[dmorgan]

>Yes there is lookup, always lookup. Dynamic language, something in loop could change what lstr is.

And why is that presented as something inevitable?

The interpreter/compiler could analyze that part and see that the function/name is not changed during the loop, and cache for that.

I'd guess that PyPy tries to do it that way, anyway...

[lvh]

Yes, that's one of the many optimizations PyPy does, however it's only a very limited one. PyPy goes much, much deeper than this, with tools like function inlining and escape analysis.