为什么这个代码会变成一个无限循环？

Question

我试图写一个代码，找到子字符串的位置，给定一个字符串。我相信在循环中有一些问题，它是一个无限循环

string="ABCDCDC"
sub_str="CDC"
i=0
while i<len(string):
    if sub_str in string:
        i=string.find(sub_str,i)
        print("Position is {}".format(i))
    else:
        break
    i+=1

我得到的实际输出：

Position is 2
Position is 4
Position is -1
Position is 2
Position is 4
Position is -1
Position is 2
Position is 4
Position is -1

预期产量：

Position is 2
Position is 4

Answer 1

你正在覆盖“i”，因此它就变成了一个无限循环。其次，您可以使用一个列表来保存索引的引用（满足您的成功标准），以避免重新打印索引以及-1

string = "ABCDCDC"
sub_str = "CDC"
i = 0
list = []
size = len(string)
while i < size:
    if sub_str in string:
        pos = string.find(sub_str, i, size)
        if pos != -1 and pos not in list:
            print("Position is {}".format(pos))
            list.append(pos)
    else:
        break
    i += 1