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#!/usr/bin/env python
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# encoding: utf-8
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"""
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A lightweight component system for IPython.
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Authors:
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* Brian Granger
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* Fernando Perez
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"""
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#-----------------------------------------------------------------------------
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# Copyright (C) 2008-2009 The IPython Development Team
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#
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# Distributed under the terms of the BSD License. The full license is in
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# the file COPYING, distributed as part of this software.
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#-----------------------------------------------------------------------------
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#-----------------------------------------------------------------------------
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# Imports
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#-----------------------------------------------------------------------------
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from copy import deepcopy
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import datetime
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from weakref import WeakValueDictionary
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from IPython.utils.importstring import import_item
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from IPython.config.loader import Config
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from IPython.utils.traitlets import (
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HasTraitlets, TraitletError, MetaHasTraitlets, Instance, This
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)
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#-----------------------------------------------------------------------------
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# Helper classes for Components
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#-----------------------------------------------------------------------------
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class ComponentError(Exception):
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pass
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class MetaComponentTracker(type):
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"""A metaclass that tracks instances of Components and its subclasses."""
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def __init__(cls, name, bases, d):
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super(MetaComponentTracker, cls).__init__(name, bases, d)
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cls.__instance_refs = WeakValueDictionary()
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cls.__numcreated = 0
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def __call__(cls, *args, **kw):
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"""Called when a class is called (instantiated)!!!
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When a Component or subclass is instantiated, this is called and
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the instance is saved in a WeakValueDictionary for tracking.
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"""
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instance = cls.__new__(cls, *args, **kw)
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# Register the instance before __init__ is called so get_instances
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# works inside __init__ methods!
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indices = cls.register_instance(instance)
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# This is in a try/except because of the __init__ method fails, the
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# instance is discarded and shouldn't be tracked.
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try:
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if isinstance(instance, cls):
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cls.__init__(instance, *args, **kw)
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except:
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# Unregister the instance because __init__ failed!
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cls.unregister_instances(indices)
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raise
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else:
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return instance
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def register_instance(cls, instance):
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"""Register instance with cls and its subclasses."""
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# indices is a list of the keys used to register the instance
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# with. This list is needed if the instance needs to be unregistered.
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indices = []
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for c in cls.__mro__:
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if issubclass(cls, c) and issubclass(c, Component):
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c.__numcreated += 1
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indices.append(c.__numcreated)
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c.__instance_refs[c.__numcreated] = instance
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else:
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break
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return indices
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def unregister_instances(cls, indices):
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"""Unregister instance with cls and its subclasses."""
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for c, index in zip(cls.__mro__, indices):
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try:
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del c.__instance_refs[index]
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except KeyError:
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pass
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def clear_instances(cls):
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"""Clear all instances tracked by cls."""
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cls.__instance_refs.clear()
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cls.__numcreated = 0
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def get_instances(cls, name=None, root=None, klass=None):
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"""Get all instances of cls and its subclasses.
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Parameters
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----------
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name : str
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Limit to components with this name.
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root : Component or subclass
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Limit to components having this root.
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klass : class or str
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Limits to instances of the class or its subclasses. If a str
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is given ut must be in the form 'foo.bar.MyClass'. The str
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form of this argument is useful for forward declarations.
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"""
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if klass is not None:
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if isinstance(klass, basestring):
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klass = import_item(klass)
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# Limit search to instances of klass for performance
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if issubclass(klass, Component):
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return klass.get_instances(name=name, root=root)
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instances = cls.__instance_refs.values()
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if name is not None:
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instances = [i for i in instances if i.name == name]
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if klass is not None:
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instances = [i for i in instances if isinstance(i, klass)]
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if root is not None:
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instances = [i for i in instances if i.root == root]
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return instances
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def get_instances_by_condition(cls, call, name=None, root=None,
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klass=None):
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"""Get all instances of cls, i such that call(i)==True.
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This also takes the ``name`` and ``root`` and ``classname``
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arguments of :meth:`get_instance`
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"""
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return [i for i in cls.get_instances(name, root, klass) if call(i)]
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def masquerade_as(instance, cls):
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"""Let instance masquerade as an instance of cls.
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Sometimes, such as in testing code, it is useful to let a class
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masquerade as another. Python, being duck typed, allows this by
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default. But, instances of components are tracked by their class type.
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After calling this, ``cls.get_instances()`` will return ``instance``. This
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does not, however, cause ``isinstance(instance, cls)`` to return ``True``.
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Parameters
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----------
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instance : an instance of a Component or Component subclass
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The instance that will pretend to be a cls.
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cls : subclass of Component
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The Component subclass that instance will pretend to be.
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"""
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cls.register_instance(instance)
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class __ComponentNameGenerator(object):
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"""A Singleton to generate unique component names."""
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def __init__(self, prefix):
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self.prefix = prefix
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self.i = 0
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def __call__(self):
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count = self.i
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self.i += 1
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return "%s%s" % (self.prefix, count)
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ComponentNameGenerator = __ComponentNameGenerator('ipython.component')
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class MetaComponent(MetaHasTraitlets, MetaComponentTracker):
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pass
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#-----------------------------------------------------------------------------
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# Component implementation
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#-----------------------------------------------------------------------------
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class Component(HasTraitlets):
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__metaclass__ = MetaComponent
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# Traitlets are fun!
