矩形OOP /类

Question

我需要创建一个矩形数据类和一个可执行程序来测试它。

这是我正在处理的完整问题：

在可执行文件的主要功能中：

• 提示用户输入矩形的长度和宽度。

• 创建一个新的Rectangle实例，其中包含由尺寸输入的尺寸 用户。

• 验证上述步骤，使用它们打印两个尺寸 各自的“getter”方法。

• 通过打印矩形区域来测试area（）方法，精确到两个 小数位。

• 通过打印矩形周长来测试perimeter（）方法， 精确到小数点后两位。

• 将长度更改为22.345并将宽度更改为15.789。

• 再次测试area（）和perimeter（）方法。你应该得到 结果显示在样本输出中。*

我的问题是，类文件必须与可执行文件位于同一文件夹中吗？

如果有人想提供剩下的提示，请这样做。这就是我对矩形类的看法：

class Rectangle:

    def __init__(self, length, width):
        self.__length = length
        self.__width = width

    def set_length(self, length):
        self.__length = length 

    def set_width(self, model):
        self.__width = width 

    def get_length(self):
        return self.__length 

    def get_width(self):
        return self.__width

    def get_area(self):
        return self.__getwidth() * self.getlength()

    def get_perimeter(self):
        return self.__getwidth() * 2 + getlength() * 2

Answer 1

你的班级看起来或多或少都不错。但是，在您发布的第一张描述类设置的图片中，get_area()和get_perimeter()的名称应该只是area()和perimeter()。还有一些其他小错字，因为@PaulCornelius提到会导致错误。

您的“可执行文件”，即调用Rectangle类方法的文件可以在另一个文件中，但不需要。例如：

class Rectangle:
    #all of the above stuff
r= Rectangle(10,20)
print r.get_area()

可以正常工作，打印矩形区域。

否则，您可以创建一个包含import rectangle的新文件来导入Rectangle课程。这确实需要它在同一个文件夹中（或者你必须配置Python，因此它知道在哪里寻找模块）。

创建实际调用方法的脚本是验证事情正常行为的最佳方法，并可能提供有关如何修复它们的提示。例如，尝试在get_area()上调用Rectangle会导致错误（因为__getwidth()未在任何地方定义，但get_width()是。）

Answer 2

通过对拼写错误进行一些更正，您可以将类定义放在主程序中：

class Rectangle:

    def __init__(self, length, width): # this initializes the object with the given parameters
        self.__length = length # assign length
        self.__width = width # assign width

    def set_length(self, length): # this method allows us pass the Rectangle object a value and set the object's length to the given value
        self.__length = length # assign length

    def set_width(self, width): # had 'model' here # same thing, for width
        self.__width = width # assign width

    def get_length(self): # this method does one thing...
        return self.__length # return the Rectangle object's length

    def get_width(self): # and same for width
        return self.__width

    def get_area(self): # this actually does something: multiplies width by height and returns that value
        return self.get_width() * self.get_length() # underscores were wrong

    def get_perimeter(self): # similarly, this adds double the length to double the width and returns that value
        return self.get_width() * 2 + self.get_length() * 2 # underscores were wrong, missing self

def main(): # our main program, which will test our Rectangle class
    length = float(input('Length? ')) # request a length and turn that string into a float
    width = float(input('Width? ')) # request a width and turn that string into a float
    rectangle = Rectangle(length, width) # create a new Rectangle object with the given length and width
    print(rectangle.get_length(), rectangle.get_width()) # print the object's length and width, using the getters
    print(round(rectangle.get_area(), 2)) # round the area to 2 places and print it
    print(round(rectangle.get_perimeter(), 2)) # round the perimeter to 2 places and print it
    rectangle.set_length(22.345) # calls the Rectangle object's length setter and passes it a new value, which will set the object's length to the given value
    rectangle.set_width(15.789) # same for width
    print(round(rectangle.get_area(), 2)) # print the area again to see the new value
    print(round(rectangle.get_perimeter(), 2)) # print the perimeter again to see the new value

main() # call our main method - without this, nothing happens

注意：Getters和setter不属于Python程序。一个合适的Python Rectangle看起来像这样：

class Rectangle:
    def __init__(self, length, width):
        self.length = length # no need to mask these by starting the names with _
        self.width = width

    @property # this lets us call this method without parentheses - it'll look like an ordinary attribute, but it's really calling a method
    def area(self):
        return self.length * self.width

    @property
    def perimeter(self):
        return 2*(self.length + self.width) # the original has 2 multiplications and 1 addition, while this has 1 multiplication and 1 addition - negligible, but it's good to see this sort of thing once in a while in case you have to optimize something at some point

这将被用作：

>>> a = Rectangle(3.2,5.1)
>>> a.area
16.32
>>> a.perimeter
16.6
>>> a.length=2
>>> a.area
10.2
>>> a.perimeter
14.2
>>> a.length
2

但请注意：

>>> a.area = 3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute

这就像rectangle.get_area() = 3那样有意义 - 即没有。