python version of javascript's arguments object - does it exist?

Question

In JavaScript each function has a special arguments predefined objects which holds information about arguments passed to the function call, e.g.

function test() {
  var args = Array.prototype.slice.call(arguments);
  console.log(args);
}

arguments can be easily dumped to a standard array:

test()
// []

test(1,2,3)
// [1, 2, 3]

test("hello", 123, {}, [], function(){})
// ["hello", 123, Object, Array[0], function]

I know that in Python I can use standard arguments, positional arguments and keyword arguments (just like defined here) to manage dynamic parameter number - but is there anything similar to arguments object in Python?

No. Like you said, the closest thing is varargs like *args and **kwargs, but those only give you "extra" arguments, not all arguments. There is somewhat less need for arguments in Python because (unlike Javascript) it's not possible to call a function with the wrong number of arguments (i.e., if a function requires two arguments, calling it with just one will give an error). What do you want to accomplish that makes you want to use something like arguments? — BrenBarn
– BrenBarn, Commented Jul 10, 2013 at 22:06
@BrenBarn I was trying to implement all memoization techniques in python (basing on javascript patterns). In JS you make heavy use of arguments, e.g. you can make a standard memoize function with one parameter (which is a function to be memoized) which will return closured memoized function. This is done using arguments, as you can see here (see chapter automatic memoization). — ducin
– ducin, Commented Jul 10, 2013 at 22:09
Instead of trying to copy JavaScript patterns, look around for examples of memoization in Python. In Python you can make a memoize decorator which can be used similarly to the sort of JS function you describe. Googling "Python memoize" will give you lots of ideas. — BrenBarn
– BrenBarn, Commented Jul 10, 2013 at 22:11
Anyway, in Python there's nothing like arguments, as I can see. Thanks. — ducin
– ducin, Commented Jul 10, 2013 at 22:13
Fortunately, I found a duplicate of this question: Get a list/tuple/dict of the arguments passed to a function? — Anderson Green
– Anderson Green, Commented Jul 18, 2013 at 23:01

anijhaw · Accepted Answer · 2013-07-10 22:14:06Z

2

It doesnt exist as is in python but you can call locals() as the first thing in the function and at that point it should only have the arguments

>>> def f(a,b):
...    args = locals()
...    for arg, value in args.items():
...        print arg, value
...    return a*b
...

answered Jul 10, 2013 at 22:14

anijhaw

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1 Comment

BrenBarn Over a year ago

That is true, but if the function has varargs you'll just get them as a tuple/dict, not combined "flat" with the regular arguments.

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