How to pass arguments to a thread?

I have test() as shown below:

def test(arg1, arg2=None, arg3=None):

Now, I tries to create a thread using test(), and giving it only arg1 and arg2 but not arg3 as shown below:

threading.Thread(target=test, args=(arg1, arg2=arg2)).start()

But, I got a syntax error. How can I solve the error so that I can pass an argument to the thread as arg2?