Python: filter(None, [list of bools]) 行为

Question

编辑:阅读建议的链接后，我不知道为什么它被标记为重复。告我。

谁能帮我理解为什么 filter(None, [list of bools]) 会删除 False 值？

采取以下措施:

low = 25 
high = 35
to_match = [15, 30, 32, 99]
def check(low, high, to_match):
    return [low <= i <= high for i in to_match]

check(low, high, to_match) 返回 [False, True, True, False]

filter(None, check(low, high, to_match)) 返回 [True, True]

所以我想，Python 一定认为 False 是 None!但令我惊讶的是，False is None 返回 False!

A) 我错过了什么？

B) 如何从 [True, None, False] 中仅过滤 None 值？

Answer 1

如果要过滤掉 None，请使用:

filter(lambda x: x is not None, [list of bools])

或

[x for x in [list of bools] if x is not None]

filter takes a function, not a value . filter(None, ...) 是 filter(lambda x: x, ...) 的简写——它将过滤掉 false-y 的值(强调我的):

filter(function, iterable)

Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for item in iterable if item] if function is None.