Improved DateField.to_python() to catch invalid dates like Feb. 31

        if isinstance(value, datetime.date):

            return value

        validators.isValidANSIDate(value, None)

        try:

            return datetime.date(*time.strptime(value, '%Y-%m-%d')[:3])

        except ValueError:

            raise validators.ValidationError, gettext('Enter a valid date in YYYY-MM-DD format.')

    def get_db_prep_lookup(self, lookup_type, value):

        if lookup_type == 'range':