Warning: This document is for an old version of python-dispatch.

Source code for pydispatch.properties

"""Properties

:class:`Property` objects can be defined on subclasses of
:class:`~pydispatch.Dispatcher` to create instance attributes that act as events
when their values change::

    from pydispatch import Dispatcher, Property

    class Foo(Dispatcher):
        name = Property()
        value = Property()
    def __str__(self):
        return self.__class__.__name__

    class Listener(object):
        def on_foo_name(self, instance, value, **kwargs):
            print("{}'s name is {}".format(instance, value))
        def on_foo_value(self, instance, value, **kwargs):
            print('{} = {}'.format(instance, value))

    foo_obj = Foo()
    listener_obj = Listener()

    foo_obj.bind(name=listener_obj.on_foo_name, value=listener_obj.on_foo_value)

    foo_obj.name = 'bar'
    # Foo's name is bar

    foo_obj.value = 42
    # Foo = 42

Type checking is not enforced, so values can be any valid python type.
Values are however checked for equality to avoid dispatching events for no
reason. If custom objects are used as values, they must be able to support
equality checking. In most cases, this will be handled automatically.
"""

import sys
import weakref

from pydispatch.utils import InformativeWVDict

PY2 = sys.version_info < (3,)

[docs]class Property(object): """Defined on the class level to create an observable attribute Args: default (Optional): If supplied, this will be the default value of the Property for all instances of the class. Otherwise ``None`` Attributes: name (str): The name of the Property as defined in the class definition. This will match the attribute name for the :class:`Dispatcher` instance. """ def __init__(self, default=None): self._name = '' self.default = default self.__storage = {} self.__weakrefs = InformativeWVDict(del_callback=self._on_weakref_fin) @property def name(self): return self._name @name.setter def name(self, value): if self._name != '': return self._name = value def _add_instance(self, obj, default=None): if default is None: default = self.default self.__storage[id(obj)] = self.default self.__weakrefs[id(obj)] = obj def _del_instance(self, obj): del self.__storage[id(obj)] def _on_weakref_fin(self, obj_id): del self.__storage[obj_id] def __get__(self, obj, objcls=None): if obj is None: return self obj_id = id(obj) if obj_id not in self.__storage: self._add_instance(obj) return self.__storage[obj_id] def __set__(self, obj, value): obj_id = id(obj) if obj_id not in self.__storage: self._add_instance(obj) current = self.__storage[obj_id] if current == value: return self.__storage[obj_id] = value self._on_change(obj, current, value)
[docs] def _on_change(self, obj, old, value, **kwargs): """Called internally to emit changes from the instance object The keyword arguments here will be passed to callbacks through the instance object's :meth:`~Dispatcher.emit` method. Keyword Args: property: The :class:`Property` instance. This is useful if multiple properties are bound to the same callback. The attribute name keys (optional): If the :class:`Property` is a container type (:class:`ListProperty` or :class:`DictProperty`), the changes may be found here. This is not implemented for nested containers and will only be available for operations that do not alter the size of the container. """ kwargs['property'] = self obj.emit(self.name, obj, value, old=old, **kwargs)
def __repr__(self): return '<{}: {}>'.format(self.__class__, self) def __str__(self): return self.name
[docs]class ListProperty(Property): """Property with a ``list`` type value Args: default (Optional): If supplied, this will be the default value of the Property for all instances of the class. Otherwise ``None`` copy_on_change (bool, optional): If ``True``, the ``list`` will be copied when contents are modified. This can be useful for observing the original state of the ``list`` from within callbacks. The copied (original) state will be available from the keyword argument 'old'. The default if ``False`` (for performance and memory reasons). Changes to the contents of the list are able to be observed through :class:`ObservableList`. """ def __init__(self, default=None, copy_on_change=False): if default is None: default = [] self.copy_on_change = copy_on_change super(ListProperty, self).__init__(default) def _add_instance(self, obj): default = self.default[:] default = ObservableList(default, obj=obj, property=self) super(ListProperty, self)._add_instance(obj, default) def __set__(self, obj, value): value = ObservableList(value, obj=obj, property=self) super(ListProperty, self).__set__(obj, value) def __get__(self, obj, objcls=None): if obj is None: return self value = super(ListProperty, self).__get__(obj, objcls) if not isinstance(value, ObservableList): value = ObservableList(value, obj=obj, property=self) self._Property__storage[id(obj)] = value return value
