427 lines
14 KiB
Python
427 lines
14 KiB
Python
|
# -*- coding: utf-8; fill-column: 76 -*-
|
||
|
|
"""Signals and events.
|
||
|
|
|
||
|
|
A small implementation of signals, inspired by a snippet of Django signal
|
||
|
|
API client code seen in a blog post. Signals are first-class objects and
|
||
|
|
each manages its own receivers and message emission.
|
||
|
|
|
||
|
|
The :func:`signal` function provides singleton behavior for named signals.
|
||
|
|
|
||
|
|
"""
|
||
|
|
from warnings import warn
|
||
|
|
from weakref import WeakValueDictionary
|
||
|
|
|
||
|
|
from blinker._utilities import (
|
||
|
|
WeakTypes,
|
||
|
|
contextmanager,
|
||
|
|
defaultdict,
|
||
|
|
hashable_identity,
|
||
|
|
lazy_property,
|
||
|
|
reference,
|
||
|
|
symbol,
|
||
|
|
)
|
||
|
|
|
||
|
|
|
||
|
|
ANY = symbol('ANY')
|
||
|
|
ANY.__doc__ = 'Token for "any sender".'
|
||
|
|
ANY_ID = 0
|
||
|
|
|
||
|
|
|
||
|
|
class Signal(object):
|
||
|
|
"""A notification emitter."""
|
||
|
|
|
||
|
|
#: An :obj:`ANY` convenience synonym, allows ``Signal.ANY``
|
||
|
|
#: without an additional import.
|
||
|
|
ANY = ANY
|
||
|
|
|
||
|
|
@lazy_property
|
||
|
|
def receiver_connected(self):
|
||
|
|
"""Emitted after each :meth:`connect`.
|
||
|
|
|
||
|
|
The signal sender is the signal instance, and the :meth:`connect`
|
||
|
|
arguments are passed through: *receiver*, *sender*, and *weak*.
|
||
|
|
|
||
|
|
.. versionadded:: 1.2
|
||
|
|
|
||
|
|
"""
|
||
|
|
return Signal(doc="Emitted after a receiver connects.")
|
||
|
|
|
||
|
|
@lazy_property
|
||
|
|
def receiver_disconnected(self):
|
||
|
|
"""Emitted after :meth:`disconnect`.
|
||
|
|
|
||
|
|
The sender is the signal instance, and the :meth:`disconnect` arguments
|
||
|
|
are passed through: *receiver* and *sender*.
|
||
|
|
|
||
|
|
Note, this signal is emitted **only** when :meth:`disconnect` is
|
||
|
|
called explicitly.
|
||
|
|
|
||
|
|
The disconnect signal can not be emitted by an automatic disconnect
|
||
|
|
(due to a weakly referenced receiver or sender going out of scope),
|
||
|
|
as the receiver and/or sender instances are no longer available for
|
||
|
|
use at the time this signal would be emitted.
|
||
|
|
|
||
|
|
An alternative approach is available by subscribing to
|
||
|
|
:attr:`receiver_connected` and setting up a custom weakref cleanup
|
||
|
|
callback on weak receivers and senders.
|
||
|
|
|
||
|
|
.. versionadded:: 1.2
|
||
|
|
|
||
|
|
"""
|
||
|
|
return Signal(doc="Emitted after a receiver disconnects.")
|
||
|
|
|
||
|
|
def __init__(self, doc=None):
|
||
|
|
"""
|
||
|
|
:param doc: optional. If provided, will be assigned to the signal's
|
||
|
|
__doc__ attribute.
|
||
|
|
|
||
|
|
"""
|
||
|
|
if doc:
|
||
|
|
self.__doc__ = doc
|
||
|
|
#: A mapping of connected receivers.
|
||
|
|
#:
|
||
|
|
#: The values of this mapping are not meaningful outside of the
|
||
|
|
#: internal :class:`Signal` implementation, however the boolean value
|
||
|
|
#: of the mapping is useful as an extremely efficient check to see if
|
||
|
|
#: any receivers are connected to the signal.
