I've seen some Python code whose __init__.py file has a __all__ variable with a list assigned.
Example:
__all__ = ['foo', 'bar']
I've noticed that in Python, when things start with underline , it means that it's some special functionality.
So, I'd like to know what this __all__ is for?
__all__ must be a list of strings that defines which symbols are exported from a module when from <module> import * is used.
It also serves to make it easier to read the code. Anyone reading the source code will easily know which members are publicly exposed to this module.
Module code
__all__ = ['foo', 'bar']
baz = 5
bar = 10
def foo():
return 'qualquer coisa'
In use
from module import *
print foo()
print bar
# A linha abaixo causará uma exception, porque o membro não foi exportado
print baz
I put the code in GitHub for future reference
If the __all__ of the above example is removed, all members whose name does not start with underline will be imported.
Note : It is important to note that members cited in __all__ will only affect the behavior of import * . Therefore, members not listed in it remain accessible by " import direct". In the example, it would be possible to from modulo import baz and use this value.