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""" An object that can be initialized from a preferences node. """
# Standard library imports.
import logging
# Enthought library imports.
from traits.api import HasTraits, Instance, Str, Unicode
# Local imports.
from .i_preferences import IPreferences
from .package_globals import get_default_preferences
# Logging.
logger = logging.getLogger(__name__)
class PreferencesHelper(HasTraits):
""" An object that can be initialized from a preferences node. """
#### 'PreferencesHelper' interface ########################################
# The preferences node used by the helper. If this trait is not set then
# the package-global default preferences node is used.
#
# fixme: This introduces a 'sneaky' global reference to the preferences
# node!
preferences = Instance(IPreferences)
# The path to the preference node that contains the preferences that we
# use to initialize instances of this class.
preferences_path = Str
###########################################################################
# 'object' interface.
###########################################################################
def __init__(self, **traits):
""" Constructor. """
super(PreferencesHelper, self).__init__(**traits)
# Initialize the object's traits from the preferences node.
if self.preferences:
self._initialize(self.preferences)
return
###########################################################################
# Private interface.
###########################################################################
#### Trait initializers ###################################################
def _preferences_default(self):
""" Trait initializer. """
# If no specific preferences node is set then we use the package-wide
# global node.
return get_default_preferences()
#### Trait change handlers ################################################
def _anytrait_changed(self, trait_name, old, new):
""" Static trait change handler. """
# If we were the one that set the trait (because the underlying
# preferences node changed) then do nothing.
if self.preferences and self._is_preference_trait(trait_name):
self.preferences.set('%s.%s' % (self._get_path(), trait_name), new)
return
def _preferences_changed(self, old, new):
""" Static trait change handler. """
# Stop listening to the old preferences node.
if old is not None:
old.remove_preferences_listener(
self._preferences_changed_listener, self._get_path()
)
if new is not None:
# Initialize with the new preferences node (this also adds a
# listener for preferences being changed in the new node).
self._initialize(new, notify=True)
return
#### Other observer pattern listeners #####################################
def _preferences_changed_listener(self, node, key, old, new):
""" Listener called when a preference value is changed. """
if key in self.trait_names():
setattr(self, key, self._get_value(key, new))
return
#### Methods ##############################################################
def _get_path(self):
""" Return the path to our preferences node. """
if len(self.preferences_path) > 0:
path = self.preferences_path
else:
path = getattr(self, 'PREFERENCES_PATH', None)
if path is None:
raise SystemError('no preferences path, %s' % self)
else:
logger.warn('DEPRECATED: use "preferences_path" %s' % self)
return path
def _get_value(self, trait_name, value):
""" Get the actual value to set.
This method makes sure that any required work is done to convert the
preference value from a string. Str traits or those with the metadata
'is_str=True' will just be passed the string itself.
"""
trait = self.trait(trait_name)
handler = trait.handler
# If the trait type is 'Str' or Unicode then we just take the raw value.
if isinstance(handler, (Str, Unicode)) or trait.is_str:
pass
# Otherwise, we eval it!
else:
try:
value = eval(value)
# If the eval fails then there is probably a syntax error, but
# we will let the handler validation throw the exception.
except:
pass
if handler.validate is not None:
# Any traits have a validator of None.
validated = handler.validate(self, trait_name, value)
else:
validated = value
return validated
def _initialize(self, preferences, notify=False):
""" Initialize the object's traits from the preferences node. """
path = self._get_path()
keys = preferences.keys(path)
traits_to_set = {}
for trait_name in self.trait_names():
if trait_name in keys:
key = '%s.%s' % (path, trait_name)
value = self._get_value(trait_name, preferences.get(key))
traits_to_set[trait_name] = value
self.set(trait_change_notify=notify, **traits_to_set)
# Listen for changes to the node's preferences.
preferences.add_preferences_listener(
self._preferences_changed_listener, path
)
return
# fixme: Pretty much duplicated in 'PreferencesPage' (except for the
# class name of course!).
def _is_preference_trait(self, trait_name):
""" Return True if a trait represents a preference value. """
if trait_name.startswith('_') or trait_name.endswith('_') \
or trait_name in PreferencesHelper.class_traits():
return False
return True
#### EOF ######################################################################
|
