I’ve got an object that is basically an int with some extra properties. Can I coerce it into an int when it’s used as a list index?

Context: I’m making a game that happens in a maze made of square tiles and almost everything, from movement to attacks, involves directions, which are mostly used to index lists. Subtracting or adding to directions is an easy way to turn left or right, but I always have to check that they are still within bounds, and I would like to automate that by making a custom class.

Here is how I’m currently doing it:

global UP
UP = 0
global RIGHT
RIGHT = 1
global DOWN
DOWN = 2
global LEFT
LEFT = 3

And here is what I’d like to do:

class Direction:
    number_of_directions=4

    def __init__(self,direction):
        self.direction = direction

    def __int__(self):
        return self.direction

    def __add__(self,other): #Here other is supposed to be an int
        return (self.direction + other)%number_of_directions

    def __sub__(self,other): #Here other is supposed to be an int
        return (self.direction - other)%number_of_directions

global UP
UP = Direction(0)
global LEFT
LEFT = Direction(1)
global DOWN
DOWN = Direction(2)
global RIGHT
RIGHT = Direction(3)

The only problem with that is that I am using UP, RIGHT, etc. as indexes, like I have a Tile that has a list of four Wall and I constantly call Tile.walls[direction] with direction being one of my four constants, and I don’t want to have to specify Tile.walls[int(direction)] everytime.

Is there a way to have direction automatically coerced into an int whenever it’s used for indexing?

Answer

Yes, simply define __index__(). For example:

class Direction:

    def __init__(self, direction):
        self.direction = direction

    def __index__(self):
        return self.direction

UP = Direction(0)
cardinals = ['north', 'east', 'south', 'west']
print(cardinals[UP])  # -> north

This also makes __int__ unnecessary since __index__ is used as a fallback.

print(int(UP))  # -> 0

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P.S. For this answer, I’m ignoring any design considerations. Using an IntEnum might be a better solution, I’m not sure.