what is ,*, ?

[snippsat]

It looks like the name of the function is automatically passed as argument b:

No,default argument test is passed.
Name of function is test2

The point is as dvs1 showed.
If use that function without ,*,,and pass in 2 positional argument.

def test1(a, b='test'):
    print(a)
    print(b
     
test1('hello', 'world')

Output:
hello
world

So is allowed to give a argument that is not a keyword argumet.
With ,*,

def test1(a,*, b='test'):
    print(a)
    print(b)
     
test1('hello', 'world')

Output:
Traceback (most recent call last):
File "e:\1py_div\div_code\pos.py", line 32, in <module>
test1('hello', 'world')
TypeError: test1() takes 1 positional argument but 2 were given

So is forced to use keyword argument.

def test1(a,*, b='test'):
    print(a)
    print(b)
     
test1('hello', b='world')

Output:
hello
world