Attack a sacred Python Cow

Bruno Desthuilliers bdesth.quelquechose at free.quelquepart.fr
Sat Jul 26 09:58:39 CEST 2008


Matthew Fitzgibbons a écrit :
(snip)

> As for !=, it seems like there is a technical reason for the behavior. 
> Remember, there is no default __ne__ method, so the behavior you want 
> would have to live in the interpreter. If __ne__ isn't defined, it would 
> have to try to call __eq__ and negate the result. Is there any other 
> lookup that is treated this way?

There are quite a few cases in Python where there are both a specific 
magic method  *and* a default behaviour based on another magic method if 
the specific one is not implemented. Just out of my mind:
* __contains__ and __getitem__
* __iter__ and __getitem__
* __nonzero__ and __len__

Not to mention the fact that lookup rules even check the existence of 
special methods on class attributes (remember the descriptor protocol ?)...




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