code: def _product_file_hash(self, product=None):
          
          if self.hasher is None:
              return None
          else:
              products = self._rectify_products(product)
              product_file_hash = [
                  util_hash.hash_file(p, hasher=self.hasher, base='hex')
                  for p in products
              ]
              return product_file_hash
docs: Get the hash of the each product file