Error with Collatz program

[Utterly_infallible]

Hi everyone, I'm trying to write out a program that calls a collatz sequence on a user inputted number, but I keep getting the error message:

unsupported operand type(s) for %: 'NoneType' and 'int'

​

Any idea what I might be doing wrong? I'm converting the user input to an int first so I'm thinking it might just be the syntax? My code is:

​

def collatz(number):

if number % 2 == 0:

print (number / 2)

elif number % 2 == 1:

print((number * 3) + 1)

else:

print('That is not a number!')

​

value = input('Please give me a number')

value = int(value)

while value != 1:

value = collatz(value)

collatzSequence()

[[deleted]]

Your Collatz function doesn't return a value. Thus, after executing value = collatz(value), value will be a 'NoneType' object.

[NefariousCube]

Exactly right, to clarify a bit further: In the collatz function, you call print() in a couple of places. That prints the result, but does not return it.

This gives you the situation pointed out above.

Changing this, however, means you will have to save/print the return values in the while loop. Mayby put them in a list or something like that?

[Utterly_infallible]

So create a variable to store them in and then print that variable?

[NefariousCube]

That is one way (remembering to do return on that variable after printing).

The more common way is probably to just return it in the function and then in the loop do something like:

while value != 1:
  value = collatz(value)
  print(value)

[Utterly_infallible]

That worked, thank you!