Question

To determine the class, I can do so:

class A: pass    
a = A

type(A) is type #True

or:

import inspect
inspect.isclass(A) 

But how to determine the type of class instance, not knowing the class name?

Something like this:

isinstance(a, a.__class__.__name__)
#TypeError: isinstance() arg 2 must be a type or tuple of types

I found one solution, but it does not work with Python 3x

import types

class A: pass
a = A()

print(type(a) == types.InstanceType)
#AttributeError: 'module' object has no attribute 'InstanceType'

Solution:

if '__dict__' in dir(a) and type(a) is not type:

Answer 1

type(a) is the type of the instance, i.e., its class. a.__class__ is also a reference to the instance’s class, but you should use type(a).

types.InstanceType is only for old-style classes in versions of Python pre-3.0, where all instances had the same type. You should be using new-style classes (derived from object) in 2.x. In Python 3.0, all classes are new-style classes.