python - 如何描述一个 Python 对象，属性、标识、类型和值之间的关系是什么？

Question

(关于 Python 3.2)

我试图按照以下方式发表声明:

In Python, an object is...

根据文档(http://docs.python.org/py3k/reference/datamodel.html#objects-values-and-types):

Every object has an identity, a type and a value

但是属性在哪里呢？如果我做类似 a = 3; print(a.__class__) 的事情我得到 <class 'int'>我假设这是对象的类型 a引用，意味着“类型”是对象的“属性”。所以从这个意义上说，我们可以说一个对象拥有的一组足够的“东西”就是它的身份、值(value)和属性。但是，查看使用 dir(a) 的属性，我没有看到任何类似身份的东西(即使我知道 id() 函数会告诉我该信息)。

所以我的问题是，以下任何最小陈述是否足以描述 Python 对象的概念？

1. In Python an object has attributes, of which always include an identity, type and value.

2. In Python an object has an identity and attributes, of which always include its type and value.

3. In Python an object has an identity, value and attributes, of which always include its type, among other things.

如果没有，谁能给我一个传达对象的关系属性、标识、类型和值的定义？

(我希望第 1 条为真。:P)

Answer 1

虽然您可以通过属性访问对象的类型，但它的类型不仅仅是一个属性——类型定义了对象在具有任何属性之前是如何创建的。仅凭这一事实，这些陈述都不足以描述 Python 对象。

我会这样说:

In Python, everything is an object.

An object is a block of information, which has a type, which defines its creation and how it interacts with other objects, an identity, which differentiates it from all other objects, and a value, which is the information in the block. Attributes are other objects associated with a given object, including the object that is its type.

然后您应该给出一些人们可能不认为是对象的示例，例如函数。

关于“什么是对象”的段落可以在 Dive Into Python 中找到:

Everything in Python is an object, and almost everything has attributes and methods. All functions have a built-in attribute __doc__, which returns the doc string defined in the function's source code. The sys module is an object which has (among other things) an attribute called path. And so forth.

Still, this begs the question. What is an object? Different programming languages define “object” in different ways. In some, it means that all objects must have attributes and methods; in others, it means that all objects are subclassable. In Python, the definition is looser; some objects have neither attributes nor methods (more on this in Chapter 3), and not all objects are subclassable (more on this in Chapter 5). But everything is an object in the sense that it can be assigned to a variable or passed as an argument to a function (more in this in Chapter 4).