学以致用：用切片和递归解答

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#1 Created at ... [Delete] [Delete and Lock User]

def trim(s): if s[:1]==' ': #注意，必须这么写，写成s[0]会在边界条件的时候出错，因为空字符串没有s[0]。但是却可以进行切片操作。 return trim(s[1:]) if s[-1:] == ' ': return trim(s[:-1]) return s

#2 Created at ... [Delete] [Delete and Lock User]

空字符串是考虑范围内么

我是这样写的

def trim(s): if s[0] == ' ': s = s[1:] if s[-1] == ' ': s = s[:-1] return s

#3 Created at ... [Delete] [Delete and Lock User]

def trim(s): while 1: if s[0] == ' ': s = s[1:] if s[-1] == ' ': s = s[:-1] if s[0] != " " and s[-1] != " ": break return s 你这个我加了个死循环就可以了，