On Tue, Dec 27, 2016 at 10:48 AM, James Hartley <jjhart...@gmail.com> wrote: > I can successfully override __getitem__() for rvalues, but the following > example shows that more is required when used as an lvalue: > > ===8<----- > #!/usr/bin/env python > > class Foo(): > def __init__(self, n): > self.d = dict.fromkeys([i for i in range(0, n)]) > > def __getitem__(self, i): > return self.d[i] > > def main(): > foo = Foo(4) > print(foo[0]) > foo[0] = 2 # not as an lvalue? > print(foo[0]) > > if __name__ == '__main__': > main() > ===8<----- > > Python 3.4 generates the following output when this example is executed: > > None > Traceback (most recent call last): > File "./test.py", line 17, in <module> > main() > File "./test.py", line 13, in main > foo[0] = 2 > TypeError: 'Foo' object does not support item assignment > > I am surprised that the error states that the object itself cannot accept > assignment. From the C++ perspective, the underlying dictionary should be > exposed. Does Python overloading allow use of bracket overriding in > lvalues?
Hi James, You're looking for __setitem__(), see https://docs.python.org/3/reference/datamodel.html#object.__setitem__ Hope this helps, -- Zach _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
