python 允许对函数参数和返回值类型进行标注，但实际上并不起任何作用，只是看起来方便。

def test(x:int,y:int)->int:
    ''' x and y must be integers,return an integer x+y'''
    assert isinstance(x,int),'x must be integer'
    assert isinstance(y,int),'y must be integer'
    z=x+y
    assert  isinstance(z,int),'must return an integer'
    return z
test(1,2.0)