Function of symbolic array elements

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I want to create a function like this:

def f(A,B):
    return [A[1]*B[1],A[0],B[2]]

However, the thing that the function is supposed to return is calculated in an earlier part of the program. Since Sagemath has a problem with symbolic indices, I have previously defined A and B as follows:

Nf=5
B =[0 for j in range(Nf+1)]
A =[0 for j in range(Nf+1)]
for j in range(Nf+1):
    A[j]=var('a_'+str(j))
    B[j]=var('b_'+str(j))

The thing that the function should return is calculated in another part of the program. Suppose that it is something like this (evaluated from a separate subroutine):

temp=[a_1*b_1, a_0, b_2]

So my question is: how do I turn this temp into a function similar to f, and the second question: the matrix element references are replaced by variable names. Even if I define a function for temp as it is, I will have to define a huge number of input variables f(a_1, b_1, a_0, b_2, ...) for the function whereas if I could just replace the variables a_1 with A[1], etc., this would have enabled me to use f(A,B) making the function definition so much more compact. How can I achieve this?