利用切片操作,
实现一个trim()函数,去除字符串首尾的空格,不调用str的strip()方法#注意首尾可能不止一个空格def trim(s): if not isinstance(s,str): return 'You must input a string' # elif ========== and s[:-1] != ' ':错误 理解切片索引! elif s[:1] != ' ' and s[-1:] != ' ': return s elif s[:1] == ' ': return trim(s[1:]) else: return trim(s[:-1])#测试: if trim('hello ') != 'hello': print('测试失败!')elif trim(' hello') != 'hello': print('测试失败!')elif trim(' hello ') != 'hello': print('测试失败!')elif trim(' hello world ') != 'hello world': print('测试失败!')elif trim('') != '': print('测试失败!')elif trim(' ') != '': print('测试失败!')else: print('测试成功!')