What is an iterator and a generator, what methods should they implement, and what is the difference?

Iterator — an object that allows sequential traversal of collection elements. In Python, an iterator must implement the following methods:

• __iter__() — returns the iterator itself;
• __next__() — returns the next element or raises StopIteration if there are no more elements.

Generator — a special type of iterator created using functions with the yield keyword or generator expressions. Generators automatically implement iterator methods.

Differences:

• An iterator can be implemented manually, while a generator is easier to create using yield.
• Generators are lazy and save memory, as elements are created on demand.

Example of a generator:

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

for number in count_up_to(5):
    print(number)