Problem adding triples in rdflib.store.IOMemory

Question

Whenever I try to add triple into the store using following code it gives me following error. Could you please help me in this regard. Thanks in advance.

store = plugin.get('IOMemory',Store)()
store.add((abc, FOAF['knows'],def))

Error:

Traceback (most recent call last):
  File "C:\Python27\internetcode.py", line 114, in <module>
  store.add((abc, FOAF['knows'],def))
TypeError: add() takes at least 3 arguments (2 given)