Iterator (iter()) function in Python.

For dictionary, I can use iter() for iterating over keys of the dictionary.

y = {"x":10, "y":20}
for val in iter(y):
    print val

When I have the iterator as follows,

class Counter:
    def __init__(self, low, high):
        self.current = low
        self.high = high

    def __iter__(self):
        return self

    def next(self):
        if self.current > self.high:
            raise StopIteration
        else:
            self.current += 1
            return self.current - 1

Why can't I use it this way

x = Counter(3,8)
for i in x:
    print x

nor

x = Counter(3,8)
for i in iter(x):
    print x

but this way?

for c in Counter(3, 8):
    print c

What's the usage of iter() function?

ADDED

I guess this can be one of the ways of how iter() is used.

class Counter:
    def __init__(self, low, high):
        self.current = low
        self.high = high

    def __iter__(self):
        return self

    def next(self):
        if self.current > self.high:
            raise StopIteration
        else:
            self.current += 1
            return self.current - 1

class Hello:
    def __iter__(self):
        return Counter(10,20)

x = iter(Hello())
for i in x:
    print i