def trim(s): number = 0 for x in s: if x == ' ': number = number + 1

    # 判断是否全为空
if number == len(s):
    return ' '
elif s == ' ':
    return s
else:
    # 判断前面哪里不是空然后截取
    count = 0
    for x in s:
        if x != ' ':
            s = s[count:]
            break
        count = count + 1
    # 判断后面哪里不是空然后截取
    slen = len(s) - 1
    while s[slen] == ' ':
        slen = slen -1
    s = s[:slen+1]
    return s