Chapter 8: Map, Filter, & Reduce

Iterators vs. Iterables

numbers = [7, 11, 8, 5, 3, 12, 2, 6, 9, 10, 1, 4]

iterator1 = iter(numbers)

iterator2 = iter(numbers)

type(iterator1)

list_iterator

next(iterator1), next(iterator1), next(iterator1)

(7, 11, 8)

next(iterator1), next(iterator2)

(5, 7)

zipper = zip(iterator1, iterator2)

zipper

<zip at 0x7f2788118b00>

type(zipper)

zip

for x, y in zipper:
    print(x, "and", y, end="   ")

7 and 4   8 and 5   9 and 6   10 and 7   11 and 8   12 and 9   

next(iterator1)

---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
Cell In[25], line 1
----> 1 next(iterator1)

StopIteration: 

next(iterator2)

10

The for Statement (revisited)

iterable = [0, 1, 2, 3, 4]

for element in iterable:
    print(element, end=" ")

0 1 2 3 4 

iterator = iter(iterable)

while True:
    try:
        element = next(iterator)
    except StopIteration:
        break
    else:
        print(element, end=" ")

del iterator

0 1 2 3 4 

sorted() vs. reversed()

numbers = [7, 11, 8, 5, 3, 12, 2, 6, 9, 10, 1, 4]

memoryless = range(1, 13)

sorted(numbers)

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

sorted(memoryless)

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

reversed(numbers)

<list_reverseiterator at 0x7f2788158880>

reversed(memoryless)

<range_iterator at 0x7f2788158fc0>

list(reversed(numbers))

[4, 1, 10, 9, 6, 2, 12, 3, 5, 8, 11, 7]

tuple(reversed(memoryless))

(12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

for number in reversed(numbers):
    print(number, end=" ")

4 1 10 9 6 2 12 3 5 8 11 7 

for element in reversed(memoryless):
    print(element, end=" ")

12 11 10 9 8 7 6 5 4 3 2 1 

numbers

[7, 11, 8, 5, 3, 12, 2, 6, 9, 10, 1, 4]

memoryless

range(1, 13)