293 lines
10 KiB
Python
293 lines
10 KiB
Python
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import threading
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import weakref
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from django.utils.inspect import func_accepts_kwargs
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def _make_id(target):
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if hasattr(target, '__func__'):
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return (id(target.__self__), id(target.__func__))
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return id(target)
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NONE_ID = _make_id(None)
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# A marker for caching
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NO_RECEIVERS = object()
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class Signal:
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"""
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Base class for all signals
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Internal attributes:
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receivers
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{ receiverkey (id) : weakref(receiver) }
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"""
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def __init__(self, providing_args=None, use_caching=False):
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"""
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Create a new signal.
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providing_args
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A list of the arguments this signal can pass along in a send() call.
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"""
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self.receivers = []
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if providing_args is None:
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providing_args = []
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self.providing_args = set(providing_args)
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self.lock = threading.Lock()
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self.use_caching = use_caching
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# For convenience we create empty caches even if they are not used.
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# A note about caching: if use_caching is defined, then for each
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# distinct sender we cache the receivers that sender has in
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# 'sender_receivers_cache'. The cache is cleaned when .connect() or
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# .disconnect() is called and populated on send().
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self.sender_receivers_cache = weakref.WeakKeyDictionary() if use_caching else {}
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self._dead_receivers = False
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def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
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"""
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Connect receiver to sender for signal.
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Arguments:
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receiver
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A function or an instance method which is to receive signals.
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Receivers must be hashable objects.
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If weak is True, then receiver must be weak referenceable.
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Receivers must be able to accept keyword arguments.
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If a receiver is connected with a dispatch_uid argument, it
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will not be added if another receiver was already connected
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with that dispatch_uid.
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sender
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The sender to which the receiver should respond. Must either be
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a Python object, or None to receive events from any sender.
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weak
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Whether to use weak references to the receiver. By default, the
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module will attempt to use weak references to the receiver
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objects. If this parameter is false, then strong references will
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be used.
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dispatch_uid
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An identifier used to uniquely identify a particular instance of
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a receiver. This will usually be a string, though it may be
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anything hashable.
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"""
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from django.conf import settings
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# If DEBUG is on, check that we got a good receiver
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if settings.configured and settings.DEBUG:
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assert callable(receiver), "Signal receivers must be callable."
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# Check for **kwargs
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if not func_accepts_kwargs(receiver):
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raise ValueError("Signal receivers must accept keyword arguments (**kwargs).")
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if dispatch_uid:
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lookup_key = (dispatch_uid, _make_id(sender))
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else:
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lookup_key = (_make_id(receiver), _make_id(sender))
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if weak:
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ref = weakref.ref
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receiver_object = receiver
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# Check for bound methods
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if hasattr(receiver, '__self__') and hasattr(receiver, '__func__'):
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ref = weakref.WeakMethod
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receiver_object = receiver.__self__
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receiver = ref(receiver)
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weakref.finalize(receiver_object, self._remove_receiver)
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with self.lock:
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self._clear_dead_receivers()
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if not any(r_key == lookup_key for r_key, _ in self.receivers):
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self.receivers.append((lookup_key, receiver))
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self.sender_receivers_cache.clear()
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def disconnect(self, receiver=None, sender=None, dispatch_uid=None):
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"""
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Disconnect receiver from sender for signal.
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If weak references are used, disconnect need not be called. The receiver
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will be removed from dispatch automatically.
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Arguments:
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receiver
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The registered receiver to disconnect. May be none if
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dispatch_uid is specified.
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sender
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The registered sender to disconnect
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dispatch_uid
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the unique identifier of the receiver to disconnect
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"""
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if dispatch_uid:
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lookup_key = (dispatch_uid, _make_id(sender))
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else:
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lookup_key = (_make_id(receiver), _make_id(sender))
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disconnected = False
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with self.lock:
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self._clear_dead_receivers()
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for index in range(len(self.receivers)):
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(r_key, _) = self.receivers[index]
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if r_key == lookup_key:
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disconnected = True
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del self.receivers[index]
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break
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self.sender_receivers_cache.clear()
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return disconnected
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def has_listeners(self, sender=None):
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return bool(self._live_receivers(sender))
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def send(self, sender, **named):
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"""
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Send signal from sender to all connected receivers.
