Function to sum multiple numbers

Question

I'm new to python and I started learning to execute function. And I started adding numbers but I could only sum two numbers and if I wanted to sum more, it would require I edit the program. Here's my code

def sum(num1,num2):
    return num1+num2

a=5
b=7
c=sum(a,b)
print (c)

Now I want to create a function to sum any amount of number you want without Editting the codes. Here was what I did:

def sum(num1,num2):
    return num1+num2
a=int(input("what is the number you want to add?: "))
ask="yes"
while(ask=="yes"):
  b=int(input("what is the number you want to add?: "))
  c=sum(a,b)
  a=c
  ask=input("do you want to add another number?: ")
else:
    c=a
    print (c)

This worked but i think there should be an easier way to do this with a function... right? Thanks for your help!

TerryA · Accepted Answer · 2018-04-26T12:55:31.020

9

You want to have an *args parameter in your function so that you may take as many inputs more than 1:

def summ(num1, *args):
    total = num1
    for num in args:
        total = total + num
    return total

What the *args means is you can pass through as many arguments as you want:

>>> summ(1, 2, 3)
6
>>> summ(1, 2, 3, 4, 5, 6, 7)
28

args is an iterative object: we iterate through it and add each of its numbers to a total which we then return.

edited Apr 26 '18 at 12:55

answered Apr 26 '18 at 12:46

TerryA

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`total = total + num` => `total += num` – Jean-François Fabre Apr 26 '18 at 12:50
@Jean-FrançoisFabre Sure :P. I always liked the clarity of `total = total + num` – TerryA Apr 26 '18 at 12:51
so why not `return num1 + sum(args)` ? – Jean-François Fabre Apr 26 '18 at 12:51
4

@Jean-FrançoisFabre I assumed the OP was learning about writing functions, not about what built-ins existed. Using `sum()` would defeat the purpose of the whole question! – TerryA Apr 26 '18 at 12:52
for lists, don't to `list1 = list1 + list2` because of the quadratic effect. It should be painless for integers, though. – Jean-François Fabre Apr 26 '18 at 12:53
1

@Jean-FrançoisFabre True, yes. But that's where `list.extend()` comes handy ;) – TerryA Apr 26 '18 at 12:54
Whatever you might might like, not using augmented assignment where it makes sense smells like beginner code (and it might also prevent some optimizations to work as expected). – bruno desthuilliers Apr 26 '18 at 13:08

akshat · Answer 2 · 2018-04-26T12:55:37.483

3

you can use variable args to accept any number of arguments

def my_sum(*args):
    total = 0
    for val in args:
        total += val
    return total

You can also use python's in-built sum() to add them:

def my_sum(*args):
    return sum(args)

>>> my_sum(1,2,3,4)
10
>>> my_sum(1,5,6,7.8)
19.8

edited Apr 26 '18 at 12:55

answered Apr 26 '18 at 12:52

akshat

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jpp · Answer 3 · 2018-04-26T12:54:25.830

First thing to note is Python has a native sum function. Use this instead for simple calculations, don't overwrite it with your own.

But to learn more about Python, you may wish to use functools.reduce, which applies a function of two arguments cumulatively to the items of a sequence.

from functools import reduce

def mysum(*nums):
    return reduce(lambda x, y: x+y, nums)

a, b, c = 1, 2, 3

res = mysum(a,b,c)  # 6

This can be incorporated into your logic by building a list which then feeds your function:

lst = []

lst.append(int(input("what is the number you want to add?: ")))

ask = "yes"

while ask == "yes":
    lst.append(int(input("what is the number you want to add?: ")))
    ask = input("do you want to add another number?: ")
else:
    res = mysum(*lst)
    print(res)

Why use a module just to add tuple elements!! sum() function can be used here. — eiram_mahera, Apr 26 '18 at 12:48
@eiram_mahera, Because this user wants to **learn about Python**. That's why. — jpp, Apr 26 '18 at 12:50

Masha Kereb · Answer 4 · 2018-04-26T13:15:41.177

There are several ways how to add a different quantity of numbers. First of all, you can just use a list and built-in function sum: sum([1, 2, 3])

If you wouldn't like to use a list, try to write a custom wrapper on built-in sum function (it is good practice to not override the built-in names):

def my_sum(*args):
    return sum(args)

my_sum(1, 2, 3)

Also, such usage is possible:

my_sum(2) # result is 2
my_sum()  # result is 0

But if you want a function, that takes minimum two arguments, try following:

def my_sum(num1, num2, *args):
    return num1 + num2 + sum(args)

my_sum(1, 2, 3)

Laurent H. · Answer 5 · 2018-04-26T15:24:03.967

0

I suggest you an update based on following explanations:

I recommend to avoid using the name sum for a user-defined function because this is the name of a built-in function of Python, even if it has not caused any trouble (yet) in your case
You can use the sum built-in function to sum the elements of a list
The else after the while is not useful
You can do a = sum([a,b]) to assign directly a without using a temporary variable c.

Finally here is my suggestion of code:

a = int(input("what is the number you want to add?: "))

ask = "yes"
while (ask == "yes"):
    b = int(input("what is the number you want to add?: "))
    a = sum([a,b])
    ask = input("do you want to add another number?: ")

print (a)

edited Apr 26 '18 at 15:24

answered Apr 26 '18 at 12:56

Laurent H.

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`sum` is NOT a "reserved built-in symbol", it's just a builtin function. If it was a reserved name, trying to use it as an identifier would raise a SyntaxError. – bruno desthuilliers Apr 26 '18 at 13:04
@brunodesthuilliers You're right, sir ! I have updated my answer. Thanks a lot. – Laurent H. Apr 26 '18 at 15:24

Function to sum multiple numbers

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