why does dead code costs time?

Bruno Dupuis python.ml.bruno.dupuis at lisael.org
Wed Dec 5 19:24:13 CET 2012


On Wed, Dec 05, 2012 at 10:59:26AM -0700, Ian Kelly wrote:
> On Wed, Dec 5, 2012 at 10:34 AM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info> wrote:
> > The difference is almost certain between the LOAD_CONST and the
> > LOAD_GLOBAL.
> >
> > As to *why* there is such a difference, I believe that's a leftover from
> > early Python days when None was not a keyword and could be reassigned.
> 
> I think this should even be considered a bug, not just a missing
> optimization.  Consider:

This is definitely a bug

> >>> globals()['None'] = 42
> >>> def f(x):
> ...     return None
> ...     print(x)
> ...
> >>> f('test')
> 42

This one is pretty scary

The difference between `return None` and `return` leads to inconsistency and
is in contradiction with the specs, AFAIK. I'm glad we pointed this out.

-- 
Bruno Dupuis



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