Event dispatchers

Custom event dispatcher class might be created to handle some matplotlib events just inheriting mpl_events.MplEventDispatcher class and implementing the required event handlers.

The following example shows how we can create the dispatcher for handling all mouse events:

from matplotlib import pyplot as plt
from mpl_events import MplEventDispatcher, mpl

class MouseEventDispatcher(MplEventDispatcher):

    def on_mouse_button_press(self, event: mpl.MouseEvent):
        print(f'mouse button {event.button} pressed')

    def on_mouse_button_release(self, event: mpl.MouseEvent):
        print(f'mouse button {event.button} released')

    def on_mouse_move(self, event: mpl.MouseEvent):
        print(f'mouse moved')

    def on_mouse_wheel_scroll(self, event: mpl.MouseEvent):
        print(f'mouse wheel scroll {event.step}')

figure = plt.figure()

# setup figure and make plots is here ...

mouse_dispatcher = MouseEventDispatcher(figure)

MplEventDispatcher class provides API (handler methods interface) for all matplotlib events. You may override and implement some of these methods for handling corresponding events.

The dispatcher might be connected to a canvas using mpl objects figure or axes (or canvas). In general, we do not need to think about it. We just pass figure instance to constructor usually. By default connection to events is made automatically. This behavior is controlled by connect argument.

And it is all. We do not need to worry about connecting/disconnecting or remember mpl event names.

If we want to use another methods (not MplEventDispatcher API) for handling events we can use mpl_events.mpl_event_handler() decorator inside our dispatcher class.

from mpl_events import MplEventDispatcher, MplEvent, mpl_event_handler, mpl

class CloseEventDispatcher(MplEventDispatcher):

    def _close_event_handler(self, event: mpl.CloseEvent):
        print(f'figure {event.canvas.figure} closing')

Also we can create event dispatchers hierarchies:

from mpl_events import MplEventDispatcher, mpl

class MyEventDispatcherBase(MplEventDispatcher):
    def on_figure_close(self, event: mpl.CloseEvent):
        print('figure closing from MyEventDispatcherBase')

class MyEventDispatcher(MyEventDispatcherBase):

    def on_figure_close(self, event: mpl.CloseEvent):
        print('figure closing from MyEventDispatcher')

    def on_figure_resize(self, event: mpl.ResizeEvent):
        print('figure resizing')

Event filters

Sometimes we need to look at, and possibly intercept, the events that are handled in dispatcher classes. We can use mpl_events.MplEventDispatcher.add_event_filter() method for adding an event filter callable that will intercept events.

event filter signature:

def event_filter(obj: MplEventDispatcher, event: mpl.Event) -> Optional[bool]:

The first argument if referecne to dispatcher object, the second argument is mpl event object. If the filter callable returns True, other filters and the handler for the event in the dispatcher class will not be called.

The example:

class Dispatcher(MplEventDispatcher):
    def on_key_press(self, event: mpl.KeyEvent):
        print('key press')

    def on_key_release(self, event: mpl.KeyEvent):
        print('key release')

def event_filter(obj: MplEventDispatcher, event: mpl.Event):
    if isinstance(obj, Dispatcher):
        if == MplEvent.KEY_PRESS.value:
            print('key press filtering')
            # No handling KEY_PRESS in "Dispatcher"
            return True

        elif == MplEvent.KEY_RELEASE.value:
            print('key release filtering')
            # Handling KEY_RELEASE in "Dispatcher" after filtering
            return False

dispatcher = Dispatcher(figure)

Event connections

The connection between event and handler incapsulated in mpl_events.MplEventConnection class. This class is high level wrapper for figure.canvas.mpl_connect/figure.canvas.mpl_disconnect mpl API.

MplEventConnection can be used if we want to handle events and do not use event dispatcher interface.

In this case we just create instance of MplEventConnection class and pass to constructor mpl object for connecting (figure, axes or canvas), event type as MplEvent enum and handler as callable. By default connection is made automatically. This behavior is controlled by connect argument.

from matplotlib import pyplot as plt
from mpl_events import MplEventConnection, MplEvent, mpl

def close_handler(event: mpl.CloseEvent):
    print('figure closing')

figure = plt.figure()

conn = MplEventConnection(figure, MplEvent.FIGURE_CLOSE, close_handler)

# MplEventConnection(event=<FIGURE_CLOSE:close_event>, handler=<function close_handler at 0x0000013FD1002E18>, id=5)

Also we can use the shortcut for MplEventConnection constuction using MplEvent.make_connection() method of MplEvent class:

from mpl_events import MplEvent

conn = MplEvent.FIGURE_CLOSE.make_connection(figure, close_handler)

Disable default key press event handler

Matplotlib figures usually contain navigation bar for some interactions with axes and this navigation bar handles key presses. By default key press handler is connected in FigureManagerBase mpl class. mpl-events provides disable_default_key_press_handler() function to disconnect the default key press handler. Also in event dispatcher classes we can use disable_default_handlers attribute.

Here is a simple example:

from matplotlib import pyplot as plt
from mpl_events import MplEventDispatcher, mpl

class KeyEventDispatcher(MplEventDispatcher):
    disable_default_handlers = True

    def on_key_press(self, event: mpl.KeyEvent):
        print(f'Pressed key {event.key}')

    def on_key_release(self, event: mpl.KeyEvent):
        print(f'Released key {event.key}')

figure = plt.figure()

dispatcher = KeyEventDispatcher(figure)