Op 2005-02-05, Nick Coghlan schreef <[EMAIL PROTECTED]>:
[ ... ]
With a rebinding operator, the intent of the last line can be made explicit:
def collapse(iterable): it = iter(iterable) lastitem = it.next() yield lastitem for item in it: if item != lastitem: yield item lastitem .= item
(Note that doing this *will* slow the code down, though, since it has to check for the existence of the name before rebinding it)
I think that most of the time it won't slow down the code as the checking will have been done during the compilation phase. It may even speed up code like this, because the compilation phase will have established that it is a rebinding and so code for testing whether a new variable is created or not is not necessarry here.
Since unbound locals are generally detected at runtime rather than compile time, I see no real reason why this case would be any different. Static checks would be in the hands the tools like pychecker (as is currently the case for references to unbound locals)
Py> def f(): ... x ... x= 3 ... Py> f() Traceback (most recent call last): File "<stdin>", line 1, in ? File "<stdin>", line 2, in f UnboundLocalError: local variable 'x' referenced before assignment
So I'd expect the compiler to generate slower code for it (probably just a LOAD/STORE pair instead of just a STORE instruction), but the optimiser should eventually be able to do something to eliminate the performance penalty due to the technically unnecessary LOAD. I doubt it will be able to beat a STORE_FAST when it comes to trying to get a performance improvement, though :)
Cheers, Nick.
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Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
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