用可选参数定义函数

Question

Hi I'm trying to understand how to implement optional arguments in a python function. For example, in the basic function below

def Ham(p,*q):
    if q:
        print p+q
    else:
        print p

Ham(2)


Ham(2,3)

I expect Ham(2) to return '2' which it does, however Ham(2,3) gives an error.

EDIT: Many thanks. Many of your answers were useful.

Answer 1

In your particular example, I think you mean to do:

def Ham(p,q=None):
    if q:
        print p+q
    else:
        print p

That is, give q a default value of None and then only calculate p+q if a q is provided. Even simpler would be:

def Ham(p,q=0):
    print p+q

Answer 2

Using *q you are specifyng a list of arguments not known until runtime and python expecting q to be a tuple, it means you can call Ham like below:

Ham(1, 2) # q = (2,)
Ham(1, 2, 3) # q = (2, 3)
Ham(1, 2, 3, 4) # q = (2, 3, 4)

Insidia of Ham function you have to treat q as a tuple, I mean, q[0] rather than q. You can have a look to this link to have a better idea.