[docs]class DictProperty(Property): """Property with a ``dict`` type value Args: default (Optional): If supplied, this will be the default value of the Property for all instances of the class. Otherwise ``None`` copy_on_change (bool, optional): If ``True``, the ``dict`` will be copied when contents are modified. This can be useful for observing the original state of the ``dict`` from within callbacks. The copied (original) state will be available from the keyword argument 'old'. The default if ``False`` (for performance and memory reasons). Changes to the contents of the dict are able to be observed through :class:`ObservableDict`. """ def __init__(self, default=None, copy_on_change=False): if default is None: default = {} self.copy_on_change = copy_on_change super(DictProperty, self).__init__(default) def _add_instance(self, obj): default = self.default.copy() default = ObservableDict(default, obj=obj, property=self) super(DictProperty, self)._add_instance(obj, default) def __set__(self, obj, value): value = ObservableDict(value, obj=obj, property=self) super(DictProperty, self).__set__(obj, value) def __get__(self, obj, objcls=None): if obj is None: return self value = super(DictProperty, self).__get__(obj, objcls) if not isinstance(value, ObservableDict): value = ObservableDict(value, obj=obj, property=self) self._Property__storage[id(obj)] = value return value
class Observable(object): """Used by container subclasses to emit changes and build other observables When an item is added to an observable container (a subclass of Observable) it is type-checked and, if possible replaced by an observable version of it. In other words, if a ``dict`` is added to a :class:`ObservableDict`, it is copied and replaced by another :class:`ObservableDict`. This allows nested containers to be observed and their changes to be tracked. """ def _build_observable(self, item): if isinstance(item, list): item = ObservableList(item, parent=self) elif isinstance(item, dict): item = ObservableDict(item, parent=self) return item def _get_copy_or_none(self): p = self.parent_observable if p is not None: return p._get_copy_or_none() if not self.copy_on_change: return None return self._deepcopy() def _deepcopy(self): o = self.copy() if isinstance(self, list): item_iter = enumerate(self) elif isinstance(self, dict): item_iter = self.items() for key, item in item_iter: if isinstance(item, Observable): o[key] = item._deepcopy() return o def _emit_change(self, **kwargs): if not self._init_complete: return old = kwargs.pop('old') p = self.parent_observable if p is not None: p._emit_change(old=old) return self.property._on_change(self.obj, old, self, **kwargs) class ObservableList(list, Observable): """A ``list`` object that tracks changes to its contents """ def __init__(self, initlist=None, **kwargs): self._init_complete = False super(ObservableList, self).__init__() self.property = kwargs.get('property') self.obj = kwargs.get('obj') self.parent_observable = kwargs.get('parent') if self.property is not None: self.copy_on_change = self.property.copy_on_change else: self.copy_on_change = False if initlist is not None: self.extend(initlist) self._init_complete = True def __setitem__(self, key, item): old = self._get_copy_or_none() item = self._build_observable(item) super(ObservableList, self).__setitem__(key, item) self._emit_change(keys=[key], old=old) def __delitem__(self, key): old = self._get_copy_or_none() super(ObservableList, self).__delitem__(key) self._emit_change(old=old) if PY2: def __setslice__(self, *args): old = self._get_copy_or_none() super(ObservableList, self).__setslice__(*args) self._emit_change(old=old) def __delslice__(self, *args): old = self._get_copy_or_none() super(ObservableList, self).__delslice__(*args) self._emit_change(old=old) if hasattr(list, 'clear'): def clear(self): old = self._get_copy_or_none() super(ObservableList, self).clear() self._emit_change(old=old) if not hasattr(list, 'copy'): def copy(self): return self[:] def __iadd__(self, other): other = self._build_observable(other) self.extend(other) return self def append(self, item): old = self._get_copy_or_none() item = self._build_observable(item) super(ObservableList, self).append(item) self._emit_change(old=old) def extend(self, other): old = self._get_copy_or_none() init = self._init_complete self._init_complete = False for item in other: self.append(item) if init: self._init_complete = True self._emit_change(old=old) def remove(self, *args): old = self._get_copy_or_none() super(ObservableList, self).remove(*args) self._emit_change(old=old) class ObservableDict(dict, Observable): """A ``dict`` object that tracks changes to its contents """ def __init__(self, initdict=None, **kwargs): self._init_complete = False super(ObservableDict, self).__init__() self.property = kwargs.get('property') self.obj = kwargs.get('obj') self.parent_observable = kwargs.get('parent') if self.property is not None: self.copy_on_change = self.property.copy_on_change else: self.copy_on_change = False if initdict is not None: self.update(initdict) self._init_complete = True def __setitem__(self, key, item): old = self._get_copy_or_none() item = self._build_observable(item) super(ObservableDict, self).__setitem__(key, item) self._emit_change(keys=[key], old=old) def __delitem__(self, key): old = self._get_copy_or_none() super(ObservableDict, self).__delitem__(key) self._emit_change(old=old) def update(self, other): old = self._get_copy_or_none() init = self._init_complete self._init_complete = False keys = set(other.keys()) - set(self.keys()) for key, val in other.items(): if key not in keys and self[key] == val: continue self[key] = val keys.add(key) if init: self._init_complete = True self._emit_change(keys=list(keys), old=old) def clear(self): old = self._get_copy_or_none() super(ObservableDict, self).clear() self._emit_change(old=old) def pop(self, *args): old = self._get_copy_or_none() super(ObservableDict, self).pop(*args) self._emit_change(old=old) def setdefault(self, *args): old = self._get_copy_or_none() super(ObservableDict, self).setdefault(*args) self._emit_change(old=old)