what is ,*, ?

[Skaperen]

to add to the above:

Output:
Python 3.5.2 (default, Nov 17 2016, 17:05:23)
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(a,*,b,c,d,e,f):
...   return
...
>>> f(1,b=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() missing 4 required keyword-only arguments: 'c', 'd', 'e', and 'f'
>>>