[Python] How to distinguish between an instance of a class and normal datatype...

In Python I am trying to integrate through an object wo (user defined) and wo.obj is another user defined object how do I tell it is an instance of a class rather than normal data types?

type(wo.obj)
<class '__main__.test'>

type(wo.obj) is types.InstanceType
False

type(wo.obj) is types.ClassType
False

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