Question

Circle类将Point对象作为圆心。为了验证圆形实例的中心是一个Point对象，我在 init 中添加了一个if not isinstance（）语句。当center不是Point对象时，此if语句引发TypeError。

def __init__(self, center=(0,0), radius=1):
        Point.__init__(self,center)
        self.center=center
        self.radius=radius
        if not isinstance(center,Point):
            raise TypeError("The center must be a Point!")

但是，代码似乎接受（x，y）形式的任何元组为Point对象。有没有办法只将Point对象传递给中心，其他任何元组都是TypeError？

所需的输出如下所示：

>>> circle  =   Circle(center=4,    radius=1.5) 
[Traceback...] 
TypeError:  The center  must    be  a   Point!
>>> circle  =   Circle(center=Point(3,4),   radius=2) 
>>> circle.center   =   (3, 4) 
[Traceback...] 
TypeError:  The center  must    be  a   Point!

以下是Point类的代码：

import math
class Point:
    def __init__(self,x=0,y=0):
        self.x = x
        self.y = y
        self.data=[x,y]
    def __getitem__(self, index):
        return self.data[index]
    def __iter__(self):
        yield self.x
        yield self.y
    def __add__(self,other):
        return Point(self.x+other.x,self.y+other.y) 
    def __mul__(self,n):
        return Point(self.x*n,self.y*n) 
    def __rmul__(self,n):
        return Point(n*self.x,n*self.y) 
    @classmethod
    def from_tuple (cls, self=(0,0)):
        return cls(*self)   
    def loc_from_tuple(self,t=(0,0)):
        self.x=t[0]
        self.y=t[1] 
    def __str__(self):
        return "Point at ({0}, {1})".format(self.x,self.y)  
    def __repr__(self):
        return"Point(x={0}, y={1})".format(self.x,self.y)

以下是班级圈

class Circle(Point):
    def __init__(self, center=(0,0), radius=1):
        Point.__init__(self,center)
        self.center=center
        self.radius=radius
        if not isinstance(center,Point):
            raise TypeError("The center must be a Point!")

    def __getitem__(self,item):
        return self.center[item]
    def __str__(self):
        return "Circle with center at ({0}, {1}) and radius {2}".format(self.center.x, self.center.y, self.radius)
    def __repr__(self):
        return "Circle(center=Point({0}, {1}), radius={2})".format(self.center[0],self.center[1],self.radius)
    def __add__(self,other):
        return Circle(
        Point(self.center.x+other.center.x,
        self.center.y+other.center.y),
        self.radius+other.radius)
    @classmethod
    def from_tuple(cls, center,radius):
        return cls(center, radius)
    @property
    def radius(self):
        return self._radius
    @radius.setter
    def radius(self, radius):
        if radius<0:
            raise ValueError('The radius cannot be negative')
        self._radius=radius

This is what I am getting.

Answer 1

这里代码中发生了什么。当你创建一个带有center = Point（一个Point对象）的圆时，你的代码会创建一个Point，因为你写了

，在Point中作为参数

Point.__init__(self,center) # center is a Point object which is not what you want

这不符合中心的默认值（这是一个元组），当你实例化没有中心的Circle对象时，由于元组中心不会传递，这将无效

isinstance(center,Point)

要使用继承，请执行以下操作（同样，不要验证中心是否更有意义）：

class Circle(Point):
    def __init__(self, center=(0,0), radius=1):
        x, y = center
        super(Circle, self).__init__(x, y)
        self.center = center # This is not useful
        self.radius = radius
        if not isinstance(center, tuple):
            raise TypeError("The center must be a tuple!")

    @property
    def center(self): # This if a better way to access the center
        return(self.x, self.y)

验证圆实例的中心是Point对象，而不是元组

1 个答案: