TypeError: unsupported operand type(s) for -: 'float' and 'NoneType' python

Question

Does anyone know why I would be getting an error like this?! I would really appreciate it if you do, I am new to this and trying to learn but im getting really caught up in the nitty gritty of python! this is the error I am getting:

eError: unsupported operand type(s) for -: 'float' and 'NoneType'

 for test in test_set:
 person_id = test['person_id']
 place_id = test['place_id']
 rating = test['rating']
 predicted_rating = simple_nn(person_id, place_id, 5)
 #difference =  (rating- predicted_rating)
 sq_err = (rating- predicted_rating) * (rating - predicted_rating)

 sq_err_sum = sq_err 

 sq_err_sum = sq_err_sum + sq_err



 rmse = math.sqrt(sq_err_sum/5)
 print rmse

Answer 1

In my case, I forgot to add

return

to the computed expression in the function definition.

Example:

def drift(y, t): theta*(mu-y)  # define OUP drift term
def diffusion(y, t): sigma  # define OUP diffusion term

will return the type 'None' when called,

where as,

def drift(y, t): return theta*(mu-y)  # define OUP drift term
def diffusion(y, t): return sigma  # define OUP diffusion term

will return actual numbers

Answer 2

Judging by what you've provided, and the error this is my conclusion.

The only place you use the - operand is in the two points

sq_err = (rating- predicted_rating) * (rating - predicted_rating)

because the error states 'float' and 'NoneType' we can conclude that rating is type float and predicted_rating is NoneType.

You defined predicted_rating as:

predicted_rating = simple_nn(person_id, place_id, 5)

So this means that somewhere in your code for the function simple_nn you are not returning anything. Perhaps if you used conditions you didn't evaluate every end path and the function simply returned.

for example... all of these functions return the None type.

def example1():
    pass

def example2():
    return

def example3(a = True, b  = True):
    if not a:
        return True
    elif not b:
        return False

Note in the last example there is a path where neither if case is satisfied,.. thus it could return None