6. Iterators¶

Lazy evaluation,
Memory efficient,
Used in many places
- open,
- zip,
- enumerate,
- reversed

from typing import Iterable
print(issubclass(range, Iterable))

True

Hint

You can check different types in same way ex. lists, strings

from typing import Iterable, Iterator

print(isinstance(range(10), Iterable))
print(hasattr(range(10),'__iter__'))
print(callable(range(10).__iter__))
print(isinstance(iter([1,2]) , Iterator))

True
True
True
True

6.1. Iterators vs lists¶

# Not using too much memory - iterating on the fly
for i in ( i ** 2 for i in range(10**8)):
    print(i)

# using a lot of memory

lista = [ i ** 2 for i in range(10**8)]

Hint

Compare proces for list and generator using ps aux PID Additionally you may use linux function watch -d -n 0.1

6.2. Defining iterators¶

class Numbers:
    def __iter__(self):
        self.value = 1
        return self

    def __next__(self):
        value = self.value
        self.value += 1
        return value

numbers = Numbers()
my_iter = iter(numbers)

print(next(my_iter))
print(next(my_iter))
print(next(my_iter))

1
2
3

6.3. Zip¶

from typing import Iterable, Iterator

za = zip([1,2,3], ['a', 'b', 'c'])
print(isinstance(za, Iterable))
print(isinstance(za, Iterator))

True
True

6.4. Exercises¶

We got list of expenses in specific days of the week

expenses = [11.25, 18.0, 20.0, 10.75, 9.50]

Print all numbers (without using range / len) google

if form like: “parking cost 1: 11.25”

Hint

You may use enumberate