|
||
|
|
self.receivers = {}
|
||
|
|
self._by_receiver = defaultdict(set)
|
||
|
|
self._by_sender = defaultdict(set)
|
||
|
|
self._weak_senders = {}
|
||
|
|
|
||
|
|
def connect(self, receiver, sender=ANY, weak=True):
|
||
|
|
"""Connect *receiver* to signal events sent by *sender*.
|
||
|
|
|
||
|
|
:param receiver: A callable. Will be invoked by :meth:`send` with
|
||
|
|
`sender=` as a single positional argument and any \*\*kwargs that
|
||
|
|
were provided to a call to :meth:`send`.
|
||
|
|
|
||
|
|
:param sender: Any object or :obj:`ANY`, defaults to ``ANY``.
|
||
|
|
Restricts notifications delivered to *receiver* to only those
|
||
|
|
:meth:`send` emissions sent by *sender*. If ``ANY``, the receiver
|
||
|
|
will always be notified. A *receiver* may be connected to
|
||
|
|
multiple *sender* values on the same Signal through multiple calls
|
||
|
|
to :meth:`connect`.
|
||
|
|
|
||
|
|
:param weak: If true, the Signal will hold a weakref to *receiver*
|
||
|
|
and automatically disconnect when *receiver* goes out of scope or
|
||
|
|
is garbage collected. Defaults to True.
|
||
|
|
|
||
|
|
"""
|
||
|
|
receiver_id = hashable_identity(receiver)
|
||
|
|
if weak:
|
||
|
|
receiver_ref = reference(receiver, self._cleanup_receiver)
|
||
|
|
receiver_ref.receiver_id = receiver_id
|
||
|
|
else:
|
||
|
|
receiver_ref = receiver
|
||
|
|
if sender is ANY:
|
||
|
|
sender_id = ANY_ID
|
||
|
|
else:
|
||
|
|
sender_id = hashable_identity(sender)
|
||
|
|
|
||
|
|
self.receivers.setdefault(receiver_id, receiver_ref)
|
||
|
|
self._by_sender[sender_id].add(receiver_id)
|
||
|
|
self._by_receiver[receiver_id].add(sender_id)
|
||
|
|
del receiver_ref
|
||
|
|
|
||
|
|
if sender is not ANY and sender_id not in self._weak_senders:
|
||
|
|
# wire together a cleanup for weakref-able senders
|
||
|
|
try:
|
||
|
|
sender_ref = reference(sender, self._cleanup_sender)
|
||
|
|
sender_ref.sender_id = sender_id
|
||
|
|
except TypeError:
|
||
|
|
pass
|
||
|
|
else:
|
||
|
|
self._weak_senders.setdefault(sender_id, sender_ref)
|
||
|
|
del sender_ref
|
||
|
|
|
||
|
|
# broadcast this connection. if receivers raise, disconnect.
|
||
|
|
if ('receiver_connected' in self.__dict__ and
|
||
|
|
self.receiver_connected.receivers):
|
||
|
|
try:
|
||
|
|
self.receiver_connected.send(self,
|
||
|
|
receiver=receiver,
|
||
|
|
sender=sender,
|
||
|
|
weak=weak)
|
||
|
|
except:
|
||
|
|
self.disconnect(receiver, sender)
|
||
|
|
raise
|
||
|
|
if receiver_connected.receivers and self is not receiver_connected:
|
||
|
|
try:
|
||
|
|
receiver_connected.send(self,
|
||
|
|
receiver_arg=receiver,
|
||
|
|
sender_arg=sender,
|
||
|
|
weak_arg=weak)
|
||
|
|
except:
|
||
|
|
self.disconnect(receiver, sender)
|
||
|
|
raise
|
||
|
|
return receiver
|
||
|
|
|
||
|
|
def connect_via(self, sender, weak=False):
|
||
|
|
"""Connect the decorated function as a receiver for *sender*.
|
||
|
|
|
||
|
|
:param sender: Any object or :obj:`ANY`. The decorated function
|
||
|
|
will only receive :meth:`send` emissions sent by *sender*. If
|
||
|
|
``ANY``, the receiver will always be notified. A function may be
|
||
|
|
decorated multiple times with differing *sender* values.
