Python Kivy: Rescale an image to fit a given viewport size without losing aspect ratio

gistfile1.py

class MyImage(Image):
    def __init__(self, **kwargs):
        super(MyImage, self).__init__()

    def texture_width(self):
        return self.texture.size[0]

    def texture_height(self):
        return self.texture.size[1]

    def rescale(self, width, height):
        """
        Resize the image to fit the given dimensions, zooming in or out if
        needed without losing the aspect ratio
        :param width: target width
        :param height: target height
        :return: new dimensions as a tuple (width, height)
        """
        ratio = 0.0
        new_width = 0.0
        new_height = 0.0

        target_width = float(width)
        target_height = float(height)

        image_width = float(self.texture_width())
        image_height = float(self.texture_height())

        ratio = target_width / image_width
        new_width = image_width * ratio
        new_height = image_height * ratio

        if (new_height < target_height):
            ratio = target_height / new_height
            new_height *= ratio
            new_width *= ratio

        if new_width > 0 and new_height > 0:
            self.width = new_width
            self.height = new_height

        return (new_width, new_height)