Python 多态与动态绑定

最新推荐文章于 2025-06-27 03:00:00 发布

翻译最新推荐文章于 2025-06-27 03:00:00 发布 · 614 阅读

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#python #多态 #动态绑定

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本文介绍了一个关于几何对象类的设计案例，包括圆形和矩形类的定义及其属性和方法。通过继承和方法覆盖实现了不同几何形状的统一管理和比较。

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# coding: utf-8
class Geometricobject:
    def __init__(self, color = "green", filled = "True"):
        self.__color = color
        self.__filled = filled

    def getcolor(self):
        return self.__color

    def setcolor(self, color):
        self.__color = color

    def isfilled(self):
        return self.__filled

    def setfilled(self, filled):
        self.__filled = filled

    def __str__(self):
        return "color: " + self.__color + \
            " and filled: " + str(self.__filled)

# coding: utf-8
from GeometricObject import Geometricobject
import math

class Circle(Geometricobject):
    def __init__(self, radius):
       Geometricobject.__init__(self)
       self.__radius = radius

    def getRadius(self):
        return self.__radius

    def setRadius(self, radius):
        self.__radius = radius

    def getArea(self):
        return self.__radius * self.__radius * math.pi

    def getDiameter(self):
        return 2 * self.__radius

    def getPerimeter(self):
        return 2 * self.__radius * math.pi

    def printCircle(self):
        print self.__str__() + "radius: " +  str(self.__radius)

    # Override the __str__() method defined in GeometricObject
    def __str__(self):
        return Geometricobject.__str__(self) + " radius: " + str(self.__radius)

from GeometricObject import Geometricobject

class Rectangle(Geometricobject):
    def __init__(self, width = 1, height = 2):
        Geometricobject.__init__(self)
        self.__width = width
        self.__height = height

    def getWidth(self):
        return self.__width

    def setWidth(self, width):
        self.__width = width

    def getHeight(self, height):
        return self.__height

    def setHeight(self, height):
        self.__height = height

    def getArea(self):
        return self.__width * self.__height

    def getPerimeter(self):
        return 2 * (self.__width + self.__height)

    # Override the __str__ method defined in GeometricObject
    def __str__(self):
        return Geometricobject.__str__(self) + " width: " + \
            str(self.__width) + " height: " + str(self.__height)

# coding: utf-8
from CircleFromGeometricObject import Circle
from RectangleFromGeometricObject import Rectangle

def main():
    # Display circle and rectangle properties
    c = Circle(4)
    r = Rectangle(1, 3)
    displayObject(c)
    displayObject(r)
    print "Are the circle and rectangle the same size? " , \
    isSameArea(c, r)

# Display geometric object properties
def displayObject(g):
    print g.__str__()

# Compare the areas of two geometric objects
def isSameArea(g1, g2):
    return g1.getArea() == g2.getArea()

main()

在这个例子中，c是Circle类的一个对象。Circle类是GeometricObject类的子类。str()方法在这两个类中都有定义。因此，在displayObject方法中g应当调用哪个str()方法？g应当调用哪个str()方法由动态绑定决定。
动态绑定的机制如下：假设对象o是类C1,C2,C3,…,Cn(C1是C2的子类，C2是C3的子类，… ,Cn-1 是 Cn 的子类，即Cn是通用的类，C1是最特定的类)的实例。在Python中，Cn是Object类。如果对象o调用一个方法p,那么Python会依次在类C1,C2,…,Cn中查找方法p的实现,直到找到为止。一旦找到一个实现，就会停止查找然后调用这个第一次找到的实现。