Question

I created two modules, one with

def _func():
    print "hi"

and another

def func():
    print "hi"

When I use the help function on the module including the first function, the help module doesn’t display this function. As opposed the second example where this function shows in the help output. Is there any functional difference aside from the use of the help function?

Answer 1

Yes, there is an (admittedly subtle) difference functionality-wise. Let’s assume you have a module A.py:

foo = 1
_bar = 2

Observe:

>>> from A import *
>>> foo
1
>>> _bar
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name '_bar' is not defined

The default behaviour if you do an import * is that members with a leading underscore are not imported. You can override that behaviour by specifying an __all__ list:

__all__ = ['foo', '_bar']

foo = 1
_bar = 2

Now:

>>> from A import *
>>> (foo, _bar)
(1, 2)

By the way, __all__ also overrides the list of members shown by help() or pydoc:

$ pydoc A | cat
 ...
DATA
    __all__ = ['foo', '_bar']
    _bar = 2
    foo = 1
 ...