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config = Instance(Config,(),{})
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parent = This()
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root = This()
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created = None
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def __init__(self, parent, name=None, config=None):
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"""Create a component given a parent and possibly and name and config.
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Parameters
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----------
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parent : Component subclass
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The parent in the component graph. The parent is used
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to get the root of the component graph.
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name : str
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The unique name of the component. If empty, then a unique
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one will be autogenerated.
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config : Config
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If this is empty, self.config = parent.config, otherwise
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self.config = config and root.config is ignored. This argument
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should only be used to *override* the automatic inheritance of
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parent.config. If a caller wants to modify parent.config
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(not override), the caller should make a copy and change
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attributes and then pass the copy to this argument.
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Notes
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-----
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Subclasses of Component must call the :meth:`__init__` method of
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:class:`Component` *before* doing anything else and using
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:func:`super`::
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class MyComponent(Component):
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def __init__(self, parent, name=None, config=None):
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super(MyComponent, self).__init__(parent, name, config)
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# Then any other code you need to finish initialization.
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This ensures that the :attr:`parent`, :attr:`name` and :attr:`config`
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attributes are handled properly.
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"""
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super(Component, self).__init__()
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self._children = []
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if name is None:
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self.name = ComponentNameGenerator()
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else:
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self.name = name
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self.root = self # This is the default, it is set when parent is set
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self.parent = parent
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if config is not None:
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self.config = config
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# We used to deepcopy, but for now we are trying to just save
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# by reference. This *could* have side effects as all components
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# will share config. In fact, I did find such a side effect in
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# _config_changed below. If a config attribute value was a mutable type
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# all instances of a component were getting the same copy, effectively
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# making that a class attribute.
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# self.config = deepcopy(config)
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else:
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if self.parent is not None:
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self.config = self.parent.config
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# We used to deepcopy, but for now we are trying to just save
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# by reference. This *could* have side effects as all components
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# will share config. In fact, I did find such a side effect in
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# _config_changed below. If a config attribute value was a mutable type
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# all instances of a component were getting the same copy, effectively
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# making that a class attribute.
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# self.config = deepcopy(self.parent.config)
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self.created = datetime.datetime.now()
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#-------------------------------------------------------------------------
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# Static traitlet notifiations
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#-------------------------------------------------------------------------
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def _parent_changed(self, name, old, new):
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if old is not None:
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old._remove_child(self)
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if new is not None:
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new._add_child(self)
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if new is None:
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self.root = self
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else:
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self.root = new.root
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def _root_changed(self, name, old, new):
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if self.parent is None:
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if not (new is self):
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raise ComponentError("Root not self, but parent is None.")
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else:
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if not self.parent.root is new:
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raise ComponentError("Error in setting the root attribute: "
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"root != parent.root")
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def _config_changed(self, name, old, new):
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"""Update all the class traits having ``config=True`` as metadata.
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For any class traitlet with a ``config`` metadata attribute that is
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``True``, we update the traitlet with the value of the corresponding
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config entry.
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"""
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# Get all traitlets with a config metadata entry that is True
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traitlets = self.traitlets(config=True)
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# We auto-load config section for this class as well as any parent
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# classes that are Component subclasses. This starts with Component
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# and works down the mro loading the config for each section.
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section_names = [cls.__name__ for cls in \
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reversed(self.__class__.__mro__) if
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issubclass(cls, Component) and issubclass(self.__class__, cls)]
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for sname in section_names:
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# Don't do a blind getattr as that would cause the config to
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# dynamically create the section with name self.__class__.__name__.
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if new._has_section(sname):
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my_config = new[sname]
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for k, v in traitlets.items():
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# Don't allow traitlets with config=True to start with
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# uppercase. Otherwise, they are confused with Config
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# subsections. But, developers shouldn't have uppercase
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# attributes anyways! (PEP 6)
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if k[0].upper()==k[0] and not k.startswith('_'):
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raise ComponentError('Component traitlets with '
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'config=True must start with a lowercase so they are '
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'not confused with Config subsections: %s.%s' % \
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(self.__class__.__name__, k))
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try:
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# Here we grab the value from the config
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# If k has the naming convention of a config
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# section, it will be auto created.
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config_value = my_config[k]
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except KeyError:
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pass
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else:
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# print "Setting %s.%s from %s.%s=%r" % \
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# (self.__class__.__name__,k,sname,k,config_value)
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# We have to do a deepcopy here if we don't deepcopy the entire
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# config object. If we don't, a mutable config_value will be
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# shared by all instances, effectively making it a class attribute.
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setattr(self, k, deepcopy(config_value))
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@property
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def children(self):
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"""A list of all my child components."""
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return self._children
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def _remove_child(self, child):
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"""A private method for removing children components."""
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if child in self._children:
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index = self._children.index(child)
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del self._children[index]
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def _add_child(self, child):
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"""A private method for adding children components."""
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if child not in self._children:
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self._children.append(child)
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def __repr__(self):
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return "<%s('%s')>" % (self.__class__.__name__, self.name)
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