重写 __repr__ 时出错'TypeError-expected 0 arguments, got 1' [英] Error while rewriting __repr__ 'TypeError-expected 0 arguments, got 1'

问题描述

我在通过弄清楚 __repr__ 的用法来调试以下代码时出错.

I have an error while debugging the following code by figuring out the usage of __repr__.

class node(object):
    def __init__(self, value):
        self.value = value
        self.children = []
    def __repr__(self, level=0):
        ret = "\t"*level+repr(self.value)+"\n"
        for child in self.children:
            ret += child.__repr__(level+1)
        return ret
    def add(self, nod):
        self.children.append(nod)
leaf_1 = [1,4,3]
leaf_2 = [2,5,3]
leaf_3 = [4,4,3]
leaf_4 = [5,5,5]
tree = parent = node(leaf_1)
parent.add(leaf_2)
parent.add(leaf_3)
parent.add(leaf_4) 
print(tree) # no error without this line

每当我输入 print(tree) 时，都会出现错误，但是如果我注释了这一行，则没有错误.如果我将 self.children.append**(nod)** 更改为 self.children.append**(node(nod))**，则不会出错使用 print(tree).

Whenever I put the print(tree), there is an error, but if I commented this line, no error. If I change self.children.append**(nod)** to self.children.append**(node(nod))**, no error while I use print(tree).

Traceback (most recent call last):
  File "C:\Users....tree.py", line 30, in <module>
    print(tree)
  File "C:\Users....tree.py", line 9, in __repr__
    ret += child.__repr__(level+1)
TypeError: expected 0 arguments, got 1

问题:

1. 为什么我会收到错误消息?我在哪里可以看到 1 参数?
2. 为什么它必须使用 self.children.append**(node(nod))**?我完全不明白这背后的逻辑?

1. why did I get the error? where can I see the 1 argument?
2. why it must be using the self.children.append**(node(nod))**? I totally do not understand the logic behind it?

我已经调试并查看了值，但我只能看到变量的更新和关系，我看不到原因.如果有人能向我解释一下，我将不胜感激，谢谢！

I have debugged and watched values, but I can only see the variables' updates and relations, I cannot see the reasons. I much appreciate it if anyone can explain a little bit to me, thanks!

推荐答案

我尝试回答您的问题:

你的第一个错误:

Traceback (most recent call last):
  File "C:\Users....tree.py", line 30, in <module>
    print(tree)
  File "C:\Users....tree.py", line 9, in __repr__
    ret += child.__repr__(level+1)
TypeError: expected 0 arguments, got 1

这是因为在您的班级中，您定义了以下内容:

This is because in your class, you've defined the following:

def __repr__(self, level=0):
        ret = "\t"*level+repr(self.value)+"\n"
        for child in self.children:
            ret += child.__repr__(level+1)
        return ret

level=0 代表一个 kwarg 参数.如果需要使用该参数，则需要执行以下操作:ret += child.__repr__(level=level+1)

The level=0 represents a kwarg argument. If you need to use that argument, you need to do the following: ret += child.__repr__(level=level+1)

如果你只想做 ret += child.__repr__(level+1)，你的 __repr__ 定义应该是:

If you had wanted just to do ret += child.__repr__(level+1), your __repr__ definition should be:

def __repr__(self, level):

然后调用 ret += child.__repr__(level+1) 不会报错.

Then calling ret += child.__repr__(level+1) would not give an error.

现在，关于 self.children.append**(node(nod))**;

如您的代码所述，leaf_* 是列表.

As stated in your code, leaf_* are lists.

leaf_1 = [1,4,3]
leaf_2 = [2,5,3]
leaf_3 = [4,4,3]
leaf_4 = [5,5,5]

您的 def add(self, nod): 方法只是将 nod 的值附加到 self.children 列表中.但是，在所有附加之后， self.children 将只是一个列表列表，而不是您在执行以下操作时所期望的节点列表:

Your def add(self, nod): method just appends the value of nod to the self.children list. However, after all that appending, self.children would be just a list of lists, not a list of nodes which is what your expecting when you do the following:

        for child in self.children:
            ret += child.__repr__(level+1)

因为你定义了 Node 对象的 repr 方法，如果每个孩子都是一个 Node 对象，那么上面的方法是有效的；但他们不是.

Since you defined the Node object's repr method, the above would be valid if each child were of a Node object; but they aren't.

这就是为什么当您执行 self.children.append(Node(nod)) 时，实际上是将 Node 类型的实例化对象附加到 self.children领域.

This is why when you do a self.children.append(Node(nod)), you are actually appending instantiated objects of Node type to the self.children field.

总而言之，最终的结果应该是:

So all in all, the final result should be:

class node(object):

    def __init__(self, value):
        self.value = value
        self.children = []

    def __repr__(self, level=0):
        ret = "\t"*level+repr(self.value)+"\n"
        for child in self.children:
            ret += child.__repr__(level=level+1)
        return ret

    def add(self, nod):
        self.children.append(nod)


leaf_1 = [1,4,3]
leaf_2 = [2,5,3]
leaf_3 = [4,4,3]
leaf_4 = [5,5,5]
tree = parent = node(leaf_1)
parent.add(node(leaf_2))
parent.add(node(leaf_3))
parent.add(node(leaf_4)) 
print(tree)

或者你当然可以做你以前做过的事情:

or you can, of course do what you did before:

class node(object):

    def __init__(self, value):
        self.value = value
        self.children = []

    def __repr__(self, level=0):
        ret = "\t"*level+repr(self.value)+"\n"
        for child in self.children:
            ret += child.__repr__(level=level+1)
        return ret

    def add(self, nod):
        self.children.append(node(nod))


leaf_1 = [1,4,3]
leaf_2 = [2,5,3]
leaf_3 = [4,4,3]
leaf_4 = [5,5,5]
tree = parent = node(leaf_1)
parent.add(leaf_2)
parent.add(leaf_3)
parent.add(leaf_4) 

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