Retrieves calendar class associated with given ``iso_code``.

        If calendar of subdivision is not registered
        (for subdivision like ISO codes, e.g. GB-ENG)
        returns calendar of containing region
        (e.g. United Kingdom for ISO code GB) if it's available.

        :rtype: Calendar

def get_calendar_class(self, iso_code):
        """
        Retrieves calendar class associated with given ``iso_code``.

        If calendar of subdivision is not registered
        (for subdivision like ISO codes, e.g. GB-ENG)
        returns calendar of containing region
        (e.g. United Kingdom for ISO code GB) if it's available.

        :rtype: Calendar
        """
        code_elements, is_subregion = self._code_elements(iso_code)
        if is_subregion and iso_code not in self.region_registry:
            # subregion code not in region_registry
            code = code_elements[0]
        else:
            # subregion code in region_registry or is not a subregion
            code = iso_code
        return self.region_registry.get(code)