unbound method must be called with class instance 1st argument ??

[Dr Mike Lance]

I was trying out the following example from the tutorial...

class Bag:
    def __init__(self):
        self.data = []
    def add(self, x):
        self.data.append(x)
    def addtwice(self, x):
        self.add(x)
        self.add(x)

I stored this in bags.py and then tried the following...
>>> import Bags
>>> b = Bags.Bag
>>> b.add(1)

This last line resulted in an error message which was...

Traceback (innermost last):
  File "<interactive input>", line 1, in ?
TypeError: unbound method must be called with class instance 1st argument
>>>

It looks like the instance attribute data does not exist?
What is the cause of this problem and what is the solution?

TIA