python 切片实现trim()

def my_trim(s):
    while True:
        if(str.startswith(s,' ')):#字符串以空格开头
            s = s[1:]
        elif(str.endswith(s,' ')):#字符串以空格结尾
            s = s[:-1]
        else:
            break
    return s

if(my_trim('    hel lo     ') == 'hel lo'):
    print('you are great!')
else:
    print('please change you mind ')

方法二：

思路：循环判断第一个字符，以及最后一个字符是否是空格

def my_trim_demo(s):
    while(True):
        if(s[:1]!=' ' and s[-1:] != ' '):
            return s
        elif s[:1] == ' ' :
            s = s[1:]
        elif s[-1:] == ' ':
            s = s[:-1]

print(my_trim_demo(' hello world   ') == 'hello world')