Python字符串中查找子串小技巧

WBOY
Release: 2016-06-06 11:24:58
Original
1400 people have browsed it

惭愧啊,今天写了个查找子串的Python程序被BS了…

如果让你写一个程序检查字符串s2中是不是包含有s1。也许你会很直观的写下下面的代码:

代码如下:


#determine whether s1 is a substring of s2
def isSubstring1(s1,s2):
    tag = False
    len1 = len(s1)
    len2 = len(s2)
    for i in range(0,len2):
        if s2[i] == s1[0]:
            for j in range(0,len1):
                if s2[i]==s1[j]:
                    tag = True
    return tag

可是这是Python,我们可以利用字符串自带的find()方法,于是可以这样:

代码如下:


def isSubstring2(s1,s2):
    tag = False
    if s2.find(s1) != -1:
        tag = True
    return tag


悲情的事就在于此,原来Python中的关键字"in”不仅可以用于列表、元祖等数据类型,还可以用于字符串。所以,这里只需要直接一行代码搞定:

代码如下:


def isSubstring3(s1,s2):
    return s1 in s2


后知后觉了,惭愧;-)

类似的,假设要在字符串中,查找多个子串是否存在,并打印出这些串和首次出现的位置:

代码如下:


def findSubstrings(substrings,destString):
    res =  map(lambda x:str([destString.index(x),x]),filter(lambda x:x in destString,substrings))
    if res:
        return ', '.join(list(res))
 
;-)  very cool~


UPDATE: 如果你不习惯最后面这种看起来很复杂的语法也没关系,可以使用列表解析,更加简洁:

代码如下:


def findSubstrings(substrings,destString):
    return ', '.join([str([destString.index(x),x]) for x in substrings if x in destString])

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