Am 13.01.2012 13:30 schrieb Chris Angelico:
It seems there's a distinct difference between a+=b (in-place
addition/concatenation) and a=a+b (always rebinding),
There is indeed.
a = a + b is a = a.__add__(b), while
a += b is a = a.__iadd__(b).
__add__() is supposed to leave the original object intact and return a
new one, while __iadd__() is free to modify (preference, to be done if
possible) or return a new one.
A immutable object can only return a new one, and its __iadd__()
behaviour is the same as __add__().
A mutable object, however, is free to and supposed to modify itself and
then return self.
Thomas
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