[Python-Dev] Fast access to __builtins__

[M.-A. Lemburg]

Raymond Hettinger wrote:
>>From past rumblings, I gather that Python is moving
> towards preventing __builtins__ from being shadowed.
> 
> I would like to know what you guys think about going ahead 
> with that idea whenever the -O optimization flag is set.
> 
> The idea is to scan the code for lines like:
> 
>     LOAD_GLOBAL  2 (range)
> 
> 
> and, if the name is found in __builtins__, then lookup
> the name, add the reference to the constants table and, 
> replace the code with something like:
> 
>    LOAD_CONST   5 (<type 'range'>)

Using the -O for this is not a working possibility. -OO
is reserved for optimizations which can change semantics,
but even there, I'd rather like a per-module switch than
a command line switch.

BTW, why not have a new opcode for symbols in the
builtins and then only tweak the opcode implementation
instead of having the compiler generate different code ?

> The opcode replacement bypasses module level shadowing 
> but leaves local shadowing intact.  For example:
> 
> modglob = 1            
> range = xrange 
> def f(list):
>      for i in list:         # local shadowing of 'list' is unaffected
>           print ord(i)    # access to 'ord' is optimized
>           j = modglob  # non-shadowed globals are unaffected
>           k = range(j)   # shadowing of globals is ignored
> 
> 
> I've already tried out a pure python proof-of-concept and it is 
> straightforward to recode it in C and attach it to PyCode_New().  
> 
> 
> Raymond Hettinger
> 
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-- 
Marc-Andre Lemburg
eGenix.com

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