Definition of an interface is quite trivial. An example from cubicweb

itself (found in cubicweb/interfaces.py):

.. sourcecode:: python

    class ITree(Interface):

        def parent(self):

            """returns the parent entity"""

        def children(self):

            """returns the item's children"""

        def children_rql(self):

            """XXX returns RQL to get children"""

        def iterchildren(self):

            """iterates over the item's children"""

        def is_leaf(self):

            """returns true if this node as no child"""

        def is_root(self):

            """returns true if this node has no parent"""

        def root(self):

            """returns the root object"""

.. sourcecode:: python

  from cubicweb.interfaces import ITree

  from cubicweb.mixins import TreeMixIn

  class MyEntity(TreeMixIn, AnyEntity):

      __regid__ = 'MyEntity'

      __implements__ = AnyEntity.__implements__ + ('ITree',)

      tree_attribute = 'filed_under'

The TreeMixIn here provides a default implementation for the

interface. The tree_attribute class attribute is actually used by this

implementation to help implement correct behaviour.

Interfaces (and some implementations as mixins) defined in the library

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. automodule:: cubicweb.mixins

   :members: