Question

检查字符串是否包含列表中任何项目的某些字符的最快方法是什么？

目前，我正在使用这种方法：

lestring = "Text123"

lelist = ["Text", "foo", "bar"]

for x in lelist:
    if lestring.count(x):
        print 'Yep. "%s" contains characters from "%s" item.' % (lestring, x)

如果没有迭代，有没有办法做到这一点（我认为这会让它更快。）？

Answer 1

您可以尝试使用成员资格检查列表理解

>>> lestring = "Text123"
>>> lelist = ["Text", "foo", "bar"]
>>> [e for e in lelist if e in lestring]
['Text']

与您的实现相比，虽然LC有一个隐式循环，但它更快，因为没有显式函数调用，如count

的情况

与Joe的实现相比，你的实现速度更快，因为过滤器函数需要在循环中调用两个函数lambda和count

>>> def joe(lelist, lestring):
    return ''.join(random.sample(x + 'b'*len(x), len(x)))

>>> def uz(lelist, lestring):
    for x in lelist:
        if lestring.count(x):
            return 'Yep. "%s" contains characters from "%s" item.' % (lestring, x)


>>> def ab(lelist, lestring):
    return [e for e in lelist if e in lestring]

>>> t_ab = timeit.Timer("ab(lelist, lestring)", setup="from __main__ import lelist, lestring, ab")
>>> t_uz = timeit.Timer("uz(lelist, lestring)", setup="from __main__ import lelist, lestring, uz")
>>> t_joe = timeit.Timer("joe(lelist, lestring)", setup="from __main__ import lelist, lestring, joe")
>>> t_ab.timeit(100000)
0.09391469893125759
>>> t_uz.timeit(100000)
0.1528471407273173
>>> t_joe.timeit(100000)
1.4272649857800843

Jamie评论的解决方案对于较短的字符串来说速度较慢。这是测试结果

>>> def jamie(lelist, lestring):
    return next(itertools.chain((e for e in lelist if e in lestring), (None,))) is not None

>>> t_jamie = timeit.Timer("jamie(lelist, lestring)", setup="from __main__ import lelist, lestring, jamie")
>>> t_jamie.timeit(100000)
0.22237164127909637

如果您需要布尔值，对于较短的字符串，只需修改上面的LC表达式

[e in lestring for e in lelist if e in lestring]

或者对于更长的字符串，您可以执行以下操作

>>> next(e in lestring for e in lelist if e in lestring)
True

或

>>> any(e in lestring for e in lelist)

Answer 2

filter(lambda x: lestring.count(x), lelist)

这将返回您尝试查找的所有字符串作为列表。

Answer 3

如果要测试是否有共同的字符（不是单词或段），请在列表中创建一个字母集，然后再次检查字符串中的字母：

char_list = set(''.join(list_of_words))
test_set = set(string_to_teat)
common_chars = char_list.intersection(test_set)

但是我假设你只想找一个共同的角色......

Answer 4

esmre 库可以解决问题。在您的情况下，更简单的 esm （esmre的一部分）就是您想要的。

https://pypi.python.org/pypi/esmre/

https://code.google.com/p/esmre/

他们有很好的文档和示例：取自他们的例子：

>>> import esm
>>> index = esm.Index()
>>> index.enter("he")
>>> index.enter("she")
>>> index.enter("his")
>>> index.enter("hers")
>>> index.fix()
>>> index.query("this here is history")
[((1, 4), 'his'), ((5, 7), 'he'), ((13, 16), 'his')]
>>> index.query("Those are his sheep!")
[((10, 13), 'his'), ((14, 17), 'she'), ((15, 17), 'he')]
>>>

我进行了一些性能测试：

import random, timeit, string, esm

def uz(lelist, lestring):
    for x in lelist:
        if lestring.count(x):
            return 'Yep. "%s" contains characters from "%s" item.' % (lestring, x)



def ab(lelist, lestring):
    return [e for e in lelist if e in lestring]


def use_esm(index, lestring):
    return index.query(lestring)

for TEXT_LEN in [5, 50, 1000]:
    for SEARCH_LEN in [5, 20]:
        for N in [5, 50, 1000, 10000]:
            if TEXT_LEN < SEARCH_LEN:
                continue

            print 'TEXT_LEN:', TEXT_LEN, 'SEARCH_LEN:', SEARCH_LEN, 'N:', N

            lestring = ''.join((random.choice(string.ascii_uppercase + string.digits) for _ in range(TEXT_LEN)))
            lelist = [''.join((random.choice(string.ascii_uppercase + string.digits) for _ in range(SEARCH_LEN))) for _
                      in range(N)]

            index = esm.Index()
            for i in lelist:
                index.enter(i)
            index.fix()

            t_ab = timeit.Timer("ab(lelist, lestring)", setup="from __main__ import lelist, lestring, ab")
            t_uz = timeit.Timer("uz(lelist, lestring)", setup="from __main__ import lelist, lestring, uz")
            t_esm = timeit.Timer("use_esm(index, lestring)", setup="from __main__ import index, lestring, use_esm")

            ab_time = t_ab.timeit(1000)
            uz_time = t_uz.timeit(1000)
            esm_time = t_esm.timeit(1000)

            min_time = min(ab_time, uz_time, esm_time)
            print '  ab%s: %f' % ('*' if ab_time == min_time else '', ab_time)
            print '  uz%s: %f' % ('*' if uz_time == min_time else '', uz_time)
            print '  esm%s %f:' % ('*' if esm_time == min_time else '', esm_time)

并且结果主要取决于一个人正在寻找的项目数量（在我的情况下，＆＃39; N＆＃39;）：

TEXT_LEN: 1000 SEARCH_LEN: 20 N: 5
  ab*: 0.001733
  uz: 0.002512
  esm 0.126853:

TEXT_LEN: 1000 SEARCH_LEN: 20 N: 50
  ab*: 0.017564
  uz: 0.023701
  esm 0.079925:

TEXT_LEN: 1000 SEARCH_LEN: 20 N: 1000
  ab: 0.370371
  uz: 0.489523
  esm* 0.133783:

TEXT_LEN: 1000 SEARCH_LEN: 20 N: 10000
  ab: 3.678790
  uz: 4.883575
  esm* 0.259605:

Python - 检查字符串是否包含列表中任何项目中的特定字符的最快方法

4 个答案: