如何将关键字传递给函数以使用默认参数

Question

What should I pass to use the default value for "name"? I do not want to explicitly pass 'lisa' since it is the default argument and the user might not be aware. But if I pass an variable "name", I have to use a if else clause to pass nothing to the function in order to print"lisa".

def print_name(name='lisa'):
    print name

if name != '':
    print_name(name) 
else:
    print_name()  # print lisa

Answer 1

What you probably want here is to make the function a bit more complicated:

def print_name(name=None):
    if not name:
        name='lisa'
    print name

… so you can make calling it a lot simpler:

print_name(name)

That if not name: will be true whenever name is anything falsey—whether that's the default value of None , or an empty string. That may not be exactly what you want—maybe you want to explicitly set the default value to '' and check if name == '': , for example—but it's usually a good first guess.

---

So:

>>> name = ''
>>> print_name(name)
lisa
>>> name = 'alis'
>>> print_name(name)
alis

… but you can still do this:

>>> print_name()
lisa

… which is presumably the reason you added a default value in the first place.