TypeError: '>' not supported between instances of 'NoneType' and 'int'

Question

I'm trying to have written this code with the decorator that has to show these multiples (which are of 3 and 5) and their sum by typing a number of maximum range.

Here is it:
def multi(max_case):
def three_and_five():
n = max_case()
sum = 0
while n > 1:
if n%3==0 or n%5==0:
sum+=n
print(n)
elif n%3==0 and n%5==0:
sum+=n
print(n)
n-=1
print('\n'+str(sum))
return three_and_five
@multi
def add_value():
n = int(input('Type a natural number: '))
print(n)
add_value()

Unfortunately there must be something wrong, because after running that and entering integer value I got this output:
Line 5: TypeError: '>' not supported between instances of 'NoneType' and 'int'

Does anyone have an idea why it's so and how to solve it?

Answer 1

Nicole Shevrill
add_value is a void function that returns None.

In the decorator you use
n=max_case()
when you run add_value, this becomes
n = add_value()
but add_value does not have a return
statement, so it returns None.
so:
n = None
You can't use this for your conditional statements.
The decorator ends up comparing None to int.

add a return n to your add_value function.

Answer 2

Nicole Shevrill
This second example does not depend on the return value of the decorated function.
You can pass it an empty function and it will still work.

@decor
def print_text():
pass

print_text()

Answer 3

Thanks! Now it really works, but there is another thing that made me curious:

def decor(put_it_here):
def wrap():
print("============")
w = put_it_here()
print("============")
return wrap
@decor
def print_text():
w = input()
print(w)
print_text()

Why was return not needed as in the example above?

Answer 4

Thank you for your help, now it seems understandable to me.