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""" A hook to allow code be executed when a class is loaded. """
# Standard library imports.
import sys
# Enthought library imports.
from enthought.traits.api import Callable, HasTraits, MetaHasTraits, Str
class ClassLoadHook(HasTraits):
""" A hook to allow code to be executed when a class is loaded.
If the class is *already* loaded when the 'connect' method is called then
the code is executed immediately.
"""
#### 'ClassLoadHook' interface ############################################
# The name of the class. When this class is loaded the 'on_class_loaded'
# method is called.
class_name = Str
# A callable that will be executed when the class is loaded. The callable
# must take a single argument which will be the loaded class.
#
# This is used in the default implementation of 'on_class_loaded'. If you
# override that, then you don't have to set to this trait.
on_load = Callable
###########################################################################
# 'ClassLoadHook' interface.
###########################################################################
def connect(self):
""" Connect the load hook to listen for the class being loaded. """
MetaHasTraits.add_listener(self.on_class_loaded, self.class_name)
# If the class has already been loaded then run the code now!
cls = self._get_class(self.class_name)
if cls is not None:
self.on_class_loaded(cls)
return
def disconnect(self):
""" Disconnect the load hook. """
MetaHasTraits.remove_listener(self.on_class_loaded, self.class_name)
return
def on_class_loaded(self, cls):
""" This method is called when the class is loaded.
If 'self.on_load' is not None, it calls 'self.on_load(cls)'.
"""
if self.on_load is not None:
self.on_load(cls)
return
###########################################################################
# Private interface.
###########################################################################
def _get_class(self, class_path):
""" Returns the class defined by *class_path*.
Returns **None** if the class has not yet been loaded.
"""
# Only check if the class name has at least a partial hierarchy.
#
# fixme: Comment should say why!
if '.' in class_path:
components = class_path.split('.')
module_name = '.'.join(components[:-1])
class_name = components[-1]
# The class is loaded if its module has been imported and the class
# is defined in the module dictionary.
module = sys.modules.get(module_name, None)
if module is not None and hasattr(module, class_name):
klass = getattr(module, class_name)
else:
klass = None
else:
klass = None
return klass
#### EOF ######################################################################
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