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import weakref
from functools import partial
__all__ = ['CallbackContainer']
class CallbackContainer(object):
"""
A list-like container for callback functions. We need to be careful with
storing references to methods, because if a callback method is on a class
which contains both the callback and a callback property, a circular
reference is created which results in a memory leak. Instead, we need to use
a weak reference which results in the callback being removed if the instance
is destroyed. This container class takes care of this automatically.
"""
def __init__(self):
self.callbacks = []
def clear(self):
self.callbacks[:] = []
def _wrap(self, value, priority=0):
"""
Given a function/method, this will automatically wrap a method using
weakref to avoid circular references.
"""
if not callable(value):
raise TypeError("Only callable values can be stored in CallbackContainer")
elif self.is_bound_method(value):
# We are dealing with a bound method. Method references aren't
# persistent, so instead we store a reference to the function
# and instance.
value = (weakref.ref(value.__func__),
weakref.ref(value.__self__, self._auto_remove),
priority)
else:
value = (value, priority)
return value
def _auto_remove(self, method_instance):
# Called when weakref detects that the instance on which a method was
# defined has been garbage collected.
for value in self.callbacks[:]:
if isinstance(value, tuple) and value[1] is method_instance:
self.callbacks.remove(value)
def __contains__(self, value):
if self.is_bound_method(value):
for callback in self.callbacks[:]:
if len(callback) == 3 and value.__func__ is callback[0]() and value.__self__ is callback[1]():
return True
else:
return False
else:
for callback in self.callbacks[:]:
if len(callback) == 2 and value is callback[0]:
return True
else:
return False
def __iter__(self):
for callback in sorted(self.callbacks, key=lambda x: x[-1], reverse=True):
if len(callback) == 3:
func = callback[0]()
inst = callback[1]()
# In some cases it can happen that the instance has been
# garbage collected but _auto_remove hasn't been called, so we
# just check here that the weakrefs were resolved
if func is None or inst is None:
continue
yield partial(func, inst)
else:
yield callback[0]
def __len__(self):
return len(self.callbacks)
@staticmethod
def is_bound_method(func):
return hasattr(func, '__func__') and getattr(func, '__self__', None) is not None
def append(self, value, priority=0):
self.callbacks.append(self._wrap(value, priority=priority))
def remove(self, value):
if self.is_bound_method(value):
for callback in self.callbacks[:]:
if len(callback) == 3 and value.__func__ is callback[0]() and value.__self__ is callback[1]():
self.callbacks.remove(callback)
else:
for callback in self.callbacks[:]:
if len(callback) == 2 and value is callback[0]:
self.callbacks.remove(callback)
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