As we mentioned earlier, a for loop only needs an iterable object. Lists, in particular, are iterable objects. This means that a list is able to create an iterator from its contents. In fact, this is true for any object (not only lists): any object may be made iterable.
This is achieved via the method __iter__, which should return an iterator. Here we give an example where the method __iter__ is a generator:
class OdeStore: """ Class to store results of ode computations """ def __init__(self, data): "data is a list of the form [[t0, u0], [t1, u1],...]" self.data = data def __iter__(self): "By default, we iterate on the values u0, u1,..." for t, u in self.data: yield u store = OdeStore([[0, 1], [0.1, 1.1], [0.2, 1.3]]) for u in store: print(u) # result: 1, 1.1, 1.3 list(store) # [1, 1.1, 1...