isinstance() and issubclass() return conflicting results

Question

How do you explain isinstance(Hello,object) returns True whilst issubclass(Hello,object) returns False?

>>> class Hello:     pass 

and

>>> isinstance(Hello,object) True >>> issubclass(Hello,object) False >>> a = Hello() >>> isinstance(a,object) True 

Answer 1

The accepted answer is correct, but seems to miss an important point. The built-in functions isinstance and issubclass ask two different questions.

isinstance(object, classinfo) asks whether an object is an instance of a class (or a tuple of classes).

issubclass(class, classinfo) asks whether one class is a subclass of another class (or other classes).

In either method, classinfo can be a “class, type, or tuple of classes, types, and such tuples.”

Since classes are themselves objects, isinstance applies just fine. We can also ask whether a class is a subclass of another class. But, we shouldn't necessarily expect the same answer from both questions.

class Foo(object):     pass  class Bar(Foo):     pass  issubclass(Bar, Foo) #>True isinstance(Bar, Foo) #>False 

Bar is a subclass of Foo, not an instance of it. Bar is an instance of type which is a subclass of object, therefore the class Bar is an instance of object.

isinstance(Bar, type) #>True issubclass(type, object) #>True isinstance(Bar, object) #>True 

Answer 2

It's because you are using old-style classes so it doesn't derive from object. Try this instead:

class Hello(object):     pass  >>> issubclass(Hello,object) True 

Old-style classes are deprecated and you shouldn't use them any more.

In Python 3.x all classes are new-style and writing (object) is no longer required.