Is there a better way to produce a delta value in Python?

Hi fellow stackoverflow'ers,

I'm pretty good with Python but I'm trying to see if there is a better way to do the following. I need to produce a delta to adjust stock levels. I have the following code which works, but could it be done faster/more Pythonic?

a = 100
b = 50

def negativeNumber(x): # From https://stackoverflow.com/a/64445338/22669764
    neg = x * (-1)
    return neg

if not a == b: 
    if b < a:
        delta_qty = negativeNumber(a - b)
    if b > a:
        delta_qty = b - a
    if b == 0:
        delta_qty = negativeNumber(a)
if a == 0 and b == 0:
    delta_qty = 0

The above works and produce the following results:

b<a = -50
b>a = 50 (If we swapped the values)
b=0 = -100 (If b=0)
a=0 & b=0 = 0 (I need this to set a variable not shown in example)

Is there is a faster/tidier/more Pythonic way I would achieve the same results?

EDIT: Thanks for the answers and comments, Goku's answer and Homer512 comment look to achieve what I need in a far neater fashion.

If you want negative sign (as you have shown in example) in your result then:

def your_func(a,b):
    return b-a                   # it will give negative when a > b and vice-versa

If you do not want negative sign no matter which is bigger a or b then :

def your_func(a,b):
    return abs(b-a)

delta_qty = your_func(a,b)