When to decide whether or not to have an argument in a class method?

[buran]

to the particular error in your code (the first one) you should amend the code as follows
 

    def price(self, otherSide):
        if otherSide**3 < self.volume():
            return "The house is more expensive" 
 

however there are many flaws in your code. some of them:
- first of all price method will return None if the volume of other house has bigger/same volume
- method name (price) is misleading. one would expect it to return/calculate price. more appropriate name should be used
- it's more logical to take as argument another house object, not side size