Merge pull request #209 from enthought/code-tracing

Code tracing

.gitignore

@@ -3,6 +3,7 @@
 *.swp
 *.egg-info
 *.so
+*.pyd
 *.DS_Store
 *.enamlc
 *.c

enaml/__init__.py

@@ -6,11 +6,11 @@
 #------------------------------------------------------------------------------
 # Logging Setup
 #------------------------------------------------------------------------------
-# Add a NullHandler to make sure that all enaml loggers don't complain when they
-# get used.
+# Add a NullHandler so enaml loggers don't complain when they get used.
 import logging
 
 class NullHandler(logging.Handler):
+
     def handle(self, record):
         pass
 
@@ -33,14 +33,14 @@ def imports():
     """ Lazily imports and returns an enaml imports context.
 
     """
-    from .core.import_hooks import imports
+    from enaml.core.import_hooks import imports
     return imports()
 
 
 #------------------------------------------------------------------------------
 # Operator Context Functions
 #------------------------------------------------------------------------------
-#: The private storage for the optional default operator context function 
+#: The private storage for the optional default operator context function
 #: which overrides that which is provided by default.
 _default_operator_context_func = None
 
@@ -53,7 +53,7 @@ def set_default_operator_context_func(func):
     func : callable
         A callable object which takes no arguments and returns an
         instance of OperatorContext.
-    
+
     """
     global _default_operator_context_func
     _default_operator_context_func = func

enaml/core/abstract_expressions.py

@@ -0,0 +1,80 @@
+#------------------------------------------------------------------------------
+#  Copyright (c) 2012, Enthought, Inc.
+#  All rights reserved.
+#------------------------------------------------------------------------------
+from abc import ABCMeta, abstractmethod
+
+from enaml.signaling import Signal
+
+
+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
+    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
+
+
+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
+    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
+
+
+class AbstractListenableExpression(AbstractExpression):
+    """ An abstract interface definition for creating listenable
+    expressions.
+
+    Listenable expressions are registered with `Declarative` instances
+    using the `bind_expression` method to provide dynamically computed
+    attribute values at runtime.
+
+    """
+    #: An Enaml Signal emitted by the expression when it becomes invalid.
+    #: The payload of the signal will be the name that was passed to the
+    #: `eval` method during the last expression evaluation.
+    invalidated = Signal()
+