<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _generate_docstring_for_func(self, namespace, arg_data_type, result_data_type=None, error_data_type=None, overview=None, extra_request_args=None, extra_return_arg=None, footer=None):
 """ Generates a docstring for a function or method. This function is versatile. It will create a docstring using all the data that is provided. :param arg_data_type: The data type describing the argument to the route. The data type should be a struct, and each field will be treated as an input parameter of the method. :param result_data_type: The data type of the route result. :param error_data_type: The data type of the route result in the case of an error. :param str overview: A description of the route that will be located at the top of the docstring. Describes any additional parameters for the method that aren't a field in arg_data_type. :param str extra_return_arg: Name of an additional return type that. If this is specified, it is assumed that the return of the function will be a tuple of return_data_type and extra_return-arg. :param str footer: Additional notes at the end of the docstring. """

        fields = [] if is_void_type(arg_data_type) else arg_data_type.fields
        if not fields and not overview:
            # If we don't have an overview or any input parameters, we skip the
            # docstring altogether.
            return

        self.emit('"""')
        if overview:
            self.emit_wrapped_text(overview)

        # Description of all input parameters
        if extra_request_args or fields:
            if overview:
                # Add a blank line if we had an overview
                self.emit()

            if extra_request_args:
                for name, data_type_name, doc in extra_request_args:
                    if data_type_name:
                        field_doc = ':param {} {}: {}'.format(data_type_name,
                                                              name, doc)
                        self.emit_wrapped_text(field_doc,
                                               subsequent_prefix='    ')
                    else:
                        self.emit_wrapped_text(
                            ':param {}: {}'.format(name, doc),
                            subsequent_prefix='    ')

            if is_struct_type(arg_data_type):
                for field in fields:
                    if field.doc:
                        if is_user_defined_type(field.data_type):
                            field_doc = ':param {}: {}'.format(
                                field.name, self.process_doc(field.doc, self._docf))
                        else:
                            field_doc = ':param {} {}: {}'.format(
                                self._format_type_in_doc(namespace, field.data_type),
                                field.name,
                                self.process_doc(field.doc, self._docf),
                            )
                        self.emit_wrapped_text(
                            field_doc, subsequent_prefix='    ')
                        if is_user_defined_type(field.data_type):
                            # It's clearer to declare the type of a composite on
                            # a separate line since it references a class in
                            # another module
                            self.emit(':type {}: {}'.format(
                                field.name,
                                self._format_type_in_doc(namespace, field.data_type),
                            ))
                    else:
                        # If the field has no docstring, then just document its
                        # type.
                        field_doc = ':type {}: {}'.format(
                            field.name,
                            self._format_type_in_doc(namespace, field.data_type),
                        )
                        self.emit_wrapped_text(field_doc)

            elif is_union_type(arg_data_type):
                if arg_data_type.doc:
                    self.emit_wrapped_text(':param arg: {}'.format(
                        self.process_doc(arg_data_type.doc, self._docf)),
                        subsequent_prefix='    ')
                self.emit(':type arg: {}'.format(
                    self._format_type_in_doc(namespace, arg_data_type)))

        if overview and not (extra_request_args or fields):
            # Only output an empty line if we had an overview and haven't
            # started a section on declaring types.
            self.emit()

        if extra_return_arg:
            # Special case where the function returns a tuple. The first
            # element is the JSON response. The second element is the
            # the extra_return_arg param.
            args = []
            if is_void_type(result_data_type):
                args.append('None')
            else:
                rtype = self._format_type_in_doc(namespace,
                                                 result_data_type)
                args.append(rtype)
            args.append(extra_return_arg)
            self.generate_multiline_list(args, ':rtype: ')
        else:
            if is_void_type(result_data_type):
                self.emit(':rtype: None')
            else:
                rtype = self._format_type_in_doc(namespace, result_data_type)
                self.emit(':rtype: {}'.format(rtype))

        if not is_void_type(error_data_type) and error_data_type.fields:
            self.emit(':raises: :class:`{}`'.format(self.args.error_class_path))
            self.emit()
            # To provide more clarity to a dev who reads the docstring, suggest
            # the route's error class. This is confusing, however, because we
            # don't know where the error object that's raised will store
            # the more detailed route error defined in stone.
            error_class_name = self.args.error_class_path.rsplit('.', 1)[-1]
            self.emit('If this raises, {} will contain:'.format(error_class_name))
            with self.indent():
                self.emit(self._format_type_in_doc(namespace, error_data_type))

        if footer:
            self.emit()
            self.emit_wrapped_text(footer)
        self.emit('"""')