[Python-ideas] 'Injecting' objects as function-local constants

[Alex Light]

On Tue, Jun 14, 2011 at 5:27 PM, Jan Kaliszewski <zuo at chopin.edu.pl> wrote:

> Alex Light dixit (2011-06-14, 13:44):
>
> > >>>            frmglobals = func.__globals__.copy()
> > >>>            func.__globals__.update(localArgs)
> > >>>            ret= func(*args, **kwargs)
> > >>>            func.__globals__.clear()
> > >>>            func.__globals__.update(frmglobals)
>
> Changing global state on each call seems to be both
> concurrency-and-recurrency-unsafe and inefficient.
>

well some of your safety concerns can be allayed, i hope, by replacing this
snipet:

>>>            frmglobals = func.__globals__.copy()
>>>            func.__globals__.update(localArgs)
>>>            ret= func(*args, **kwargs)
>>>            func.__globals__.clear()
>>>            func.__globals__.update(frmglobals)

with this one:

>>>            with _modifyGlobals(func.__globals__, localArgs):
>>>                ret = func(*args, **kwargs)

with  _modifyGlobals defined as:

>>>from contextlib import contextmanager
>>>
>>>@contextmanager
>>>def _modifyGlobals(glbls, additions):
>>>    frmglbls = glbls.copy()
>>>    try:
>>>        glbls.update(additions)
>>>        yield
>>>    finally:
>>>        glbls.clear()
>>>        glbls.update(frmglbls)

as for performance you are correct that it is more efficient to just use
global variables.
the dictionary updates add about 1 x 10**-4 (or, if the check for collisions
with KWargs is removed, 5 x 10**-5)
seconds  to the run time of a function, at least on this computer.
so not terribly significant just be sure to use sparingly

also with the link you mentioned i could not seem to get it to work.
Whenever i tried to use any built-in functions
it would start throwing NameErrors. also that is only useful if you want to
inject all global variables into the function.

--Alex
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