itertools — 用于迭代的函数

合并和拆分迭代器

# itertools_chain.py
from itertools import *

for i in chain([1, 2, 3], ['a', 'b', 'c']):
    print(i, end=' ')
print()

# itertools_chain_from_iterable.py
from itertools import *


def make_iterables_to_chain():
    yield [1, 2, 3]
    yield ['a', 'b', 'c']


for i in chain.from_iterable(make_iterables_to_chain()):
    print(i, end=' ')
print()

# itertools_zip.py
for i in zip([1, 2, 3], ['a', 'b', 'c']):
    print(i)

# itertools_zip_longest.py
from itertools import *

r1 = range(3)
r2 = range(2)

print('zip stops early:')
print(list(zip(r1, r2)))

r1 = range(3)
r2 = range(2)

print('\nzip_longest processes all of the values:')
print(list(zip_longest(r1, r2)))

# itertools_islice.py
from itertools import *

print('Stop at 5:')
for i in islice(range(100), 5):
    print(i, end=' ')
print('\n')

print('Start at 5, Stop at 10:')
for i in islice(range(100), 5, 10):
    print(i, end=' ')
print('\n')

print('By tens to 100:')
for i in islice(range(100), 0, 100, 10):
    print(i, end=' ')
print('\n')

# itertools_tee.py
from itertools import *

r = islice(count(), 5)
i1, i2 = tee(r)

print('i1:', list(i1))
print('i2:', list(i2))

# itertools_tee_error.py
from itertools import *

r = islice(count(), 5)
i1, i2 = tee(r)

print('r:', end=' ')
for i in r:
    print(i, end=' ')
    if i > 1:
        break
print()

print('i1:', list(i1))
print('i2:', list(i2))

转换输入

# itertools_map.py

def times_two(x):
    return 2 * x


def multiply(x, y):
    return (x, y, x * y)


print('Doubles:')
for i in map(times_two, range(5)):
    print(i)

print('\nMultiples:')
r1 = range(5)
r2 = range(5, 10)
for i in map(multiply, r1, r2):
    print('{:d} * {:d} = {:d}'.format(*i))

print('\nStopping:')
r1 = range(5)
r2 = range(2)
for i in map(multiply, r1, r2):
    print(i)

# itertools_starmap.py
from itertools import *

values = [(0, 5), (1, 6), (2, 7), (3, 8), (4, 9)]

for i in starmap(lambda x, y: (x, y, x * y), values):
    print('{} * {} = {}'.format(*i))

生产新值

# itertools_count.py
from itertools import *

for i in zip(count(1), ['a', 'b', 'c']):
    print(i)

# itertools_count_step.py
import fractions
from itertools import *

start = fractions.Fraction(1, 3)
step = fractions.Fraction(1, 3)

for i in zip(count(start, step), ['a', 'b', 'c']):
    print('{}: {}'.format(*i))

# itertools_cycle.py
from itertools import *

for i in zip(range(7), cycle(['a', 'b', 'c'])):
    print(i)

# itertools_repeat.py
from itertools import *

for i in repeat('over-and-over', 5):
    print(i)

# itertools_repeat_zip.py
from itertools import *

for i, s in zip(count(), repeat('over-and-over', 5)):
    print(i, s)

# itertools_repeat_map.py
from itertools import *

for i in map(lambda x, y: (x, y, x * y), repeat(2), range(5)):
    print('{:d} * {:d} = {:d}'.format(*i))

过滤

# itertools_dropwhile.py
from itertools import *


def should_drop(x):
    print('Testing:', x)
    return x < 1


for i in dropwhile(should_drop, [-1, 0, 1, 2, -2]):
    print('Yielding:', i)

# itertools_takewhile.py
from itertools import *


def should_take(x):
    print('Testing:', x)
    return x < 2


for i in takewhile(should_take, [-1, 0, 1, 2, -2]):
    print('Yielding:', i)

# itertools_filter.py
from itertools import *


def check_item(x):
    print('Testing:', x)
    return x < 1


for i in filter(check_item, [-1, 0, 1, 2, -2]):
    print('Yielding:', i)

