Итератори и генератори

„ Програмиране с Python“, ФМИ

17.03.2011

Въпроси (1)

a, b, c, d, e, *f, g, h, i, j, k = 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
print(f[4])

Въпроси (2)

def sandwich(first_thing, *stuff):
    return stuff.count('spam')

print(sandwich('spam', 'sausage', 'spam', 'spam',
    'spam', 'sausage', 'spam', 'spam', 'spam'))

Въпроси (3)

def reversed(input):
    result = input[::-1]
    def keep_it_normal():
        result = result[::-1]
    keep_it_normal()
    return result

print(reversed('abc'))

Въпроси (4)

l = lambda x, y: x**2 + y
print(l(2, 5))

Въпроси (5)

[x for x in range(1,10) if x % 3 == 0][2]

Преговор

for x in [1,2,3]: print(x)

for x in range(42): print(x)

for x in map(lambda x: 2*x, something): print(x)

Итератор

iter и next

Пример

iterator = iter([1,2,3])
while True:
    x = next(iterator)
    print(x)

iter и next (2)

iter и next (3)

>>> m = map(lambda x: x*2, [1,2,3])
>>> iter(m) is m # True
True

m = map(lambda x: x*2, [1,2,3])
while True:
    x = next(m)
    print(x)

Въпрос

numbers = [1,2,3]
doubled = map(lambda x: x*2, l)
numbers[1] = 42
for x in doubled:
    print(x)

yield e:

Пример за yield

def musicians():
    yield 'Coltrane'
    yield 'Davis'
    yield 'Getz'

Прости числа с генератор

def primes():
    number = 2
    while True:
        if all([number % divisor for divisor in range(2, number)]):
            yield number
        number += 1

Генератори

favori

Генератори

def biscuits(pack):
    pack.open()
    while not pack.empty():
        biscuit = pack.take_out()
        yield biscuit

for biscuit in biscuits(favori):
    if biscuit.examine():
        biscuit.eat()
    else:
        biscuit.throw_away()

Generator expressions

primes = [n*n for n in range(2, 100)]
primes = (n*n for n in range(2, 100))

вградени функции

any и all

def endless():
    yield True
    while True:
        yield False

any(endless())

enumerate

enumerate (2)

names = ['Bird', 'Satchmo', 'Trane']
i = 0
for x in names:
    print(i, x)
    i += 1

enumerate (3)

names = ['Bird', 'Satchmo', 'Trane']
for i, x in enumerate(names):
    print(i, x)

zip

zip (2)

tracks = ['Take the A Train', 'Mack the Knife', 'Alabama']
names = ['The Duke', 'Satchmo', 'Trane']
for track, name in zip(tracks, names):
    print('{0} by {1}'.format(track, name))

Модулът itertools

Но първо…

Но първо…

Модули

Модули (2)

itertools

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