Write a function to calculate the sum of numbers in python, which is called many times as sum (1) (2) (3)

Question

You need to write a function on python that is called an indefinite number of times, each time it takes a number and returns their sum, for example sum (1) (2) (3) == 6. I found the code for javascript, but I did not find how to redefine it in python __str __ method for the function. How can I override a method or is there another solution?

The code I tried to write:

def sum(n):
    total = n
    def f(k):
        nonlocal total
        total += k
        # f.__str__ = lambda : print(total) # no
        return f
    return f

print(sum(1)(2)(3))

This is working javascript code:

function sum(a) {

  let currentSum = a;

  function f(b) {
    currentSum += b;
    return f;
  }

  f.toString = function() {
    return currentSum;
  };

  return f;
}

alert( sum(1)(2) ); // 3
alert( sum(5)(-1)(2) ); // 6
alert( sum(6)(-1)(-2)(-3) ); // 0
alert( sum(0)(1)(2)(3)(4)(5) ); // 15

Can you use a class? Then you can use its `__call__()` method to allow it to be called as a function, and `__str__` for when the final result is printed. — Barmar, Aug 06 '19 at 21:37
You might want to look at this https://stackoverflow.com/questions/22797580/how-to-replace-str-for-a-function — Deepstop, Aug 06 '19 at 21:56
Your javascript function doesn't return the sum, just so you know, it returns a function object, not an Number at all... — juanpa.arrivillaga, Aug 06 '19 at 23:10

score 1 · Answer 1 · answered Aug 06 '19 at 22:03

It is better to use a class instead of an inner function, and return an object of that class. You would then be able to use the magic __call__ method again and again, if you make it return the same object.

def sum(n):
    class Sum(object): 
        def __init__(self, k):
            self.total = k

        def __call__(self, k):
            self.total += k
            return self

        def __str__(self):
            return str(self.total)

        def __repr__(self):
            return str(self)

    return Sum(n)

Output

>>> sum(1)
1
>>> sum(1)(2)
3
>>> sum(1)(2)(3)
6

This doesn't return the sum, btw. – juanpa.arrivillaga Aug 06 '19 at 23:14 — juanpa.arrivillaga, Aug 06 '19 at 23:14

score 0 · Answer 2 · answered Aug 06 '19 at 21:39

0

If the function is going to be used as func(a)(b)(c)(d)(...) why not just use func([a,b,c,d,...]) ? In this case:

sum([a,b,c,d])

answered Aug 06 '19 at 21:39

Messypuddle

412
6
12

The task requires `func (a) (b) (c) (d) (...)`. – IgorRogachov Aug 06 '19 at 21:41
The whole point of the exercise is to learn about higher-order functions. – Barmar Aug 06 '19 at 21:43

score 0 · Accepted Answer · edited Nov 24 '19 at 01:12

0

What about this:

def summ(a):
    current_sum = a

    return lambda x: current_sum + x

print(summ(1)(2))
>>>3

edited Nov 24 '19 at 01:12

geisterfurz007

5,292
5
33
54

answered Nov 23 '19 at 21:34

Alexey Kislitsin

726
7
12

Write a function to calculate the sum of numbers in python, which is called many times as sum (1) (2) (3)

3 Answers3