How to write a python function that adds all arguments?

Question

I'd like to write a python function which adds all its arguments, using + operator. Number of arguments are not specified:

def my_func(*args):
    return arg1 + arg2 + arg3 + ...

How do I do it?

Best Regards

Ernestoernestus

When using *args then args is a list of all arguments passed. – Sodom

@JoachimPileborg: A tuple, to be precise. – Laurenelaurens

If this is a followup to How to find the list in a list of lists whose sum of elements is the greatest? then you need to specify what kind of input this function will take. Your question, as it now stands, will not get you any more helpful answers than what I already gave you there. – Mussel

But it doesn't matter what the input is, it should just add arguments using + operator. – Ernestoernestus

Well, then what's the problem with Python's built-in sum? That's precisely what it does. – Heidt

Why don't you tell us what kind of input you have and what kind of output you expect? For integers, sum is unbeatable, but clearly you have different input. – Mussel

@Ernestoernestus I added another solution to my answer which does not use sum and so does what you want. But it would be helpfull if you could say what's wrong with sum in the first place. – Alms

Answer 1

Just use the sum built-in function

>>> def my_func(*args):
...     return sum(args)
...
>>> my_func(1,2,3,4)
10
>>>

---

Edit:

I don't know why you want to avoid sum, but here we go:

>>> def my_func(*args):
...   return reduce((lambda x, y: x + y), args)
...
>>> my_func(1,2,3,4)
10
>>>

Instead of the lambda you could also use operator.add.

---

Edit2:

I had a look at your other questions, and it seems your problem is using sum as the key parameter for max when using a custom class. I answered your question and provided a way to use your class with sum in my answer.

Alms

But I don't want to use sum function. – Ernestoernestus

@Ernestoernestus - why don't you want to? – Prompt

@Prompt perhaps he wants to use the + operator for cases other than numbers. – Semeiology

@HenryGomersall In this case he should simply add the __radd__ method to his class. – Alms

I assume you could reduce with operator.add instead of (lambda (x, y): x + y) in the second case, correct? (Seems correct.) – Corrie

@CorporalTouchy Yes, correct. I also noticed that in my answer already. – Alms

Second answer looks elegant. I'm using this in django orm for getting sum of multiple fields at one time. – Soares

Answer 2

How about this:

def my_func(*args):
    my_sum = 0
    for i in args:
        my_sum += i
    return my_sum

If you don't want to use the += operator, then

my_sum = my_sum + i

Sodom

This is generalised to make it different to sum() by replacing my_sum = 0 with my_sum = args[0] and the loop to be for i in args[1:]. This now works on any list of objects with a sensible __add__ method. – Semeiology

You could also leave the method as it is and implement a sensible __radd__ method in your class. – Alms

@BigYellowCactus If it's not one's own class, then it's likely to be easier to change the function (e.g. strings). – Semeiology

Answer 3

If you definitely won't be using sum, then something like:

def func(*args, default=None):
    from operator import add
    try:
        return reduce(add, args)
    except TypeError as e:
        return default

or functools.reduce in Py3

Goulden

Answer 4

def sumall(*args):
   sum_ = 0
   for num in args:
       sum_ += num
   return sum_

print(sumall(1,5,7))

The output is 13.

Steal