from eventstreamr2.utils.collections import WeakFunctionCollection
[docs]class Observable(object):
"""
An mixin object that provides an event listener style interface.
.. note::
It is reccomended that :meth:`add_weak_observer` is used whenever possible as it handles
cleanup better than it's strong counterpart.
.. note::
:code:`remove_weak_observer` is missing intentionally; Primarily because it is unlikely to
be needed; and secondly because it is hard to implement a remove method inside
:class:`WeakFunctionCollection`.
"""
def __init__(self, *args, **kwargs):
"""
Setup the observable. All arguments are passed on to a super call.
"""
super(Observable, self).__init__(*args, **kwargs)
self._observers = list()
self._weak_observers = WeakFunctionCollection()
[docs] def add_observer(self, fn):
"""
Add an observer function.
"""
self._observers.append(fn)
[docs] def add_weak_observer(self, fn):
"""
Add an observer function that is stored weakly. This means that when the given function
leaves scope, it will no longer be called. Special handling is done on bound methods to
ensure that they are not removed until the object they are bound on leaves scope.
"""
self._weak_observers.append(fn)
[docs] def remove_observer(self, fn):
"""
Remove an observer function.
"""
self._observers.remove(fn)
[docs] def _notify_observers(self, *args, **kwargs):
"""
Notify all existing observers, or more specifically call each observer with any
arguments(both positional and keyword) passed in.
All listeners defined at the start of this method's execution will be called and any
changes afterwards will not affect this method call.
"""
# The weak functions won't be garbage collected because they are saved in the list below.
# This makes the
listeners = list(self._observers) + list(self._weak_observers)
for fn in listeners:
fn(*args, **kwargs)