Possible Duplicate:
Why does defining getitem on a class make it iterable in python?
class b: def __getitem__(self, k): return k cb = b() for k in cb: print k I get the output:
0 1 2 3 4 5 6 7 8 ..... Iterating over instance of class b, emits integers. Why is that?
(came across the above program when looking at Why does defining __getitem__ on a class make it iterable in python?)
Because the for-loop is implemented for objects that define __getitem__ but not __iter__ by passing successive indices to the object's __getitem__ method. See the effbot. (What really happens under the covers IIUC is a bit more complicated: if the object doesn't provide __iter__, then iter is called on the object, and the iterator that iter returns does the calling of the underlying object's __getitem__.)
