python-字符串替换

第一种方法：直接调用replace()

def strreplace(str, oldstr, newstr):

     return str.replace(oldstr,newstr)

第二种方法：利用re模块正则

 def strreplace(str, oldstr, newstr):

     #先编译正则

     m=re.compile(oldstr)

#     #替换字符串中的匹配项

     ret=m.sub(newstr,str)

     return ret

第三种方法：实现替换函数

# 找到替换字符的开始位置

def getindex(str, key):

    n1 = len(str)

    n2 = len(key)

    i = 0

    j = 0

    while i < n1:

        if str[i] != key[j]:

            i = i + 1

        else:

            # index为开始位置

            index = i

            while j < n2:

                if str[i] == key[j]:

                    i += 1

                    j += 1

                else:

                    #如果不相等继续找，替换字符串的下标重新开始，置为0

                    j = 0

                    break

            return index

    return -1

def strreplace(str, oldstr, newstr):

    index = getindex(str, oldstr)

    # print(index)

    step = index + len(oldstr)

    return str[:index] + newstr + str[step:]

str = strreplace('hello world china', 'world', 'hi')

结果：hello hi china