def a(arg):
    print('a %s' % arg)

def b(arg):
    print('b %s' % arg)

def c(arg):
    print('c %s' % arg)

def test_function(func_to_call):
    a_dict = {
    'a': 2,
    'b': 3,
    'c': 4,
    }

    exec('%s(%s)' % (func_to_call, a_dict.get(func_to_call)))

test_function('a')
test_function('b')
test_function('c')