How to determine if a variable is an instance in Python 3? I consider something to be an instance if it has __dict__ attribute.

Example:

is_instance_of_any_class(5)  # should return False
is_instance_of_any_class([2, 3])  # should return Falseclass A:passa = A()
is_instance_of_any_class(a)  # should return True

I have seen messages about using isinstance(x, type) or inspect.isclass(x) but this would give True for the class (A), not the instance.

I think your understanding of what an instance is wrong here, since everything is an object in python, so 5 is an object of class int and [2,3] is an object of class list and so on.

isinstance(x, y) is the way to go if you just want to check if x is an object of y, but if you want to check if x is an object of builtin class or your own custom defined class then you should be checking the existence of __dict__ using hasattr(x, '__dict__').