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Python Object-Oriented Python Advanced Objects Math

Not getting the __radd__ part of the code

For the __add__ method, he uses the if statement to test for float or int properties, why doesn't he need to do it again for the __radd__? I'm not getting the explanation from the video. :\

1 Answer

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

He avoids retesting for floats/ints in __radd__ by passing the problem on to __add__. All __radd__ has to do is receive and pass along the arguments.

Post back if you need more help. Good luck!!!

Are you saying all the __radd__ does is catch the reflected add call, while the return self + other portion of the __radd__ passes argument directly to the __add__ method?

... or is he saying that the return self + other passes the argument back to NumString(2) + 2 at which point, the __add___ method is called?

and when he says this isn't always the case... would the following be an example, where ... let's say you want to return a single title cased string whenever adding the ProperStrings class:

class ProperStrings:
    def __init__(self, value):
        self.value = str(value)
    def __add__(self, other):
        return self.value.title() + other.lower()
    def __radd__(self, other):
        return other.title() + self.value.lower()

where it's not always the case that __radd__ returns self + other?

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

Are you saying all the radd does is catch the reflected add call, while the return self + other portion of the radd passes argument directly to the add method? Yes, exactly.

Normally, the __radd__ would return self + other so that the "self" is now on the left-side of the plus sign. This would then automatically trigger __add__ since we are now adding "self" again.

In your ProperStrings class, the behavior is slightly different. Since the __radd__ is returning a .title() + .title(), these both result in strings so the plus sign going to cause calling the string __add__ method. It only stays in this class's methods if one of the operands is "self".

Oh okay, I get it now. Thanks, Chris!

I guess for my ProperStrings example, I was trying to give an example of Kenneth's comment that return self + other might not be appropriate for every __radd__ method. Here what I meant to type was that since ProperStrings returns a title cased concatenated string every time, the __radd__ wouldn't work with simply return self + other

:D I get it now though. dang I can't wait to play around with it. I'm sure this is only the basic of the basics... :'(