I just read
 https://docs.python.org/3/reference/compound_stmts.html#function-definitions

The item parameter_list is defined as: 

parameter_list            ::=  defparameter ("," defparameter)* "," "/" ["," [parameter_list_no_posonly]] | parameter_list_no_posonly

This definition states that the "," "/" after ("," defparameter)* are mandatory. But this is not true in Python 3.8, because you can define a function as 

def f(a):
    pass

Did I miss something?

> Did I miss something?

Yep, what you are missing is that the rule is really:

(defparameter ("," defparameter)* "," "/" ["," [parameter_list_no_posonly]]) | (parameter_list_no_posonly)

which means that is either 

defparameter ("," defparameter)* "," "/" ["," [parameter_list_no_posonly]]

or

parameter_list_no_posonly

and for the def(a): pass case the corresponding rule is parameter_list_no_posonly (check the rest of the specification).

Do you think that adding these explicit parentheses would help with help making this more clear?

Thanks Pablo, 

sorry, I was just stupid.

> Do you think that adding these explicit parentheses would help with help making this more clear?

Maybe. I read the BNF documentation the first time today, but since it's not intended for beginners, I think it's clear enough.

How should we continue with this issue? I don't really see any closing button or the like.