Pythonic way to have a choice of 2-3 options as an argument to a function

If the point Niklas’ makes in his answer doesn’t hold, I would use a string argument. There are Python modules in the standard library that use similar arguments. For example csv.reader().

sim_func(a, b, c, sim_type="solar")

Remember to give a reasonable error inside the function, that helps people out if they type in the wrong thing.

def sim_func(a, b, c, sim_type="solar"):
    sim_types = ['solar', 'view', 'both']
    if sim_type not in sim_types:
        raise ValueError("Invalid sim type. Expected one of: %s" % sim_types)
    ...