What is the purpose of subclassing the class “object” in Python?

Question

All the Python built-ins are subclasses of object and I come across many user-defined classes which are too. Why? What is the purpose of the class object<

Answer 1

Short answer: subclassing object effectively makes it a new-style class (note that this is unnecessary since automatic in Python 3.x)

For the difference between new style classes and old style classes: see this stackoverflow question. For the complete story: see this nice writeup on Python Types and Objects.