我自己想的办法，不知道除了测试项之外会不会报错，感觉有点麻烦~~o(╥﹏╥)o

def trim(s):
    if s=='':
        return s
    else:
        start=0
        end=0
        for i in range(len(s)):
            if s[i:i+1]==' ':
                start=start+1
            else:
                break
        s=s[start:]
        for j in range(len(s)):
            if s[len(s)-j-1:len(s)-j]==' ':
                end=end+1
            else:
                break
        s=s[0:len(s)-end]
        return s 

看答案有的网友的办法，这个应该是最简单，也是解答本题最直接的思路了吧

def trim(s):
    while(s[:1]==' '):
    s=s[1:]
    while(s[-1:]==' '):
    s=[:-1]
    return s