# Format unmarshallers

Based on `format` keyword, openapi-core can also unmarshal values to specific formats.

Openapi-core comes with a set of built-in format unmarshallers, but it’s also possible to add custom ones.

Here’s an example with the `usdate` format that converts a value to date object:

      from datetime import datetime

      def unmarshal_usdate(value):
         return datetime.strptime(value, "%m/%d/%y").date

      extra_format_unmarshallers = {
         'usdate': unmarshal_usdate,
      }

      config = Config(
         extra_format_unmarshallers=extra_format_unmarshallers,
      )
      openapi = OpenAPI.from_file_path('openapi.json', config=config)

      result = openapi.unmarshal_response(request, response)