python - TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

Question

I am new to Python and I'm sure that I'm doing something wrong - I would like to ask a user for three numbers and print their sum, here's my current code:

for i in range(0, 3):
    total = None
    num = input('Please enter number {}:'.format(str(i)))
    total += num

By the way, the total = None was to try and declare the variable so I could use it without setting a value? I get this

Traceback (most recent call last):
  File "<pyshell#20>", line 4, in <module>
    total += num
TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

Answer 1

You shouldn't do total = None. NoneType cannot be used against addition.

There's an extra problem suggested by the error message: From your description you're trying to add 3 numbers, but the return type of the builtin input() is str. So this is what you're supposed to write:

total = 0
for i in range(0, 3):
    num = input('Please enter number {}:'.format(str(i)))
    total += int(num)

All the points:

• Indent the code correctly. Indentation is a crucial part of Python.
• Don't set total to zero at every loop. Only set it once outside the loop
• Take care of types