329 lines
13 KiB
Python
329 lines
13 KiB
Python
#!/usr/bin/python
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#
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# Urwid signal dispatching
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# Copyright (C) 2004-2012 Ian Ward
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#
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# Urwid web site: https://urwid.org/
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from __future__ import annotations
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import itertools
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import typing
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import warnings
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import weakref
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from collections.abc import Callable, Collection, Container, Iterable
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class MetaSignals(type):
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"""
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register the list of signals in the class variable signals,
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including signals in superclasses.
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"""
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def __init__(cls, name: str, bases: tuple[type, ...], d: dict[str, typing.Any]) -> None:
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signals = d.get("signals", [])
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for superclass in cls.__bases__:
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signals.extend(getattr(superclass, 'signals', []))
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signals = list({x: None for x in signals}.keys())
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d["signals"] = signals
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register_signal(cls, signals)
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super().__init__(name, bases, d)
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def setdefaultattr(obj, name, value):
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# like dict.setdefault() for object attributes
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if hasattr(obj, name):
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return getattr(obj, name)
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setattr(obj, name, value)
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return value
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class Key:
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"""
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Minimal class, whose only purpose is to produce objects with a
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unique hash
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"""
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__slots__ = ()
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class Signals:
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_signal_attr = '_urwid_signals' # attribute to attach to signal senders
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def __init__(self):
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self._supported = {}
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def register(self, sig_cls, signals: Container[str]) -> None:
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"""
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:param sig_class: the class of an object that will be sending signals
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:type sig_class: class
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:param signals: a list of signals that may be sent, typically each
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signal is represented by a string
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:type signals: signal names
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This function must be called for a class before connecting any
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signal callbacks or emitting any signals from that class' objects
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"""
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self._supported[sig_cls] = signals
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def connect(
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self,
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obj,
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name: str,
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callback: Callable[..., typing.Any],
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user_arg: typing.Any = None,
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*,
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weak_args: Iterable[typing.Any] = (),
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user_args: Iterable[typing.Any] = (),
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) -> Key:
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"""
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:param obj: the object sending a signal
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:type obj: object
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:param name: the signal to listen for, typically a string
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:type name: signal name
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:param callback: the function to call when that signal is sent
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:type callback: function
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:param user_arg: deprecated additional argument to callback (appended
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after the arguments passed when the signal is
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emitted). If None no arguments will be added.
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Don't use this argument, use user_args instead.
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:param weak_args: additional arguments passed to the callback
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(before any arguments passed when the signal
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is emitted and before any user_args).
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These arguments are stored as weak references
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(but converted back into their original value
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before passing them to callback) to prevent
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any objects referenced (indirectly) from
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weak_args from being kept alive just because
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they are referenced by this signal handler.
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Use this argument only as a keyword argument,
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since user_arg might be removed in the future.
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:type weak_args: iterable
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:param user_args: additional arguments to pass to the callback,
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(before any arguments passed when the signal
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is emitted but after any weak_args).
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Use this argument only as a keyword argument,
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since user_arg might be removed in the future.
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:type user_args: iterable
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When a matching signal is sent, callback will be called. The
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arguments it receives will be the user_args passed at connect
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time (as individual arguments) followed by all the positional
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parameters sent with the signal.
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As an example of using weak_args, consider the following snippet:
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>>> import urwid
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>>> debug = urwid.Text('')
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>>> def handler(widget, newtext):
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... debug.set_text("Edit widget changed to %s" % newtext)
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>>> edit = urwid.Edit('')
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>>> key = urwid.connect_signal(edit, 'change', handler)
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If you now build some interface using "edit" and "debug", the
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"debug" widget will show whatever you type in the "edit" widget.
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However, if you remove all references to the "debug" widget, it
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will still be kept alive by the signal handler. This because the
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signal handler is a closure that (implicitly) references the
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"edit" widget. If you want to allow the "debug" widget to be
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garbage collected, you can create a "fake" or "weak" closure
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(it's not really a closure, since it doesn't reference any
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outside variables, so it's just a dynamic function):
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>>> debug = urwid.Text('')
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>>> def handler(weak_debug, widget, newtext):
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... weak_debug.set_text("Edit widget changed to %s" % newtext)
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>>> edit = urwid.Edit('')
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>>> key = urwid.connect_signal(edit, 'change', handler, weak_args=[debug])
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Here the weak_debug parameter in print_debug is the value passed
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in the weak_args list to connect_signal. Note that the
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weak_debug value passed is not a weak reference anymore, the
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signals code transparently dereferences the weakref parameter
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before passing it to print_debug.
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Returns a key associated by this signal handler, which can be
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used to disconnect the signal later on using
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urwid.disconnect_signal_by_key. Alternatively, the signal
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handler can also be disconnected by calling
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urwid.disconnect_signal, which doesn't need this key.
