Python Controlling Exports

Following is from David Beazley's talk.

Each submodule in a package can define __all__.

# spam/foo.py

__all__ = [ 'Foo' ]

class Foo:
    ...

# spam/bar.py

__all__ = [ 'Bar' ]

class Bar:
    ...

# spam/__init__.py

from .foo import Foo
from .bar import Bar

__all__ = (foo.__all__ + bar.__all__)

This is used in the standard library (eg. in asyncio)