对 Python 列表中的 __str__ 感到困惑 [英] Confused about __str__ on list in Python

问题描述

我有 Java 背景，我知道 __str__ 有点像 toString 的 Python 版本(虽然我确实意识到 Python 是较旧的语言).

Coming from a Java background, I understand that __str__ is something like a Python version of toString (while I do realize that Python is the older language).

因此，我定义了一个小类以及一个 __str__ 方法，如下所示:

So, I have defined a little class along with an __str__ method as follows:

class Node:

    def __init__(self, id):
        self.id = id
        self.neighbours = []
        self.distance = 0


    def __str__(self):
        return str(self.id)

然后我创建了它的几个实例:

I then create a few instances of it:

uno = Node(1)    
due = Node(2)    
tri = Node(3)    
qua = Node(4)

现在，尝试打印这些对象之一时的预期行为是它的关联值被打印.这也会发生.

Now, the expected behaviour when trying to print one of these objects is that it's associated value gets printed. This also happens.

print uno

收益

1

但是当我执行以下操作时:

But when I do the following:

uno.neighbours.append([[due, 4], [tri, 5]])

然后

print uno.neighbours

我明白

[[[<__main__.Node instance at 0x00000000023A6C48>, 4], [<__main__.Node instance at 0x00000000023A6D08>, 5]]]

我所期望的

[[2, 4], [3, 5]]

我错过了什么?我在做什么其他令人畏缩的事情?:)

What am I missing? And what otherwise cringe-worthy stuff am I doing? :)

推荐答案

Python 有两种不同的方式将对象转换为字符串:str() 和 repr().打印对象使用 str();打印包含对象的列表使用 str() 作为列表本身，但是 list.__str__() 的实现调用 repr()个别项目.

Python has two different ways to convert an object to a string: str() and repr(). Printing an object uses str(); printing a list containing an object uses str() for the list itself, but the implementation of list.__str__() calls repr() for the individual items.

所以你也应该覆盖__repr__().一个简单的

So you should also overwrite __repr__(). A simple

__repr__ = __str__

在类主体的末尾会起作用.

at the end of the class body will do the trick.

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