inspect.stack() is slow.

[bckohan]

By default, if scope is not provided include() pulls the scope off the stack frame above the include() frame. It does this by calling inspect.stack(). This call does an enormous amount of unnecessary work. It builds frame info objects for the entire stack.

I noticed this on a production system that has some management commands that have shell tab completions. This means each time I hit tab, the entire Django stack is loaded. It was noticeably slow (~1.5 seconds). Profiling suggested 1/3 of that time was spent in inspect.stack(). This production system had roughly 20 calls to include() - to build the settings.

I removed all of that overhead by changing this line:

scope = scope or inspect.stack()[1][0].f_globals

To this:

scope = scope or sys._getframe(1).f_globals

I'll submit a PR.