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当类从无继承时，我有一个实例类型的对象。
>>> class A(): pass;
>>> a = A()
>>> type(a)
<type 'instance'>
>>> type(a) is A
False
>>> type(A)
<type 'classobj'>
但是，当我从一个对象继承同一个类时，创建的对象是A类型。
>>> class A(object): pass;
>>> a = A()
>>> type(a)
<class '__main__.A'>
>>> type(a) is A
True
>>> type(A)
<type 'type'>
这背后的逻辑是什么？这是否意味着每个类都应该从对象继承？
最佳答案
在 Python 3 中，这两个是相同的。然而，在 Python 2 中:
class A: pass # old-style class
class B(object): pass # new-style class
来自 New-style and classic classes在文档中:
Up to Python 2.1, old-style classes were the only flavour available to the user. The concept of (old-style) class is unrelated to the concept of type: if
xis an instance of an old-style class, thenx.__class__designates the class ofx, buttype(x)is always<type 'instance'>. This reflects the fact that all old-style instances, independently of their class, are implemented with a single built-in type, called instance.New-style classes were introduced in Python 2.2 to unify classes and types. A new-style class is neither more nor less than a user-defined type. If
xis an instance of a new-style class, thentype(x)is the same asx.__class__.The major motivation for introducing new-style classes is to provide a unified object model with a full meta-model. It also has a number of immediate benefits, like the ability to subclass most built-in types, or the introduction of "descriptors", which enable computed properties.
出于这些原因，最好尽可能使用新式类。旧式类甚至存在于 Python 2.2+ 中的唯一原因是为了向后兼容；在 Python 3 中，旧式类已被删除。
关于python - 为什么从对象继承在 Python 中有所不同？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18345827/