如何在python中设置__contains__方法？ [英] How do you set up the __contains__ method in python?

问题描述

我无法理解如何在我的课程中正确设置包含方法。我知道它会自动使用操作符in当你调用它，我只是不认为我理解如何正确设置它。

I'm having trouble understanding how to properly set up a contains method in my class. I know it automatically uses the operator "in" when you call it, i just don't think I understand how to set it up correctly.

我必须使用它以查看anotherCircle是否包含在特定圆（两个来自用户的输入）中。教授为我们做了两种不同类型的方法。

I have to use it to see if anotherCircle is contained within a specific circle (both input from the user). The prof had us do two different types of methods for this.

第一个我没有问题，或多或少了解它在做什么，它如下：

The first one I have no problems with and more or less understand what it is doing, It is as follows:

def contains(self, circle2d):
  dist = math.sqrt((circle2d._x - self._x)**2 + (circle2d._y - self._y)**2) #Distance of second circle's coords from the first circle's coords
  if dist + circle2d._radius <= self._radius:
     return True

但是，接下来的方法应该做同样的事情， strong>包含方法，以便我们可以在主函数中使用 in 来调用它。我所有的是这样：

However, the next method, which is supposed to do the same thing, uses the contains method so that we can call it with in in the main function. All I have is this:

def __contains__(self, anotherCircle):
    if anotherCircle in self:
        return True 

当我试图运行这个时，我得到了多个错误。我想我错过了自我，但我不知道什么？有人可以尝试向我解释，当你编写包含方法时，你需要做什么？

I get multiple errors when I try to run this. I think i'm missing something on self, but I'm not sure what? Could someone please try to explain to me what exactly you need to do when you're writing a contains method such as this?

推荐答案

__包含对象上的__ 方法不会 c>;

The __contains__ method on an object doesn't call in; rather, it is what the in operator calls.

当你写

if circle1 in circle2:

python解释器将会看到 circle2 是一个Circle对象，并且将查找为其定义的 __包含__ 方法。它实质上会尝试调用

The python interpreter will see that circle2 is a Circle object, and will look for a __contains__ method defined for it. It will essentially try to call

circle2.__contains__(circle1)

这意味着您需要写 __包含__ 方法，而不使用 c $ c>，否则你将编写一个从不结束的递归方法。

This means that you need to write your __contains__ method without using in, or else you will be writing a recursive method that never ends.

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