#------------------------------------------------------------------------------
# Copyright (c) 2012, Enthought, Inc.
# All rights reserved.
#------------------------------------------------------------------------------
from abc import ABCMeta, abstractmethod
[docs]class AbstractExpression(object):
""" An abstract interface definition for creating expressions.
Expressions are registered with `Declarative` instances using the
`bind_expression` method to provide computed attribute values.
"""
__metaclass__ = ABCMeta
@abstractmethod
[docs] def eval(self, obj, name):
""" Evaluate and return the results of the expression.
Parameters
----------
obj : Declarative
The declarative object which owns the expression.
name : str
The attribute name on `obj` for which this expression is
providing the value.
"""
raise NotImplementedError
[docs]class AbstractListener(object):
""" An interface definition for creating attribute listeners.
Listeners are registered with `Declarative` instances using the
`bind_listener` method to track changes to their attributes.
"""
__metaclass__ = ABCMeta
@abstractmethod
[docs] def value_changed(self, obj, name, old, new):
""" Called when the attribute on the object has changed.
Parameters
----------
obj : Declarative
The Declarative object which owns the attribute.
name : str
The name of the attribute which changed.
old : object
The old value of the attribute.
new : object
The new value of the attribute.
"""
raise NotImplementedError