# itertools_filterfalse.py
from itertools import *


def check_item(x):
    print('Testing:', x)
    return x < 1


for i in filterfalse(check_item, [-1, 0, 1, 2, -2]):
    print('Yielding:', i)

# itertools_compress.py
from itertools import *

every_third = cycle([False, False, True])
data = range(1, 10)

for i in compress(data, every_third):
    print(i, end=' ')
print()

数据分组

# itertools_groupby_seq.py
import functools
from itertools import *
import operator
import pprint


@functools.total_ordering
class Point:

    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return '({}, {})'.format(self.x, self.y)

    def __eq__(self, other):
        return (self.x, self.y) == (other.x, other.y)

    def __gt__(self, other):
        return (self.x, self.y) > (other.x, other.y)


# Create a dataset of Point instances
data = list(map(Point,
                cycle(islice(count(), 3)),
                islice(count(), 7)))
print('Data:')
pprint.pprint(data, width=35)
print()

# Try to group the unsorted data based on X values
print('Grouped, unsorted:')
for k, g in groupby(data, operator.attrgetter('x')):
    print(k, list(g))
print()

# Sort the data
data.sort()
print('Sorted:')
pprint.pprint(data, width=35)
print()

# Group the sorted data based on X values
print('Grouped, sorted:')
for k, g in groupby(data, operator.attrgetter('x')):
    print(k, list(g))
print()

合并输入

# itertools_accumulate.py
from itertools import *

print(list(accumulate(range(5))))
print(list(accumulate('abcde')))

# itertools_accumulate_custom.py
from itertools import *


def f(a, b):
    print(a, b)
    return b + a + b


print(list(accumulate('abcde', f)))

# itertools_product.py
from itertools import *
import pprint

FACE_CARDS = ('J', 'Q', 'K', 'A')
SUITS = ('H', 'D', 'C', 'S')

DECK = list(
    product(
        chain(range(2, 11), FACE_CARDS),
        SUITS,
    )
)

for card in DECK:
    print('{:>2}{}'.format(*card), end=' ')
    if card[1] == SUITS[-1]:
        print()

# itertools_product_ordering.py
from itertools import *
import pprint

FACE_CARDS = ('J', 'Q', 'K', 'A')
SUITS = ('H', 'D', 'C', 'S')

DECK = list(
    product(
        SUITS,
        chain(range(2, 11), FACE_CARDS),
    )
)

for card in DECK:
    print('{:>2}{}'.format(card[1], card[0]), end=' ')
    if card[1] == FACE_CARDS[-1]:
        print()

# itertools_product_repeat.py
from itertools import *


def show(iterable):
    for i, item in enumerate(iterable, 1):
        print(item, end=' ')
        if (i % 3) == 0:
            print()
    print()


print('Repeat 2:\n')
show(list(product(range(3), repeat=2)))

print('Repeat 3:\n')
show(list(product(range(3), repeat=3)))

# itertools_permutations.py
from itertools import *


def show(iterable):
    first = None
    for i, item in enumerate(iterable, 1):
        if first != item[0]:
            if first is not None:
                print()
            first = item[0]
        print(''.join(item), end=' ')
    print()


print('All permutations:\n')
show(permutations('abcd'))

print('\nPairs:\n')
show(permutations('abcd', r=2))

# itertools_combinations.py
from itertools import *


def show(iterable):
    first = None
    for i, item in enumerate(iterable, 1):
        if first != item[0]:
            if first is not None:
                print()
            first = item[0]
        print(''.join(item), end=' ')
    print()


print('Unique pairs:\n')
show(combinations('abcd', r=2))

# itertools_combinations_with_replacement.py
from itertools import *


def show(iterable):
    first = None
    for i, item in enumerate(iterable, 1):
        if first != item[0]:
            if first is not None:
                print()
            first = item[0]
        print(''.join(item), end=' ')
    print()


print('Unique pairs:\n')
show(combinations_with_replacement('abcd', r=2))