[python] Python Error: unsupported operand type(s) for +: 'int' and 'NoneType'

I don't understand this error OR what it means. I will paste my code underneath, but I don't think it is really relevant; I just want to understand this error.

It's just a bit of code to add up the letters in all numbers 1 - 1000 (inclusive)

def number_translator(x):
    if x == 1:
        return 3
    elif x == 2:
        return 3
    elif x == 3:
        return 5
    elif x == 4:
        return 4
    elif x == 5:
        return 4
    elif x == 6:
        return 3
    elif x == 7:
        return 5
    elif x == 8:
        return 5
    elif x == 9:
        return 4
    elif x == 10:
        return 3
    elif x == 11:
        return 6
    elif x == 12:
        return 6
    elif x == 14:
        return 8
    elif x == 15:
        return 7
    elif x == 16:
        return 7
    elif x == 17:
        return 9
    elif x == 18:
        return 8
    elif x == 19:
        return 8
    elif x == 20:
        return 6
    elif x == 30:
        return 6
    elif x == 40:
        return 5
    elif x == 50:
        return 5
    elif x == 60:
        return 5
    elif x == 70:
        return 7
    elif x == 80:
        return 6
    elif x == 90:
        return 6

count = 0
for element in range(1, 1001):
    if element < 21:
        count += number_translator(element)              # for numbers 1 - 20
    elif 20 < element < 100:
        count += number_translator(int(str(element)[0]) * 10) + number_translator(int(str(element)[1]))  # for numbers 21 through 100
    elif element % 100 == 0 and element != 1000:
        count += number_translator(int(str(element)[0])) + 7   # for numbers divisible by 100, but not 1000
    elif element == 1000:
        count += 11                                          # just for 1000
    elif element % 100 < 20:
        count += number_translator(int(str(element)[0])) + 10 + number_translator(int(str(element)[1:3]))      # now I add in numbers like 101 - 120, 201 - 220, etc.
    else:
        count += number_translator(int(str(element)[0])) + 10 + number_translator(int(str(element)[1]) * 10) + number_translator(int(str(element)[2])) # now the rest( 121, 122, 123, 225, 256, 984, etc.)

print(count)

I got a similar error with '/' operand while processing images. I discovered the folder included a text file created by the 'XnView' image viewer. So, this kind of error occurs when some object is not the kind of object expected.

In your giant elif chain, you skipped 13. You might want to throw an error if you hit the end of the chain without returning anything, to catch numbers you missed and incorrect calls of the function:

...
elif x == 90:
    return 6
else:
    raise ValueError(x)