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import weakref
import saferef
WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)
def _make_id(target):
if hasattr(target, 'im_func'):
return (id(target.im_self), id(target.im_func))
return id(target)
class Signal(object):
"""Base class for all signals
Internal attributes:
receivers -- { receriverkey (id) : weakref(receiver) }
"""
def __init__(self, providing_args=None):
"""providing_args -- A list of the arguments this signal can pass along
in a send() call.
"""
self.receivers = []
if providing_args is None:
providing_args = []
self.providing_args = set(providing_args)
def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
"""Connect receiver to sender for signal
receiver -- a function or an instance method which is to
receive signals. Receivers must be
hashable objects.
if weak is True, then receiver must be weak-referencable
(more precisely saferef.safeRef() must be able to create
a reference to the receiver).
Receivers must be able to accept keyword arguments.
If receivers have a dispatch_uid attribute, the receiver will
not be added if another receiver already exists with that
dispatch_uid.
sender -- the sender to which the receiver should respond
Must either be of type Signal, or None to receive events
from any sender.
weak -- whether to use weak references to the receiver
By default, the module will attempt to use weak
references to the receiver objects. If this parameter
is false, then strong references will be used.
dispatch_uid -- an identifier used to uniquely identify a particular
instance of a receiver. This will usually be a string, though it
may be anything hashable.
returns None
"""
if dispatch_uid:
lookup_key = (dispatch_uid, _make_id(sender))
else:
lookup_key = (_make_id(receiver), _make_id(sender))
if weak:
receiver = saferef.safeRef(receiver,
onDelete=self._remove_receiver)
for r_key, _ in self.receivers:
if r_key == lookup_key:
break
else:
self.receivers.append((lookup_key, receiver))
def disconnect(self, receiver=None, sender=None, weak=True,
dispatch_uid=None):
"""Disconnect receiver from sender for signal
receiver -- the registered receiver to disconnect. May be none if
dispatch_uid is specified.
sender -- the registered sender to disconnect
weak -- the weakref state to disconnect
dispatch_uid -- the unique identifier of the receiver to disconnect
disconnect reverses the process of connect.
If weak references are used, disconnect need not be called.
The receiver will be remove from dispatch automatically.
returns None
"""
if dispatch_uid:
lookup_key = (dispatch_uid, _make_id(sender))
else:
lookup_key = (_make_id(receiver), _make_id(sender))
for idx, (r_key, _) in enumerate(self.receivers):
if r_key == lookup_key:
del self.receivers[idx]
def send(self, sender, **named):
"""Send signal from sender to all connected receivers.
sender -- the sender of the signal
Either a specific object or None.
named -- named arguments which will be passed to receivers.
Returns a list of tuple pairs [(receiver, response), ... ].
If any receiver raises an error, the error propagates back
through send, terminating the dispatch loop, so it is quite
possible to not have all receivers called if a raises an
error.
"""
responses = []
if not self.receivers:
return responses
for receiver in self._live_receivers(_make_id(sender)):
response = receiver(signal=self, sender=sender, **named)
responses.append((receiver, response))
return responses
def send_robust(self, sender, **named):
"""Send signal from sender to all connected receivers catching errors
sender -- the sender of the signal
Can be any python object (normally one registered with
a connect if you actually want something to occur).
named -- named arguments which will be passed to receivers.
These arguments must be a subset of the argument names
defined in providing_args.
Return a list of tuple pairs [(receiver, response), ... ],
may raise DispatcherKeyError
if any receiver raises an error (specifically any subclass of
Exception), the error instance is returned as the result for that
receiver.
"""
responses = []
if not self.receivers:
return responses
# Call each receiver with whatever arguments it can accept.
# Return a list of tuple pairs [(receiver, response), ... ].
for receiver in self._live_receivers(_make_id(sender)):
try:
response = receiver(signal=self, sender=sender, **named)
except Exception, err:
responses.append((receiver, err))
else:
responses.append((receiver, response))
return responses
def _live_receivers(self, senderkey):
"""Filter sequence of receivers to get resolved, live receivers
This checks for weak references
and resolves them, then returning only live
receivers.
"""
none_senderkey = _make_id(None)
for (receiverkey_, r_senderkey), receiver in self.receivers:
if r_senderkey == none_senderkey or r_senderkey == senderkey:
if isinstance(receiver, WEAKREF_TYPES):
# Dereference the weak reference.
receiver = receiver()
if receiver is not None:
yield receiver
else:
yield receiver
def _remove_receiver(self, receiver):
"""Remove dead receivers from connections."""
to_remove = []
for key, connected_receiver in self.receivers:
if connected_receiver == receiver:
to_remove.append(key)
for key in to_remove:
for idx, (r_key, _) in enumerate(self.receivers):
if r_key == key:
del self.receivers[idx]
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