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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def check_initialized(self):
 """Check class for initialization status. Check that all required fields are initialized Raises: ValidationError: If message is not initialized. """

        for name, field in self.__by_name.items():
            value = getattr(self, name)
            if value is None:
                if field.required:
                    raise ValidationError(
                        "Message %s is missing required field %s" %
                        (type(self).__name__, name))
            else:
                try:
                    if (isinstance(field, MessageField) and
                            issubclass(field.message_type, Message)):
                        if field.repeated:
                            for item in value:
                                item_message_value = field.value_to_message(
                                    item)
                                item_message_value.check_initialized()
                        else:
                            message_value = field.value_to_message(value)
                            message_value.check_initialized()
                except ValidationError as err:
                    if not hasattr(err, 'message_name'):
                        err.message_name = type(self).__name__
                    raise