Про итераторы кратко

Самая важная схема занятия:

itertools

list(map(len, ['4', 'fdd']))

[1, 3]

1 in [1, 2, 3]

True

1 in {1, 2, 3}      # sets

True

1 in (1, 2, 3)      # tuples

True

d = {1: 'foo', 2: 'bar', 3: 'qux'}

1 in d

True

s = 'foobar'

'b' in s

True

for item in [1, 3, 4]:
  print(item)

1
3
4

lst = [1, 2, 3]
x = iter(lst)
print(type(x))
print(x)

<class 'list_iterator'>
<list_iterator object at 0x000001C1262DAC50>

next(x)

1

next(x)

2

next(x)

3

next(x)

---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Cell In[28], line 1
----> 1 next(x)

StopIteration: 

from itertools import count
counter = count(start=13)

next(counter)

13

def repeater(value):
    while True:
        yield value

generator_obj = repeater('Эй')
next(generator_obj)

'Эй'

next(generator_obj)

'Эй'

numbers = [1, 2, 3, 4, 5, 6]
[x * x for x in numbers]

[1, 4, 9, 16, 25, 36]

lazy_squares = (x * x for x in numbers)

lazy_squares

<generator object <genexpr> at 0x7f671ce74cd0>

next(lazy_squares)

1

gen = (x * x for x in range(2328346283764826348726347628374628376482763482763482634876))
print(next(gen))
print(next(gen))
print(next(gen))
# отложенные вычисления, т.е. один элемент по запросу

0
1
4