`?;Why is `import *` generally discouraged regardless?

Modules & Packaging;Functions & Scope
All 15 Modules & Packaging questions