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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_pixels(self, pix, depth):
 """ Add one or more HEALPix pixels to this region. Parameters pix : int or iterable The pixels to be added depth : int The depth at which the pixels are added. """

        if depth not in self.pixeldict:
            self.pixeldict[depth] = set()
        self.pixeldict[depth].update(set(pix))