napari.utils.events.EmitterGroup#

class napari.utils.events.EmitterGroup(source: Any | None = None, auto_connect: bool = False, **emitters: type[Event] | EventEmitter | None)[source]#

Bases: EventEmitter

EmitterGroup instances manage a set of related EventEmitters. Its primary purpose is to provide organization for objects that make use of multiple emitters and to reduce the boilerplate code needed to initialize those emitters with default connections.

EmitterGroup instances are usually stored as an ‘events’ attribute on objects that use multiple emitters. For example:

 EmitterGroup  EventEmitter
         |       |
Canvas.events.mouse_press
Canvas.events.resized
Canvas.events.key_press

EmitterGroup is also a subclass of EventEmitters, allowing it to emit its own events. Any callback that connects directly to the EmitterGroup will receive all of the events generated by the group’s emitters.

Parameters:
  • source (object) – The object that the generated events apply to.

  • auto_connect (bool) – If auto_connect is True, then one connection will be made for each emitter that looks like emitter.connect((source, 'on_' + event_name)). This provides a simple mechanism for automatically connecting a large group of emitters to default callbacks. By default, false.

  • emitters – See the add method.

Methods

add([auto_connect])

Add one or more EventEmitter instances to this emitter group. Each keyword argument may be specified as either an EventEmitter instance or an Event subclass, in which case an EventEmitter will be generated automatically::.

block([callback])

Block this emitter.

block_all()

Block all emitters in this group by increase counter of semaphores for each event emitter

blocked([callback])

Return boolean indicating whether the emitter is blocked for the given callback.

blocker([callback])

Return an EventBlocker to be used in 'with' statements

blocker_all()

Return an EventBlockerAll to be used in 'with' statements

connect(callback[, ref, position, before, after])

Connect the callback to the event group.

disconnect([callback])

Disconnect the callback from this group.

unblock([callback])

Unblock this emitter.

unblock_all()

Unblock all emitters in this group, by decrease counter of semaphores for each event emitter.

Attributes

callback_refs

The set of callback references

callbacks

The set of callbacks

emitters

List of current emitters in this group.

ignore_callback_errors

Whether exceptions during callbacks will be caught by the emitter

print_callback_errors

Print a message and stack trace if a callback raises an exception

source

The object that events generated by this emitter apply to

Details

add(auto_connect: bool | None = None, **kwargs: type[Event] | EventEmitter | None)[source]#

Add one or more EventEmitter instances to this emitter group. Each keyword argument may be specified as either an EventEmitter instance or an Event subclass, in which case an EventEmitter will be generated automatically:

# This statement:
group.add(mouse_press=MouseEvent,
          mouse_release=MouseEvent)

# ..is equivalent to this statement:
group.add(mouse_press=EventEmitter(group.source, 'mouse_press',
                                   MouseEvent),
          mouse_release=EventEmitter(group.source, 'mouse_press',
                                     MouseEvent))
block_all()[source]#

Block all emitters in this group by increase counter of semaphores for each event emitter

blocker_all() EventBlockerAll[source]#

Return an EventBlockerAll to be used in ‘with’ statements

Notes

For example, one could do:

with emitter.blocker_all():
    pass  # ..do stuff; no events will be emitted..
connect(callback: Callable[[Event], None] | Callable[[], None] | tuple[weakref.ReferenceType[Any], str] | EventEmitter | EmitterGroup, ref: bool | str = False, position: Literal['first', 'last'] = 'first', before: str | Callable[[Event], None] | Callable[[], None] | list[str | Callable[[Event], None] | Callable[[], None]] | None = None, after: str | Callable[[Event], None] | Callable[[], None] | list[str | Callable[[Event], None] | Callable[[], None]] | None = None)[source]#

Connect the callback to the event group. The callback will receive events from all of the emitters in the group.

See EventEmitter.connect() for arguments.

disconnect(callback: Callable[[Event], None] | Callable[[], None] | None = None)[source]#

Disconnect the callback from this group. See connect() and EventEmitter.connect() for more information.

property emitters: dict[str, EventEmitter]#

List of current emitters in this group.

property ignore_callback_errors#

Whether exceptions during callbacks will be caught by the emitter

This allows it to continue invoking other callbacks if an error occurs.

unblock_all()[source]#

Unblock all emitters in this group, by decrease counter of semaphores for each event emitter. if block is called twice and unblock is called once, then events will be still blocked. See Semaphore (programming).