Running total with arguments - python

Question

I'm trying to make a simple adding function here. I start a count at 0. I want to add the argument of add_credits(x) to the credit total, to keep a running total. A for loop doesn't seem like the right thing to use here, since I don't know how many times I'll be looping.

So what I want to do here is, add 3. Credits = 3. Add 4, credits = 7.

credits = 0
def add_credits(x):
    new_total = credits + x
    return new_total

print (add_credits(3))
print (add_credits(4))

I know the solution must be really simple... I feel like an idiot.

Functions aren't meant to be used like this. You'd be better served by making a class instead. — Ignacio Vazquez-Abrams
– Ignacio Vazquez-Abrams, Commented Feb 17, 2018 at 22:17
@IgnacioVazquez-Abrams why are functions not meant to be used like this? — Erich Purpur
– Erich Purpur, Commented Feb 18, 2018 at 0:47
They are meant to optionally accept arguments and return a result, without side effects. There are other constructs that can be used if side effects are required. — Ignacio Vazquez-Abrams
– Ignacio Vazquez-Abrams, Commented Feb 18, 2018 at 0:49

Evya · Accepted Answer · 2018-02-17 22:20:23Z

3

You can use a class to represent some sort of "Wallet" object. This will hold an attribute of total and an add function:

class Wallet:
    def __init__(self):
        self.total = 0

    def add_to_total(self, amount):
        self.total += amount


wallet = Wallet()
wallet.add_to_total(5)
print(wallet.total) # outputs 5

answered Feb 17, 2018 at 22:20

Evya

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Joshua Yonathan · Accepted Answer · 2018-02-17 22:24:57Z

1

in your example, the credits variable in the function is a local variable. This means it does not share the same value you assigned it at the top. You need to identify it as global for it to work like this:

credits = 0
def add_credits(x):
    global credits
    credits = credits + x
    return credits 

print (add_credits(3))
print (add_credits(4))

answered Feb 17, 2018 at 22:24

Joshua Yonathan

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Bennett Brown · Accepted Answer · 2018-02-17 22:23:11Z

0

Code within a function will not change the value of a variable passed to it when the variable represents an int.

answered Feb 17, 2018 at 22:23

Bennett Brown

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Jeremiah · Accepted Answer · 2018-02-17 22:23:47Z

0

If you really want to increment the credits variable within the function, you can use global:

credits = 0


def add_credits(x):
    global credits
    credits += x


add_credits(3)
print(credits) # 3

add_credits(4)
print(credits) # 7

But using global in this way is not recommended, so I would definitely use Evyatar's solution.

answered Feb 17, 2018 at 22:23

Jeremiah

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