Python函数参数传递顺序

Question

Following code is incorrect:

def add(a, b, c):
    return a + b + c
args = (2, 3)

add(a = 1, *args)
TypeError: add() got multiple values for keyword argument 'a'

I've seen some example in python docs , but I still don't know why there's an error, can anybody explain in detail?

Answer 1

When applying the arguments, Python first fills in the positional arguments, then the keyword arguments.

In your specific case, *args is then applied firsts, so the first positional argument is passed 2 , the second is passed 3 . The first argument is a here.

Then the a = 1 is applied, and Python finds that you already applied a value to it.

In other words, Python cannot and will not take positional arguments out of consideration when you use one as a keyword argument. Just because you used a as keyword argument does not make it ineligible as a positional argument.