Variable args and keyword only args in a function

Question

I was going thru PyTorch and found function signatures like

 torch.zeros(*size, *, out=None, dtype=None, layout=torch.strided, device=None, requires_grad=False) → Tensor

Here the args after * are keyword only args and the size is a variable number of args.

My questions are

1. When I try to define a function in similar lines

def function(*a, *, e=0, f=0):
    print (a, e, f)

function(1, e = 5, f = 6)

I get the following error

 File "main.py", line 2
    def function(*a, *, e=0, f=0):
                     ^
SyntaxError: invalid syntax

2. Also torch.zeros accepts size as keyword. How is this possible ?

torch.zeros(size=(2,3))

AFAIK only these 2 should work

torch.zeros((2,3))
torch.zeros(2,3)