code: def image_url(self, pixel_size=None):
          
          if "profile" not in self._raw:
              return
          profile = self._raw["profile"]
          if (pixel_size):
              img_key = "image_%s" % pixel_size
              if img_key in profile:
                  return profile[img_key]
          return profile[self._DEFAULT_IMAGE_KEY]
docs: Get the URL for the user icon in the desired pixel size, if it exists. If no
          size is supplied, give the URL for the full-size image.