Can someone explain __all__ in Python?

Question

I have been using Python more and more, and I keep seeing the variable __all__ set in different __init__.py files. Can someone explain what this d

Answer 1

Short answer

__all__ affects from import * statements.

Long answer

Consider this example:

foo
├── bar.py
└── __init__.py

In foo/__init__.py:

• (Implicit) If we don't define __all__, then from foo import * will only import names defined in foo/__init__.py.

• (Explicit) If we define __all__ = [], then from foo import * will import nothing.

• (Explicit) If we define __all__ = [ , ... ], then from foo import * will only import those names.

Note that in the implicit case, python won't import names starting with _. However, you can force importing such names using __all__.

You can view the Python document here.