|
||
|
|
|
||
|
|
:param weak: If true, the Signal will hold a weakref to the
|
||
|
|
decorated function and automatically disconnect when *receiver*
|
||
|
|
goes out of scope or is garbage collected. Unlike
|
||
|
|
:meth:`connect`, this defaults to False.
|
||
|
|
|
||
|
|
The decorated function will be invoked by :meth:`send` with
|
||
|
|
`sender=` as a single positional argument and any \*\*kwargs that
|
||
|
|
were provided to the call to :meth:`send`.
|
||
|
|
|
||
|
|
|
||
|
|
.. versionadded:: 1.1
|
||
|
|
|
||
|
|
"""
|
||
|
|
def decorator(fn):
|
||
|
|
self.connect(fn, sender, weak)
|
||
|
|
return fn
|
||
|
|
return decorator
|
||
|
|
|
||
|
|
@contextmanager
|
||
|
|
def connected_to(self, receiver, sender=ANY):
|
||
|
|
"""Execute a block with the signal temporarily connected to *receiver*.
|
||
|
|
|
||
|
|
:param receiver: a receiver callable
|
||
|
|
:param sender: optional, a sender to filter on
|
||
|
|
|
||
|
|
This is a context manager for use in the ``with`` statement. It can
|
||
|
|
be useful in unit tests. *receiver* is connected to the signal for
|
||
|
|
the duration of the ``with`` block, and will be disconnected
|
||
|
|
automatically when exiting the block:
|
||
|
|
|
||
|
|
.. testsetup::
|
||
|
|
|
||
|
|
from __future__ import with_statement
|
||
|
|
from blinker import Signal
|
||
|
|
on_ready = Signal()
|
||
|
|
receiver = lambda sender: None
|
||
|
|
|
||
|
|
.. testcode::
|
||
|
|
|
||
|
|
with on_ready.connected_to(receiver):
|
||
|
|
# do stuff
|
||
|
|
on_ready.send(123)
|
||
|
|
|
||
|
|
.. versionadded:: 1.1
|
||
|
|
|
||
|
|
"""
|
||
|
|
self.connect(receiver, sender=sender, weak=False)
|
||
|
|
try:
|
||
|
|
yield None
|
||
|
|
except:
|
||
|
|
self.disconnect(receiver)
|
||
|
|
raise
|
||
|
|
else:
|
||
|
|
self.disconnect(receiver)
|
||
|
|
|
||
|
|
def temporarily_connected_to(self, receiver, sender=ANY):
|
||
|
|
"""An alias for :meth:`connected_to`.
|
||
|
|
|
||
|
|
:param receiver: a receiver callable
|
||
|
|
:param sender: optional, a sender to filter on
|
||
|
|
|
||
|
|
.. versionadded:: 0.9
|
||
|
|
|
||
|
|
.. versionchanged:: 1.1
|
||
|
|
Renamed to :meth:`connected_to`. ``temporarily_connected_to``
|
||
|
|
was deprecated in 1.2 and removed in a subsequent version.
|
||
|
|
|
||
|
|
"""
|
||
|
|
warn("temporarily_connected_to is deprecated; "
|
||
|
|
"use connected_to instead.",
|
||
|
|
DeprecationWarning)
|
||
|
|
return self.connected_to(receiver, sender)
|
||
|
|
|
||
|
|
def send(self, *sender, **kwargs):
|
||
|
|
"""Emit this signal on behalf of *sender*, passing on \*\*kwargs.
|
||
|
|
|
||
|
|
Returns a list of 2-tuples, pairing receivers with their return
|
||
|
|
value. The ordering of receiver notification is undefined.
|
||
|
|
|
||
|
|
:param \*sender: Any object or ``None``. If omitted, synonymous
|
||
|
|
with ``None``. Only accepts one positional argument.
|
||
|
|
|
||
|
|
:param \*\*kwargs: Data to be sent to receivers.
