Return a non iterator from __iter__

Question

class test(object):
    def __init__(self):
        pass
    def __iter__(self):
        return \"my string\"

o = test()
print iter(o)

Why does th

Answer 1

The purpose of __iter__ magic function is to return something that you can iterate (e.g. loop) through. The most common solution is to return iter(something) where something could be a list, a tuple, set, dictionary, a string... anything that we can iterate through. Take a look at this example:

class Band:
    def __init__(self):
        self.members = []

    def add_member(self, name):
        self.members.append(name)

    def __iter__(self):
        return iter(self.members)

if __name__ == '__main__':
    band = Band()
    band.add_member('Peter')
    band.add_member('Paul')
    band.add_member('Mary')

    # Magic of __iter__:
    for member in band:
        print(member)

Output:

Peter
Paul
Mary

In this case, the __iter__ magic function allows us to loop through band as if it is a collection of members. That means in your case, return "my string" will not do. If you want a list of chars in "my string":

def __iter__(self):
    return iter("my string")  # ==> m, y, ' ', s, t, r, i, n, g

However, if you want to return a list with a single element "my string", then:

def __iter__(self):
    return iter(["my string"])