Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote:
> Simply not to introduce special cases I guess. If you write ``x.a +=
> b`` then `x.a` will be rebound whether an `a.__iadd__()` exists or
> not. Otherwise one would get interesting subtle differences with
> properties for example. If `x.a` is a property that checks if the
> value satisfies some constraints ``x.a += b`` would trigger the set
> method only if there is no `__iadd__()` involved if there's no
> rebinding.
Unfortunately that doesn't work very well. If the validation rejects the
new value the original is still modified:
>>> class C(object):
def setx(self, value):
if len(value)>2:
raise ValueError
self._x = value
def getx(self):
return self._x
x = property(getx, setx)
>>> o = C()
>>> o.x = []
>>> o.x += ['a']
>>> o.x += ['b']
>>> o.x += ['c']
Traceback (most recent call last):
File "<pyshell#27>", line 1, in <module>
o.x += ['c']
File "<pyshell#22>", line 4, in setx
raise ValueError
ValueError
>>> o.x
['a', 'b', 'c']
>>>
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