Question

I am learning to use positional arguments in python and also trying to see how they work when mixed up with default arguments:-

def withPositionalArgs(ae=9,*args):
    print 'ae= ', ae
    print 'args = ', args


a=1
b=2
c=[10,20]

withPositionalArgs(a,b,c)

This gives me the output:

ae=  1
args =  (2, [10, 20])

As you can see, a is considered to be a value passed for ae, and b as well as c are considered to be the positional arguments.

So, I am now trying to assign 10 for ae while calling withPositionalArgs:

withPositionalArgs(ae=10,b,c)

But, I can not do it. I get the error:

SyntaxError: non-keyword arg after keyword arg

My question is:

Am I doing correctly? Is having default argument allowed or a good practice to use before positional arguments in python functions?

Answer 1

In Python2, you are not allowed to put arguments which have a default value before positional arguments.

The positional arguments must come first, then the arguments with default values (or, when calling the function, the keyword arguments), then *args, and then **kwargs.

This order is required for both the function definition and for function calls.

In Python3, the order has been relaxed. (For example, *args can come before a keyword argument in the function definition.) See PEP3102.