|
||
|
|
|
||
|
|
"""
|
||
|
|
# Using '*sender' rather than 'sender=None' allows 'sender' to be
|
||
|
|
# used as a keyword argument- i.e. it's an invisible name in the
|
||
|
|
# function signature.
|
||
|
|
if len(sender) == 0:
|
||
|
|
sender = None
|
||
|
|
elif len(sender) > 1:
|
||
|
|
raise TypeError('send() accepts only one positional argument, '
|
||
|
|
'%s given' % len(sender))
|
||
|
|
else:
|
||
|
|
sender = sender[0]
|
||
|
|
if not self.receivers:
|
||
|
|
return []
|
||
|
|
else:
|
||
|
|
return [(receiver, receiver(sender, **kwargs))
|
||
|
|
for receiver in self.receivers_for(sender)]
|
||
|
|
|
||
|
|
def has_receivers_for(self, sender):
|
||
|
|
"""True if there is probably a receiver for *sender*.
|
||
|
|
|
||
|
|
Performs an optimistic check only. Does not guarantee that all
|
||
|
|
weakly referenced receivers are still alive. See
|
||
|
|
:meth:`receivers_for` for a stronger search.
|
||
|
|
|
||
|
|
"""
|
||
|
|
if not self.receivers:
|
||
|
|
return False
|
||
|
|
if self._by_sender[ANY_ID]:
|
||
|
|
return True
|
||
|
|
if sender is ANY:
|
||
|
|
return False
|
||
|
|
return hashable_identity(sender) in self._by_sender
|
||
|
|
|
||
|
|
def receivers_for(self, sender):
|
||
|
|
"""Iterate all live receivers listening for *sender*."""
|
||
|
|
# TODO: test receivers_for(ANY)
|
||
|
|
if self.receivers:
|
||
|
|
sender_id = hashable_identity(sender)
|
||
|
|
if sender_id in self._by_sender:
|
||
|
|
ids = (self._by_sender[ANY_ID] |
|
||
|
|
self._by_sender[sender_id])
|
||
|
|
else:
|
||
|
|
ids = self._by_sender[ANY_ID].copy()
|
||
|
|
for receiver_id in ids:
|
||
|
|
receiver = self.receivers.get(receiver_id)
|
||
|
|
if receiver is None:
|
||
|
|
continue
|
||
|
|
if isinstance(receiver, WeakTypes):
|
||
|
|
strong = receiver()
|
||
|
|
if strong is None:
|
||
|
|
self._disconnect(receiver_id, ANY_ID)
|
||
|
|
continue
|
||
|
|
receiver = strong
|
||
|
|
yield receiver
|
||
|
|
|
||
|
|
def disconnect(self, receiver, sender=ANY):
|
||
|
|
"""Disconnect *receiver* from this signal's events.
|
||
|
|
|
||
|
|
:param receiver: a previously :meth:`connected<connect>` callable
|
||
|
|
|
||
|
|
:param sender: a specific sender to disconnect from, or :obj:`ANY`
|
||
|
|
to disconnect from all senders. Defaults to ``ANY``.
|
||
|
|
|
||
|
|
"""
|
||
|
|
if sender is ANY:
|
||
|
|
sender_id = ANY_ID
|
||
|
|
else:
|
||
|
|
sender_id = hashable_identity(sender)
|
||
|
|
receiver_id = hashable_identity(receiver)
|
||
|
|
self._disconnect(receiver_id, sender_id)
|
||
|
|
|
||
|
|
if ('receiver_disconnected' in self.__dict__ and
|
||
|
|
self.receiver_disconnected.receivers):
|
||
|
|
self.receiver_disconnected.send(self,
|
||
|
|
receiver=receiver,
|
||
|
|
sender=sender)
|
||
|
|
|
||
|
|
def _disconnect(self, receiver_id, sender_id):
|
||
|
|
if sender_id == ANY_ID:
|
||
|
|
if self._by_receiver.pop(receiver_id, False):
|
||
|
|
for bucket in self._by_sender.values():
|
||
|
|
bucket.discard(receiver_id)
|
||
|
|
self.receivers.pop(receiver_id, None)
|
||
|
|
else:
|
||
|
|
self._by_sender[sender_id].discard(receiver_id)
|
||
|
|
|
||
|
|
def _cleanup_receiver(self, receiver_ref):
|
||
|
|
"""Disconnect a receiver from all senders."""
