what is ,*, ?

[Skaperen]

i think i get it now (after reading the PEP).

in def's function prototype, you can have an argument like foo='bar' at a specific position.  when calling that function, you can provide a value either in that same position without a name or in any ending position by name.  all named values must follow all positioned values (a positioned value may not follow a named value ... after named values, positions are ambiguous).  what the * argument does is change the argument list from that point on so that their defined positions do not have a positional meaning ... to provide a value, the call must provide it as name=value (what are typically called "options" even if we make them mandatory).

Output:
lt1/forums /home/forums 3> py3
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=1):
...     return a,b,c
...
>>> f(1,2,3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() takes 2 positional arguments but 3 were given
>>> f(1,2,c=3)
(1, 2, 3)
>>>
lt1/forums /home/forums 4>

this does not provide for a means to have an argument be position-only and have a default value if not provided.  that is already provided for as variable argument lists.

also, there is no means i am aware of that provides for a named argument that has no default value, and as a result of that must be provided in a call as a name=value form.  i propose enabling this by allowing the argument prototype to have arguments to do this in the form name=