Fredrik Lundh wrote:
> Michalis Giannakidis wrote:
>
> > Could someone please explain the reasoning/behabiour of these?
>
> in general, methods on C objects are implemented in terms of operations
> on the internal data structures, not in terms of a subset of the methods
> already provided by the object.
True, and it's also true for many Python classes. Here's a very silly
example:
class Cons(object):
def __init__(self,car,cdr):
self.car = car
self.cdr = cdr
def __getitem__(self,key):
if key == "car":
return self.car
if key == "cdr":
return self.cdr
raise KeyError(key)
def __getitem__(self,key,value):
if key == "car":
self.car = value
if key == "cdr":
self.cdr = value
raise KeyError(key)
def swap(self):
self.car,self.cdr = self.cdr,self.car
So hooking into __getitem__ and __setitem__ won't let you inpect the
swap operation. It's much the same with lists: they bypass __getitem__
and __setitem__ and go directly to their internal.
OTOH, I've written a few C types that deliberately go though slower
Python methods to allow overriding. But that has to be deliberate (for
the most part); as Frederick said, most C classes don't do that.
Carl Banks
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