elif using dictionary but without excecute the values

Hi let's say that I want to replace a large el-ifs statement by a dictionary. A simplify version of this is as follows:

def functionA(a1, a2, a3):

    results = {
        'case1': a2/a3,
        'case2': 1,
        ...
    }
    return results[a1]

so a1 would be a string ('case1' or 'case2' or ...) the problem is in some cases the a3 it maybe 0 so the results dictionary could not be define (in all those cases a1 would not be 'case1'). For instance:

functionA('case2', 1.0, 3.0)
Out[81]: 1
functionA('case2', 1.0, 0.0)
ZeroDivisionError: integer division or modulo by zero

So in the second case I expected 1 but I am getting an error.

A possible solution is:

def functionA(a1, a2, a3):
    results = {
        'case1': str(a2) + '/' + str(a3),
        'case2': str(1),
    }

    return eval(results[a1])

Since I have a multiple cases with complex calculations, is there any better solution?