Incorporated keyword arguments into invocation descriptions so that argument
compatibility can be more broadly tested and restrict accesses accordingly.
1classC: 2deff(self,x,y,z): 3returnz 4 5classD: 6deff(self,a,b,c): 7returnc 8 9defpqr(obj): 10returnobj.f(1,2,r=3)# no corresponding function 11 12c=C() 13d=D() 14 15printpqr(c)# should fail