迭代的强大威力

# -*- coding: utf-8 -*-
def trim(s):
    if s[:1] == ' ':
        return trim(s[1:])
    if s[-1:] == ' ':
        return trim(s[:-1])
    return s

普通的循环也可以 要点：

• 注a[1:n]表示从1开始到n-1结束

<br>

# -*- coding: utf-8 -*-
def trim(s):
    begin = 0
    end = -1
    length = len(s)
    for i in range(length):
        if s[i] != ' ':
            begin = i
            break
    j = length - 1
    while j >= begin and s[j] == ' ':
        j -= 1
        pass
    end = j
    return s[begin:end+1]