Question

def subStringMatchExact(word,subword):
    if len(word)<len(subword):
        print 'substring is bigget than the string, please type another substring.'
        return None    
    else:
        for i in xrange(0,len(word)):
            t = ()
            j = 0
            while word[i] == subword[j]:
                j = j+1 
                i = i+1
                if j == len(subword):
                    t = t+(i-j,)
                    return t



print subStringMatchExact('afgbcdefg', 'fg')

如何让循环重新开始并跟踪i的值？

Answer 1

您没有指定要再次运行哪个循环，但是在结束后执行该循环的唯一方法是将其放在另一个循环中。您可以通过将其存储在for循环范围之外的另一个变量中来跟踪i。像这样：

def subStringMatchExact(word,subword):
    if len(word)<len(subword):
        print 'substring is bigger than the string, please type another substring.'
        return None
    else:
        lasti=0 # <- lasti is outside the scope of the for loop 
                # So it will save the value even after the for loop terminates
        for i in xrange(0,len(word)):
            t = []
            j = 0
            lasti=i # assigning i to lasti 
            while word[i] == subword[j]:
                j = j+1
                i = i+1
                if j == len(subword):
                    t = t+(i-j,)
                    return t

如果您试图获取子字的起始位置和结束位置，则可以执行此操作：

def subStringMatchExact(word,subword):
    if len(word)<len(subword):
        print 'substring is bigger than the string, please type another substring.'
        return None
    else:
        start, end = -1, -1
        for i in range(0,len(word)):
            for  j in range(0,len(subword)):
                if word[i] == subword[j]:
                    if start == -1:
                        start = i
                    end = (j+i-1)
        return [start,end]

Answer 2

如果您正在尝试即兴创建代码以从字符串匹配错误的地方继续，那么For循环就不是了。这将有所帮助：

def subStringMatchExact(word,subword):
    if len(word)<len(subword):
        print 'substring is bigget than the string, please type another substring.'
        return None    
    else:
        i = 0
        while i < len(word):
            t = ()
            j = 0
            while word[i] == subword[j]:
                j = j+1 
                i = i+1
                if j == len(subword):
                    t = t+(i,)
                    return t

你不能在for循环方面跳跃或跳跃。你需要使用while循环。请注意，除了教育目的之外，不要走这条路。这可以使用字符串索引方法轻松完成：

def subStringMatchExact(word,subword):
    if len(word) < len(subword):
        print 'substring is bigger than the string, please type another substring.'
    if subword in word:
        word_index = word.index(subword)
        return tuple(range(word_index, word_index+len(subword)))

while循环使用if语句

2 个答案: