[Python-Dev] Fast access to builtins (original) (raw)

Raymond Hettinger python@rcn.com
Fri, 28 Mar 2003 05:58:44 -0500

[GvR]

Hi Raymond. Too bad you couldn't make it to the conference! We're all having a great time on and off the GWU premises.

Glad you guys are having a great time. I wish I could be there.

I used your "more zen" on a slide in my keynote.

Cool. Any chance of getting your keynote slides on the net?

> From past rumblings, I gather that Python is moving > towards preventing builtins from being shadowed.

You must be misunderstanding. The only thing I want to forbid is to stick a name in another module's globals that would shadow a builtin.

Yes, that is different.
Allowing shadows means having to watch out for trees.

The idea of forbidding module B in the first example is that the optimizer is allowed to replace len(a) with a bytecode that calls PyOjectSize() rather than looking up "len" in globals and builtins. The optimizer should only be allowed to make this assumption if careful analysis of an entire module doesn't reveal any possibility that "len" can be shadowed . . . BTW this idea is quite old; I've described it a few years ago under a subject something like "low-hanging fruit".

The fruit is a bit high. Doing a full module analysis means deferring the optimization for a second pass after all the code has already been generated. It's doable, but much harder.

def f(x): return len(x) + 10 # knowing whether to optimize this

def g(): global len # when this is allowed len = lambda x: 5 # is a bear

The task is much simpler if it can be known in advance that the substitution is allowed (i.e. a module level switch like: fastbuiltins = True).

Raymond Hettinger