code: def add_photo(self, collection_id, photo_id):
          
          url = "/collections/%s/add" % collection_id
          data = {
              "collection_id": collection_id,
              "photo_id": photo_id
          }
          result = self._post(url, data=data) or {}
          return CollectionModel.parse(result.get("collection")), PhotoModel.parse(result.get("photo"))
docs: Add a photo to one of the logged-in user’s collections.
          Requires the 'write_collections' scope.
  
          Note: If the photo is already in the collection, this acion has no effect.
  
          :param collection_id [string]: The collection’s ID. Required.
          :param photo_id [string]: The photo’s ID. Required.
          :return: [Tuple]: The Unsplash Collection and Photo