How do you call update with a new_value of 20?

Can someone please explain how to call the function?

When I try it does not output, says none

def update(new_value = 10):
  old_value = new_value

print(update(20))

In Python, a function that does not have an explicit return statement returns the value None.

print() is such a function. print() evaluates the expression within its parentheses, takes the returned value and sends a string representation of that value to the i/o device (usually, your screen), and returns None.

so then technically, the function as written will not generate an output because its missing “return”?

Correct. You need an explicit return statement.

def update(new_value = 10):
    old_value = new_value
    return old_value

print(update(20))