What's a good way to keep track of class instance variables in Python

class foo:
  a = 0 #class variable

  def __init__(self):
    self.b = 0 #instance variable

d = {'command1' : func1, 'command2': func2, 'command3' : func3}
#then somewhere else use this list to dispatch
#given a string `str`
func = d[str]
func() #call the function!