Special Attributes¶

This document covers some of the special attributes used by this module.

When we discuss interfaces or the contents of attributes, we are referring to tagged values. Unless otherwise noted, tagged values must be set directly on the object in question; they are not inherited from parent objects.

__external_class_name__

Used an a class or interface to determine the value of the Class standard external value. Usually this is a string, but when using InterfaceObjectIO (including ext:registerAutoPackageIO) it can be a callable returning a string or None

This value is inherited; the first non-None value in the resolution order will be used (the distinction matters when using callables).

__external_can_create__

This boolean value is set to true on factory functions (e.g., classes). ext:registerAutoPackageIO sets it to true automatically.

mimeType

Part of the zope.mimetype.interfaces.IContentTypeAware interface. This is read from Factories when creating factory registrations. It also forms one of the standard external fields.

_ext_excluded_out

A tagged value on individual attributes of an interface to prevent them from being externalized. See InterfaceObjectIO.

__external_factory_wants_arg__

(Provisional). Attribute of a factory. When creating sub-objects and invoking a factory, should we pass the external object to the factory? If not true or not set, the factory receives no arguments.

New in version 1.0a3.

__external_default_implementation__

(Provisional). Tagged value of an interface implemented by one of the factories discovered by ext:registerAutoPackageIO holding the primary factory discovered for that interface. Used when internalizing anonymous external data.

This value is inherited.

New in version 1.0a8.

__external_accept_id__

For attributes. Documentation needed.

_ext_is_marker_interface

When searching for a schema to use for externalization, interfaces with this tagged value directly set will not be considered.