----THE CODE----

class XYZ:
 def FunctionA(self,string):
  # Snip - stuff to parse STRING into PREFIX, CMD, and ARGS
  f = getattr(self,'_on_'+cmd)
  f(prefix,cmd,args)

 def _on_Stuff(self,prefix,cmd,args)
  # Snip


----THE ERROR----
 On the line with f(prefix,cmd,args)
TypeError: _on_Stuff takes 4 arguments (5 given)