The function name in the docstring should match the name of the function (get_activation_fn_with_deriv).
Change:
>>> relu, relu_deriv = activation_fn_with_deriv('relu')
to:
>>> relu, relu_deriv = get_activation_fn_with_deriv('relu')
Since all the function names in the available_fn list are already lower-case, there is no need to loop through them and call lower(). The raise statement can be simplified, also shortening a long line:
raise ValueError(f'Specified activation function not available. Choose from: {available_fn}')