Iterators and Generators

What You’ll Learn

You’ll learn advanced iteration techniques that save memory when working with large sequences.

Iterators

An iterator is an object that contains a countable number of values and can be iterated upon. Lists, tuples, dictionaries, and sets are all iterable objects. They are iterable containers which you can get an iterator from.

mytuple = ("apple", "banana", "cherry")
myit = iter(mytuple)

print(next(myit)) # apple
print(next(myit)) # banana

Generators

Generators are a simple way of creating iterators. Instead of using return in a function, you use yield.

When a function uses yield, it doesn’t execute and return a single value. Instead, it returns a generator object that yields one value at a time on demand. This uses very little memory!

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

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

You can loop over generators just like lists:

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