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Another approach would be to build a 2-dimensional vector space.

First build the base field:

sage: FFq.<a> = GF(2^3) 
sage: FFq
Finite Field in a of size 2^3

We could make a list from this:

sage: list(FFq)
[0, a, a^2, a + 1, a^2 + a, a^2 + a + 1, a^2 + 1, 1]

And we can square the field to get a vector space:

sage: FFq^2    
Vector space of dimension 2 over Finite Field in a of size 2^3

This can be listed too:

sage: list(FFq^2)
[(0, 0), (a, 0), (a^2, 0), (a + 1, 0), (a^2 + a, 0), (a^2 + a + 1, 0), (a^2 + 1, 0), (1, 0), (0, a), (a, a), (a^2, a), (a + 1, a), (a^2 + a, a), (a^2 + a + 1, a), (a^2 + 1, a), (1, a), (0, a^2), (a, a^2), (a^2, a^2), (a + 1, a^2), (a^2 + a, a^2), (a^2 + a + 1, a^2), (a^2 + 1, a^2), (1, a^2), (0, a + 1), (a, a + 1), (a^2, a + 1), (a + 1, a + 1), (a^2 + a, a + 1), (a^2 + a + 1, a + 1), (a^2 + 1, a + 1), (1, a + 1), (0, a^2 + a), (a, a^2 + a), (a^2, a^2 + a), (a + 1, a^2 + a), (a^2 + a, a^2 + a), (a^2 + a + 1, a^2 + a), (a^2 + 1, a^2 + a), (1, a^2 + a), (0, a^2 + a + 1), (a, a^2 + a + 1), (a^2, a^2 + a + 1), (a + 1, a^2 + a + 1), (a^2 + a, a^2 + a + 1), (a^2 + a + 1, a^2 + a + 1), (a^2 + 1, a^2 + a + 1), (1, a^2 + a + 1), (0, a^2 + 1), (a, a^2 + 1), (a^2, a^2 + 1), (a + 1, a^2 + 1), (a^2 + a, a^2 + 1), (a^2 + a + 1, a^2 + 1), (a^2 + 1, a^2 + 1), (1, a^2 + 1), (0, 1), (a, 1), (a^2, 1), (a + 1, 1), (a^2 + a, 1), (a^2 + a + 1, 1), (a^2 + 1, 1), (1, 1)]

So now we can define the function:

sage: def f(x,y):        
....:     return x*y+x^2+y^3
....:

And then apply it to each coordinate pair:

sage: [f(*coords) for coords in FFq^2]
[0, a^2, a^2 + a, a^2 + 1, a, a + 1, a^2 + a + 1, 1, a + 1, a + 1, a^2 + a, 0, a^2 + a, a^2 + 1, a^2 + 1, 0, a^2 + 1, a, a^2 + 1, a^2 + a + 1, a, a^2 + a + 1, 0, 0, a^2, a^2 + a, a^2 + 1, a^2, a^2 + a + 1, a^2 + 1, a^2 + a + 1, a^2 + a, a^2 + a + 1, a^2, a^2, a + 1, a^2 + a + 1, 0, a + 1, 0, a, a + 1, a^2 + 1, a^2 + 1, a^2, a, a + 1, a^2, a^2 + a, a + 1, a, a^2 + a + 1, a^2 + a + 1, a + 1, a^2 + a, a, 1, a^2 + a + 1, a + 1, a^2 + a + 1, a^2 + 1, a^2 + 1, a + 1, 1]

Note that the * syntax here is called argument unpacking. Basically, f(*(2,3,4)) = f(2,3,4).

To summarize, an alternative approach would be:

FFq.<a> = GF(2^3)
def f(x,y): 
    return x*y+x^2+y^3

[f(*coords) for coords in FFq^2]