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"""
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if user_arg is not None:
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warnings.warn(
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"Don't use user_arg argument, use user_args instead.",
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DeprecationWarning,
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)
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sig_cls = obj.__class__
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if name not in self._supported.get(sig_cls, ()):
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raise NameError(f"No such signal {name!r} for object {obj!r}")
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# Just generate an arbitrary (but unique) key
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key = Key()
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signals = setdefaultattr(obj, self._signal_attr, {})
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handlers = signals.setdefault(name, [])
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# Remove the signal handler when any of the weakref'd arguments
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# are garbage collected. Note that this means that the handlers
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# dictionary can be modified _at any time_, so it should never
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# be iterated directly (e.g. iterate only over .keys() and
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# .items(), never over .iterkeys(), .iteritems() or the object
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# itself).
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# We let the callback keep a weakref to the object as well, to
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# prevent a circular reference between the handler and the
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# object (via the weakrefs, which keep strong references to
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# their callbacks) from existing.
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obj_weak = weakref.ref(obj)
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def weakref_callback(weakref):
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o = obj_weak()
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if o:
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self.disconnect_by_key(o, name, key)
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user_args = self._prepare_user_args(weak_args, user_args, weakref_callback)
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handlers.append((key, callback, user_arg, user_args))
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return key
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def _prepare_user_args(
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self,
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weak_args: Iterable[typing.Any] = (),
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user_args: Iterable[typing.Any] = (),
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callback: Callable[..., typing.Any] | None = None,
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) -> tuple[Collection[weakref.ReferenceType], Collection[typing.Any]]:
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# Turn weak_args into weakrefs and prepend them to user_args
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w_args = tuple(weakref.ref(w_arg, callback) for w_arg in weak_args)
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args = tuple(user_args) or ()
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return (w_args, args)
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def disconnect(
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self,
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obj,
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name: str,
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callback: Callable[..., typing.Any],
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user_arg: typing.Any = None,
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*,
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weak_args: Iterable[typing.Any] = (),
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user_args: Iterable[typing.Any] = (),
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) -> None:
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"""
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:param obj: the object to disconnect the signal from
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:type obj: object
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:param name: the signal to disconnect, typically a string
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:type name: signal name
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:param callback: the callback function passed to connect_signal
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:type callback: function
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:param user_arg: the user_arg parameter passed to connect_signal
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:param weak_args: the weak_args parameter passed to connect_signal
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:param user_args: the weak_args parameter passed to connect_signal
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This function will remove a callback from the list connected
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to a signal with connect_signal(). The arguments passed should
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be exactly the same as those passed to connect_signal().
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If the callback is not connected or already disconnected, this
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function will simply do nothing.
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"""
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signals = setdefaultattr(obj, self._signal_attr, {})
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if name not in signals:
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return
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handlers = signals[name]
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# Do the same processing as in connect, so we can compare the
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# resulting tuple.
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user_args = self._prepare_user_args(weak_args, user_args)
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# Remove the given handler
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for h in handlers:
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if h[1:] == (callback, user_arg, user_args):
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return self.disconnect_by_key(obj, name, h[0])
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def disconnect_by_key(self, obj, name: str, key: Key) -> None:
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"""
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:param obj: the object to disconnect the signal from
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:type obj: object
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:param name: the signal to disconnect, typically a string
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:type name: signal name
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:param key: the key for this signal handler, as returned by
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connect_signal().
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:type key: Key
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This function will remove a callback from the list connected
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to a signal with connect_signal(). The key passed should be the
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value returned by connect_signal().
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If the callback is not connected or already disconnected, this
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function will simply do nothing.
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"""
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signals = setdefaultattr(obj, self._signal_attr, {})
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handlers = signals.get(name, [])
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handlers[:] = [h for h in handlers if h[0] is not key]
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def emit(self, obj, name: str, *args) -> bool:
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"""
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:param obj: the object sending a signal
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:type obj: object
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:param name: the signal to send, typically a string
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:type name: signal name
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:param args: zero or more positional arguments to pass to the signal callback functions
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This function calls each of the callbacks connected to this signal
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with the args arguments as positional parameters.
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This function returns True if any of the callbacks returned True.
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"""
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result = False
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signals = getattr(obj, self._signal_attr, {})
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handlers = signals.get(name, [])
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for key, callback, user_arg, (weak_args, user_args) in handlers:
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result |= self._call_callback(callback, user_arg, weak_args, user_args, args)
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return result
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def _call_callback(
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self,
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callback,
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user_arg: typing.Any,
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weak_args: Collection[weakref.ReferenceType],
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user_args: Collection[typing.Any],
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emit_args: Iterable[typing.Any],
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) -> bool:
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args_to_pass = []
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for w_arg in weak_args:
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real_arg = w_arg()
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if real_arg is not None:
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args_to_pass.append(real_arg)
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else:
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# de-referenced
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return False
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# The deprecated user_arg argument was added to the end
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# instead of the beginning.
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args = itertools.chain(args_to_pass, user_args, emit_args, (user_arg,) if user_arg is not None else ())
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return bool(callback(*args))
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_signals = Signals()
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emit_signal = _signals.emit
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register_signal = _signals.register
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connect_signal = _signals.connect
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disconnect_signal = _signals.disconnect
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disconnect_signal_by_key = _signals.disconnect_by_key
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