Python Language
필터

통사론

• 필터 (함수, 반복 가능)
• itertools.ifilter (함수, 반복 가능)
• future_builtins.filter (함수, 반복 가능)
• itertools.ifilterfalse (함수, 반복 가능)
• itertools.filterfalse (함수, 반복 가능)

매개 변수

비고

필터의 기본 사용법

하기 filter 폐기 일부 기준에 따라 시퀀스의 요소 :

names = ['Fred', 'Wilma', 'Barney']

def long_name(name):
    return len(name) > 5

filter(long_name, names)
# Out: ['Barney']

[name for name in names if len(name) > 5] # equivalent list comprehension
# Out: ['Barney']


from itertools import ifilter
ifilter(long_name, names)       # as generator (similar to python 3.x filter builtin)
# Out: <itertools.ifilter at 0x4197e10>
list(ifilter(long_name, names)) # equivalent to filter with lists
# Out: ['Barney']

(name for name in names if len(name) > 5) # equivalent generator expression
# Out: <generator object <genexpr> at 0x0000000003FD5D38>

# Besides the options for older python 2.x versions there is a future_builtin function:
from future_builtins import filter
filter(long_name, names)       # identical to itertools.ifilter
# Out: <itertools.ifilter at 0x3eb0ba8>

filter(long_name, names)        # returns a generator
# Out: <filter at 0x1fc6e443470>
list(filter(long_name, names))  # cast to list
# Out: ['Barney']

(name for name in names if len(name) > 5) # equivalent generator expression
# Out: <generator object <genexpr> at 0x000001C6F49BF4C0>

함수없이 필터링

함수 매개 변수가 None 이면 ID 함수가 사용됩니다.

list(filter(None, [1, 0, 2, [], '', 'a']))  # discards 0, [] and ''   
# Out: [1, 2, 'a']

[i for i in [1, 0, 2, [], '', 'a'] if i] # equivalent list comprehension

(i for i in [1, 0, 2, [], '', 'a'] if i) # equivalent generator expression

단락 점검 용 필터

filter (python 3.x)와 ifilter (python 2.x)는 생성기를 반환하므로 or or and 같은 단락 회로 테스트를 생성 할 때 매우 편리 할 수 ​​있습니다.

 # not recommended in real use but keeps the example short:
from itertools import ifilter as filter

 from future_builtins import filter

100보다 작은 첫 번째 요소를 찾으려면 다음과 같이하십시오.

car_shop = [('Toyota', 1000), ('rectangular tire', 80), ('Porsche', 5000)]
def find_something_smaller_than(name_value_tuple):
    print('Check {0}, {1}$'.format(*name_value_tuple)
    return name_value_tuple[1] < 100
next(filter(find_something_smaller_than, car_shop))
# Print: Check Toyota, 1000$
#        Check rectangular tire, 80$
# Out: ('rectangular tire', 80)

next 함수는 다음 요소 (이 경우 첫 번째 요소)를 제공하므로 단락 회로가되는 이유입니다.

보완 함수 : filterfalse, ifilterfalse

itertools 에는 filter 에 대한 보완 함수가 있습니다.

 # not recommended in real use but keeps the example valid for python 2.x and python 3.x
from itertools import ifilterfalse as filterfalse

from itertools import filterfalse

이것은 생성기 filter 와 정확히 똑같이 작동하지만 False 요소 만 유지합니다.

# Usage without function (None):
list(filterfalse(None, [1, 0, 2, [], '', 'a']))  # discards 1, 2, 'a' 
# Out: [0, [], '']

# Usage with function
names = ['Fred', 'Wilma', 'Barney']

def long_name(name):
    return len(name) > 5

list(filterfalse(long_name, names))
# Out: ['Fred', 'Wilma']

# Short-circuit useage with next:
car_shop = [('Toyota', 1000), ('rectangular tire', 80), ('Porsche', 5000)]
def find_something_smaller_than(name_value_tuple):
    print('Check {0}, {1}$'.format(*name_value_tuple)
    return name_value_tuple[1] < 100
next(filterfalse(find_something_smaller_than, car_shop))
# Print: Check Toyota, 1000$
# Out: ('Toyota', 1000)

# Using an equivalent generator:
car_shop = [('Toyota', 1000), ('rectangular tire', 80), ('Porsche', 5000)]
generator = (car for car in car_shop if not car[1] < 100)
next(generator)