def validate(self, reason=True):
        # type: (bool) -> list
        """Return the validation results and include an (optional) reason.

        If reason keyword is true, the validation is returned for each validation
        the [(<result: bool>, <reason:str>), ...]. If reason is False, only a single list of validation results
        for each configured validator is returned.

        :param reason: (optional) switch to indicate if the reason of the validation should be provided
        :type reason: bool
        :return: list of validation results [bool, bool, ...] or
                 a list of validation results, reasons [(bool, str), ...]
        :rtype: list(bool) or list((bool, str))
        :raises Exception: for incorrect validators or incompatible values
        """
        self._validation_results = [validator.is_valid(self._value) for validator in getattr(self, '_validators')]
        self._validation_reasons = [validator.get_reason() for validator in getattr(self, '_validators')]

        if reason:
            return list(zip(self._validation_results, self._validation_reasons))
        else:
            return self._validation_results