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If any receiver raises an error, the error propagates back through send,
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terminating the dispatch loop. So it's possible that all receivers
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won't be called if an error is raised.
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Arguments:
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sender
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The sender of the signal. Either a specific object or None.
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named
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Named arguments which will be passed to receivers.
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Return a list of tuple pairs [(receiver, response), ... ].
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"""
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if not self.receivers or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:
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return []
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return [
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(receiver, receiver(signal=self, sender=sender, **named))
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for receiver in self._live_receivers(sender)
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]
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def send_robust(self, sender, **named):
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"""
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Send signal from sender to all connected receivers catching errors.
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Arguments:
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sender
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The sender of the signal. Can be any Python object (normally one
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registered with a connect if you actually want something to
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occur).
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named
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Named arguments which will be passed to receivers. These
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arguments must be a subset of the argument names defined in
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providing_args.
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Return a list of tuple pairs [(receiver, response), ... ].
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If any receiver raises an error (specifically any subclass of
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Exception), return the error instance as the result for that receiver.
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"""
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if not self.receivers or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:
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return []
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# Call each receiver with whatever arguments it can accept.
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# Return a list of tuple pairs [(receiver, response), ... ].
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responses = []
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for receiver in self._live_receivers(sender):
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try:
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response = receiver(signal=self, sender=sender, **named)
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except Exception as err:
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responses.append((receiver, err))
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else:
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responses.append((receiver, response))
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return responses
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def _clear_dead_receivers(self):
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# Note: caller is assumed to hold self.lock.
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if self._dead_receivers:
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self._dead_receivers = False
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self.receivers = [
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r for r in self.receivers
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if not(isinstance(r[1], weakref.ReferenceType) and r[1]() is None)
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]
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def _live_receivers(self, sender):
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"""
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Filter sequence of receivers to get resolved, live receivers.
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This checks for weak references and resolves them, then returning only
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live receivers.
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"""
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receivers = None
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if self.use_caching and not self._dead_receivers:
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receivers = self.sender_receivers_cache.get(sender)
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# We could end up here with NO_RECEIVERS even if we do check this case in
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# .send() prior to calling _live_receivers() due to concurrent .send() call.
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if receivers is NO_RECEIVERS:
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return []
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if receivers is None:
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with self.lock:
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self._clear_dead_receivers()
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senderkey = _make_id(sender)
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receivers = []
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for (receiverkey, r_senderkey), receiver in self.receivers:
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if r_senderkey == NONE_ID or r_senderkey == senderkey:
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receivers.append(receiver)
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if self.use_caching:
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if not receivers:
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self.sender_receivers_cache[sender] = NO_RECEIVERS
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else:
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# Note, we must cache the weakref versions.
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self.sender_receivers_cache[sender] = receivers
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non_weak_receivers = []
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for receiver in receivers:
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if isinstance(receiver, weakref.ReferenceType):
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# Dereference the weak reference.
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receiver = receiver()
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if receiver is not None:
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non_weak_receivers.append(receiver)
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else:
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non_weak_receivers.append(receiver)
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return non_weak_receivers
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def _remove_receiver(self, receiver=None):
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# Mark that the self.receivers list has dead weakrefs. If so, we will
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# clean those up in connect, disconnect and _live_receivers while
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# holding self.lock. Note that doing the cleanup here isn't a good
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# idea, _remove_receiver() will be called as side effect of garbage
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# collection, and so the call can happen while we are already holding
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# self.lock.
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self._dead_receivers = True
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def receiver(signal, **kwargs):
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"""
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A decorator for connecting receivers to signals. Used by passing in the
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signal (or list of signals) and keyword arguments to connect::
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@receiver(post_save, sender=MyModel)
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def signal_receiver(sender, **kwargs):
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...
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@receiver([post_save, post_delete], sender=MyModel)
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def signals_receiver(sender, **kwargs):
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...
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"""
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def _decorator(func):
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if isinstance(signal, (list, tuple)):
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for s in signal:
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s.connect(func, **kwargs)
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else:
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signal.connect(func, **kwargs)
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return func
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return _decorator
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