Why positional arguments need to be specified before keyword arguments in Python?

Question

I understand passing positional arguments first and then passing the keyword arguments is a rule in python.

And that's why these are wrong:

def fun(x,y):
    print(x,y)
 
fun3(y=4,3)

SyntaxError: positional argument follows keyword argument

and this is wrong too.

def fun2(**kwargs,*args):
  File "<stdin>", line 1
    def fun2(**kwargs,*args):
                     ^
SyntaxError: invalid syntax

Python strictly checks that I am passing positional arguments first. What I don't understand. Why?

Isn't this intuitive:

def test(x,y,z):
    print(x,y,z)

and then calling the function as

test(z=3,1,2)

should first assign keyword argument z's value 3 and then sequentially assign 1 and 2 to the remaining unassigned variables x and y respectively.

It's not even that python doesn't check if the variable is already assigned or not, because the following gives an error like:

def test2(x,y):
    print(x,y)
 
test2(1,x=1)
TypeError: test2() got multiple values for argument 'x'

Got multiple values for x. So python definitely knows which variable have already received the values. Why can't it then just check for which variables haven't received the values and then assign them those positional argument values sequentially.

I am making notes for my reference and I am stuck while writing anything about the logic behind this behavior of python.

Python *could* have been designed to work the way you want, but it wouldn't actually make Python a *better language* to do so. It would just be more confusing and bug-prone. — user2357112, Feb 14 '21 at 10:13

score 0 · Answer 1 · answered Feb 14 '21 at 10:22

Python functions follow the order of the arguments when it is defined and assigns the value to them in the same order when we call the function. Doing what you want to do will confuse it like you tried to do in the second problem (TypeError: test2() got multiple values for argument 'x').

As we get errors by doing so, it is still better but if such feature had been added to python, there maybe some more bugs (especially which won't produce errors). E.g, assigning a value to an argument which is wrong as per our logic.

Actually they are defined by their name. Positional args are called so because they are dependent of their positions and same for keyword args as they include a keyword equated with its value — Irfan wani, Feb 14 '21 at 10:36

score 0 · Accepted Answer · edited Feb 16 '21 at 07:06

See it seems your argument is valid.

But I like to point out when you said, "Isn't this intuitive:"

Tell me any other object oriented language where you have seen this, and is quite popular.

So the thing is python is popular because it is very easy to adapt to,

I don't know about you but I switched to python recently from C, and there I use to

create functions like length, reverse, sort etc. in python the exact most common names are present of the similar function. It is so easy to adapt, unlike other language where they change name or insert these functions hidden in some utils class like java.

To answering your question. Like other say it will increase complexity.

And this is why other popular object oriented language didn't adopt it.

And so since its not available in other popular language.

Python didn't adopt it, cause it would make adapting to python difficult. And also due to underlying reason that it would make things complex.

"Isn't this intuitive:" for me, politely, NO, it is not intuitive.

If I pass argument at position 0 in function call, it would expect it to go to position 0 argument in function defination. Cause That's how I did in C. And I believe cause that's how its done in most object oriented language.

Why positional arguments need to be specified before keyword arguments in Python?

2 Answers2