我有以下代码(元组列表):
x = [(None, None, None), (None, None, None), (None, None, None)]
我怎么知道这基本上评估为False
?
换句话说,我怎么能这样做:
if not x: # x should evaluate to False
# do something
答案 0 :(得分:9)
使用嵌套的any()
来电:
if not any(any(inner) for inner in x):
仅当传递给它的中所有元素都是any()
时, False
才会返回False
。只有当所有元素都为假时,not any()
才是True
:
>>> x = [(None, None, None), (None, None, None), (None, None, None)]
>>> not any(any(inner) for inner in x)
True
>>> x = [(None, None, None), (None, None, None), (None, None, 1)]
>>> not any(any(inner) for inner in x)
False
答案 1 :(得分:3)
您可以将any
与itertools.chain
一起使用,它比嵌套any
更快,因为不需要python for-loop:
很少有其他选择:
not any (chain.from_iterable(x))
not any (chain(*x))
not any(map(any,x))
not any(imap(any,x)) #itertools.imap
>>> from itertools import chain,imap
>>> x = [(None, None, None), (None, None, None), (None, None, None)]
>>> %timeit not any (chain.from_iterable(x)) #winner
100000 loops, best of 3: 1.08 us per loop
>>> %timeit not any (chain(*x))
1000000 loops, best of 3: 1.29 us per loop
>>> %timeit not any(any(inner) for inner in x)
100000 loops, best of 3: 1.76 us per loop
>>> %timeit not any(map(any,x))
100000 loops, best of 3: 1.5 us per loop
>>> %timeit not any(imap(any,x))
100000 loops, best of 3: 1.37 us per loop
>>> x = [(None, None, None), (None, None, None), (None, None, None)]*1000
>>> %timeit not any (chain.from_iterable(x)) #winner
1000 loops, best of 3: 462 us per loop
>>> %timeit not any (chain(*x))
1000 loops, best of 3: 537 us per loop
>>> %timeit not any(any(inner) for inner in x)
1000 loops, best of 3: 1.26 ms per loop
>>> %timeit not any(map(any,x))
1000 loops, best of 3: 672 us per loop
>>> %timeit not any(imap(any,x))
1000 loops, best of 3: 765 us per loop
>>> x = [(None, None, None), (None, None, None), (None, None, None)]*10**5
>>> %timeit not any (chain.from_iterable(x)) #winner
10 loops, best of 3: 50.1 ms per loop
>>> %timeit not any (chain(*x))
10 loops, best of 3: 70.3 ms per loop
>>> %timeit not any(any(inner) for inner in x)
10 loops, best of 3: 127 ms per loop
>>> %timeit not any(map(any,x))
10 loops, best of 3: 76.2 ms per loop
>>> %timeit not any(imap(any,x))
1 loops, best of 3: 64.9 ms per loop