|
||
|
|
self._disconnect(receiver_ref.receiver_id, ANY_ID)
|
||
|
|
|
||
|
|
def _cleanup_sender(self, sender_ref):
|
||
|
|
"""Disconnect all receivers from a sender."""
|
||
|
|
sender_id = sender_ref.sender_id
|
||
|
|
assert sender_id != ANY_ID
|
||
|
|
self._weak_senders.pop(sender_id, None)
|
||
|
|
for receiver_id in self._by_sender.pop(sender_id, ()):
|
||
|
|
self._by_receiver[receiver_id].discard(sender_id)
|
||
|
|
|
||
|
|
def _clear_state(self):
|
||
|
|
"""Throw away all signal state. Useful for unit tests."""
|
||
|
|
self._weak_senders.clear()
|
||
|
|
self.receivers.clear()
|
||
|
|
self._by_sender.clear()
|
||
|
|
self._by_receiver.clear()
|
||
|
|
|
||
|
|
|
||
|
|
receiver_connected = Signal("""\
|
||
|
|
Sent by a :class:`Signal` after a receiver connects.
|
||
|
|
|
||
|
|
:argument: the Signal that was connected to
|
||
|
|
:keyword receiver_arg: the connected receiver
|
||
|
|
:keyword sender_arg: the sender to connect to
|
||
|
|
:keyword weak_arg: true if the connection to receiver_arg is a weak reference
|
||
|
|
|
||
|
|
.. deprecated:: 1.2
|
||
|
|
|
||
|
|
As of 1.2, individual signals have their own private
|
||
|
|
:attr:`~Signal.receiver_connected` and
|
||
|
|
:attr:`~Signal.receiver_disconnected` signals with a slightly simplified
|
||
|
|
call signature. This global signal is planned to be removed in 1.6.
|
||
|
|
|
||
|
|
""")
|
||
|
|
|
||
|
|
|
||
|
|
class NamedSignal(Signal):
|
||
|
|
"""A named generic notification emitter."""
|
||
|
|
|
||
|
|
def __init__(self, name, doc=None):
|
||
|
|
Signal.__init__(self, doc)
|
||
|
|
|
||
|
|
#: The name of this signal.
|
||
|
|
self.name = name
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
base = Signal.__repr__(self)
|
||
|
|
return "%s; %r>" % (base[:-1], self.name)
|
||
|
|
|
||
|
|
|
||
|
|
class Namespace(dict):
|
||
|
|
"""A mapping of signal names to signals."""
|
||
|
|
|
||
|
|
def signal(self, name, doc=None):
|
||
|
|
"""Return the :class:`NamedSignal` *name*, creating it if required.
|
||
|
|
|
||
|
|
Repeated calls to this function will return the same signal object.
|
||
|
|
|
||
|
|
"""
|
||
|
|
try:
|
||
|
|
return self[name]
|
||
|
|
except KeyError:
|
||
|
|
return self.setdefault(name, NamedSignal(name, doc))
|
||
|
|
|
||
|
|
|
||
|
|
class WeakNamespace(WeakValueDictionary):
|
||
|
|
"""A weak mapping of signal names to signals.
|
||
|
|
|
||
|
|
Automatically cleans up unused Signals when the last reference goes out
|
||
|
|
of scope. This namespace implementation exists for a measure of legacy
|
||
|
|
compatibility with Blinker <= 1.2, and may be dropped in the future.
|
||
|
|
|
||
|
|
"""
|
||
|
|
|
||
|
|
def signal(self, name, doc=None):
|
||
|
|
"""Return the :class:`NamedSignal` *name*, creating it if required.
|
||
|
|
|
||
|
|
Repeated calls to this function will return the same signal object.
|
||
|
|
|
||
|
|
"""
|
||
|
|
try:
|
||
|
|
return self[name]
|
||
|
|
except KeyError:
|
||
|
|
return self.setdefault(name, NamedSignal(name, doc))
|
||
|
|
|
||
|
|
|
||
|
|
signal = Namespace().signal
|