Python: How do I convert a NonType variable to a String?

Question

I have the following function:

>>> def rule(x):
... rule = bin(x)[2:].zfill(8)
... rule = str(rule)
... print rule

I am trying to convert rule into a string, but when I run the following command, here is what I get:

>>> type(rule(20))
00010100
<type 'NoneType'>

What is a NoneType variable and how can I convert this variable into a string?

Thanks,

Answer 1

you need to do:

def rule(x):
 return bin(x)[2:].zfill(8)

All functions return None implicitly if no return statement was encountered during execution of the function (as it is in your case).

Answer 2

Your rule function doesn't return anything -- it only prints. So, rule(20) returns None -- the python object representing 'no value'. You can't turn that into a string, at least not in the way you are expecting.

You need to define rule to return something, like this:

>>> def rule(x):
... rule=bin(x)[2:].zfill(8)
... rule=str(rule)
... return rule

Then it will return a string object.