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问题描述
我有这样的示例列表:
example_list = [['aaa'], ['fff', 'gg'], ['ff'], ['', 'gg']]
现在,我检查它是否具有空字符串,如下所示:
Now, I check if it has empty string like this:
has_empty = False;
for list1 in example_list:
for val1 in list1:
if val1 == '':
has_empty = True
print(has_empty)
这可以正常工作,因为它可以打印True,但是否正在寻找更多的pythonik方法?
This works OK as it prints True, but looking for more pythonik method?
推荐答案
您可以使用 itertools.chain.from_iterable
:
You can use itertools.chain.from_iterable
:
>>> from itertools import chain
>>> example_list = [['aaa'], ['fff', 'gg'], ['ff'], ['', 'gg']]
>>> '' in chain.from_iterable(example_list)
True
仅在内部列表更大(超过100个项目)的情况下,将any
与生成器一起使用会比上面的示例更快,因为那样,使用Python for循环的速度代价将由快速补偿. in
-操作:
Just in case if the inner lists are bigger(more than 100 items) then using any
with a generator will be faster than the above example because then the speed penalty of using a Python for-loop is compensated by the fast in
-operation:
>>> any('' in x for x in example_list)
True
时间比较:
>>> example_list = [['aaa']*1000, ['fff', 'gg']*1000, ['gg']*1000]*10000 + [['']*1000]
>>> %timeit '' in chain.from_iterable(example_list)
1 loops, best of 3: 706 ms per loop
>>> %timeit any('' in x for x in example_list)
1 loops, best of 3: 417 ms per loop
# With smaller inner lists for-loop makes `any()` version little slow
>>> example_list = [['aaa'], ['fff', 'gg'], ['gg', 'kk']]*10000 + [['']]
>>> %timeit '' in chain.from_iterable(example_list)
100 loops, best of 3: 2 ms per loop
>>> %timeit any('' in x for x in example_list)
100 loops, best of 3: 2.65 ms per loop
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