Guys can someone help me to understand why doesn't my python decorator work properly?

created a decorator that would print the below mentioned text after returning the count of car\_fuel() function. 

```
def decor(func):
    def wrapper(a):
        func(a)
        print('Bring 10 coupons and get a gallon of fuel for free')
    return wrapper

@decor
def car_fuel(a):
    b={'petrol':3.6,'diesel':3} #types of fuel and prices
    count = 0
    for i in a.keys():
        if i in b.keys():
            count+= a[i]*b[i]
    return count

abc={'petrol':10} # the fuel that i wanna buy and gallons
print(car_fuel(abc))

```

I want to have the following result: 

> 
> 36 
>  Bring 10 coupons and get a gallon of fuel for free 
> 
> 
> 

but what I get is:

> 
> Bring 10 coupons and get a gallon of fuel for free
>  None
> 
> 
> 

Why don't I receive 36 before the "Bring 10 coupons...." sentence and why does it return None?