[Python-Dev] Re: opcode performance measurements

[Samuele Pedroni]

From: Jeremy Hylton <jeremy@alum.mit.edu>
> >>>>> "SP" == Samuele Pedroni <pedronis@bluewin.ch> writes:
> 
>   SP> Hi. Q about PEP 267 Does the PEP mechanims adress only
>   SP> import a
>   SP> use a.x
> 
>   SP> cases. How does it handle things like
>   SP> import a.b
>   SP> use a.b.x
> 
> You're a smart guy, can you tell me?  :-).  Seriously, I haven't
> gotten that far.
> 
> import mod.sub
> creates a binding for "mod" in the global namespace
> 
> The compiler can detect that the import statement is a package import
> -- and mark "mod.sub" as a candidate for optimization.  A use of
> "mod.sub.attr" in function should be treated just as "mod.attr".
> 
> The globals array (dict-list hybrid, technically) has the publicly
> visible binding for "mod" but also has an internal binding for
> "mod.sub" and "mod.sub.attr".  Every module or submodule attribute in
> a function gets an internal slot in the globals.  The internal slot
> gets initialized the first time it is used and then shared by all the
> functions in the module.
> 
> So I think this case isn't special enough to need a special case.
> 

 OK, I stated the wrong question.  What happens if I do the following:

import a.b

def f():
   print a.b.x
   a.g()
   print a.b.x

f()

Now a.g() change a.b from a submodule to an object with a x attribute.
Maybe this case does not make sense, but the point is that the PEP
is quite vague about imported stuff.

Samuele (more puzzled than smart).