__all__ = ['bar', 'baz']

waz = 5
bar = 10
def baz(): return 'baz'

from foo import *

print bar
print baz

# The following will trigger an exception, as "waz" is not exported by the module
print waz

__all__ = ['foo', 'Bar']

from module import *               # imports foo and Bar

package/
   |-__init__.py # makes directory a Python package
   |-module_1.py
   |-module_2.py

from module_1 import *
from module_2 import *

__all__ = ['foo',]

__all__ = ['Bar',]

import package
package.foo()
package.Bar()

package/
   |-__init__.py
   |-module_1/
   |  |-__init__.py
   |  |-foo_implementation.py
   |-module_2/
      |-__init__.py
      |-Bar_implementation.py

from foo_implementation import *
__all__ = ['foo']

from Bar_implementation import *
__all__ = ['Bar']

from Bar_implementation import *
from Baz_implementation import *
__all__ = ['Bar', 'Baz']

from module_1 import *       # also constrained by __all__'s
from module_2 import *       # in the __init__.py's
__all__ = ['foo', 'Bar']     # further constraining the names advertised

import package
package.Baz()

from module_1 import *
from module_2 import *
__all__ = ['foo', 'Bar', 'Baz']

import os as _os, sys as _sys

import sys

def export(fn):
    mod = sys.modules[fn.__module__]
    if hasattr(mod, '__all__'):
        mod.__all__.append(fn.__name__)
    else:
        mod.__all__ = [fn.__name__]
    return fn

$ cat > main.py
from lib import export
__all__ = [] # optional - we create a list if __all__ is not there.

@export
def foo(): pass

@export
def bar():
    'bar'

def main():
    print('main')

if __name__ == '__main__':
    main()

$ cat > run.py
import main
main.main()

$ python run.py
main

$ cat > run.py
from main import *
foo()
bar()
main() # expected to error here, not exported

$ python run.py
Traceback (most recent call last):
  File "run.py", line 4, in <module>
    main() # expected to error here, not exported
NameError: name 'main' is not defined

a = "A"
b = "B"
c = "C"

__all__ = ['a', 'b']

a = "A"
b = "B"
c = "C"

__all__

__all__

""" cheese.py """

__all__ = ['swiss', 'cheddar']

swiss = 4.99
cheddar = 3.99
gouda = 10.99

>>> from cheese import *
>>> swiss, cheddar
(4.99, 3.99)
>>> gouda
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'gouda' is not defined

>>> import cheese
>>> cheese.swiss, cheese.cheddar, cheese.gouda
(4.99, 3.99, 10.99)

>>> from cheese import swiss, cheddar, gouda
>>> swiss, cheddar, gouda
(4.99, 3.99, 10.99)

>>> import cheese as ch
>>> ch.swiss, ch.cheddar, ch.gouda
(4.99, 3.99, 10.99)

__all__ = [
    'MySQLConnection', 'Connect', 'custom_error_exception',

    # Some useful constants
    'FieldType', 'FieldFlag', 'ClientFlag', 'CharacterSet', 'RefreshOption',
    'HAVE_CEXT',

    # Error handling
    'Error', 'Warning',

    ...etc...

    ]

foo
├── bar.py
└── __init__.py