字符串反转的几种方法

def reverse_str(s):
    from functools import reduce
    res = s[::-1]   # 切片    
    res = "".join(list(reversed(s)))    # 反转函数
    res = reduce(lambda x,y:y+x, s)     # reduce
    print(res)

def recursion_reverse_str(s):
    # 递归
    if len(s) < 1:
        return ""
    return recursion_reverse_str(s[1:]) + s[0]

def stack_reverse_str(s):
    # 栈
    li = list(s)
    res = ""
    while len(li)>0:
        res += li.pop()
    return res

def loop_str(s):
    # 循环
    res = ""
    for i in range(len(s)-1, -1, -1):
        res += s[i]
    return res