Can an iterator object act as a generator, and vice versa?

In Python, iterator and generator objects are related but not always interchangeable.

• An iterator is an object that implements the __iter__() method (which returns itself) and the __next__() method (which returns the next element or raises StopIteration). Iterators can be created manually or returned by functions.

• A generator is a special type of iterator created using a function with the yield keyword or a generator expression. Generators automatically implement the iterator methods.

Thus, every generator is an iterator, but not every iterator is a generator. Generators are convenient because they allow writing lazy sequences without explicitly creating an iterator class.

Example of a generator:

def count_up_to(n):
    i = 1
    while i <= n:
        yield i
        i += 1

gen = count_up_to(3)
print(next(gen))  # 1
print(next(gen))  # 2
print(next(gen))  # 3

If an object implements the iterator methods, it can act as a generator in the iterator sense, but it does not have all the features of generator functions (such as maintaining state via yield).