Importing empty symbol causes double initialization of some modules

[Grzegorz Lukasik <hauserx@…>]

In file templatetags/__init__.py there is a line:

__path__.extend(__import__(a + '.templatetags', {}, {}, ['']).__path__)

__import__ method as fourth parameters gets a list of symbols to import. If this list is empty, __import__ returns the top-level package, but if the list contains anything the specified package is returned as described in ​http://docs.python.org/lib/built-in-funcs.html . So in this file there is a hack where not empty list but list that contains 'something' is passed - list that contains single empty name.

But it causes some strange side-effects - the specified module is initialized twice. First with correct name and later with name followed by a dot (e.g. 'prog.app.templatetags' and 'prog.app.templatetags.'). In some cases it may cause serious problems.

[Grzegorz Lukasik <hauserx@…>]

patch based on description in ​http://docs.python.org/lib/built-in-funcs.html

[Grzegorz Lukasik <hauserx@…>]

Attached patch should be used, or at least some existing name instead of should be used ( like 'name' )

[Grzegorz Lukasik <hauserx@…>]

The same construction is used in few places in django.

[Grzegorz Lukasik <hauserx@…>]

simple python test illustrating the problem

[Grzegorz Lukasik <hauserx@…>]

simple django application that illustrates the problem

[Grzegorz Lukasik <hauserx@…>]

Description from submission on Python bug list: ​http://bugs.python.org/issue2090

{{{ ...it's a hack, so supporting an abuse of the API is not
reasonable. You don't have to set the fromlist for the import to work.
And if you are doing it to get the tail module, you can write some
simple code to use getattr() to walk down from the root module to the
one you want }}}

In the next two days I will prepare a patch that will resolve similar problems in other places in Django.