### How do I define a homomorphism of a graded commutative algebra?

I am working on implementing morphisms of graded commutative algebras. I have two graded commutative algebra, A with generators <w,x> and B with generators <y,z> . I define H the set of homomorphisms from A to B. Then, I want to define the homomorphisms f such that f(w)=y and f(x)=0 but I get an error:

sage: H = Hom(A,B)
sage: H([y,0])

TypeError: images do not define a valid homomorphism