code: def assign(self, link_type, product, linked_product, data=None,
                 identifierType=None):
          
          return bool(self.call('catalog_product_link.assign',
                  [link_type, product, linked_product, data, identifierType]))
docs: Assign a product link
  
          :param link_type: type of link, one of 'cross_sell', 'up_sell',
                  'related' or 'grouped'
          :param product: ID or SKU of product
          :param linked_product: ID or SKU of linked product
          :param data: dictionary of link data, (position, qty, etc.)
                  Example: { 'position': '0', 'qty': 1}
          :param identifierType: Defines whether the product or SKU value is
                                 passed in the "product" parameter.
  
          :return: boolean