Carl M. Johnson wrote:
On Tue, May 31, 2011 at 7:48 PM, Georg Brandl wrote:
Because x += y is equivalent to
x = x.__iadd__(y)
and therefore an assignment is going on here. Therefore, it's only logical to treat it as such when determining scopes.
But the difference is that you can only use += if the LHS name already exists and is defined. So, it couldn't possibly be referring to a local name if it's the only assignment-like statement within a function body. How could it refer to a local if it has to refer to something that already exists?
Two problems. Firstly, what error should be raised here? --> def accum(): ... x = 0 ... def inner(): ... x1 += 1 ... return x ... return inner Secondly, the += operator may or may not be a mutating operator depending on the object it's used on: if the object does not have a __iadd__ method, it's not mutating; even if it does have an __iadd__ method, it may not be mutating -- it's up to the object to decide. --> class ex_int(int): ... def __iadd__(self, other): ... return self + other ... --> x = ex_int(7) --> x.__iadd__(3) 10 --> x 7 --> x = [1, 2, 3] --> x.__iadd__([4]) [1, 2, 3, 4] --> x [1, 2, 3, 4] -1 on changing the semantics. ~Ethan~