matplotlib: How to pick up shift click on figure?

Question

I have a matplotlib and I have created a button_press_event like this:

self.fig.canvas.mpl_connect('button_press_event', self.onClick)

def onClick(self, event)
    if event.button == 1:
        # draw some artists on left click

    elif event.button == 2:
        # draw a vertical line on the mouse x location on wheel click

    elif event.button == 3:
        # clear artists on right click

Now is it possible to modify the wheel click handler to something like this

    elif event.button == 2 or (event.button == 1 and event.key == "shift"):
        # draw a vertical line on the mouse x location 
        # on wheel click or on shift+left click 
        # (alternative way if there is no wheel for example)

It seems that button_press_event doesn't support keys and key_press_event doesn't support mouse button clicks, but I'm not sure.

Is there a way?

Rend

Answer 1

You can also bind a key press and key release events and do something like:

self.fig.canvas.mpl_connect('key_press_event', self.on_key_press)
self.fig.canvas.mpl_connect('key_release_event', self.on_key_release)

...

def on_key_press(self, event):
   if event.key == 'shift':
       self.shift_is_held = True

def on_key_release(self, event):
   if event.key == 'shift':
       self.shift_is_held = False

Then you can check in your onClick function if self.shift_is_held.

if event.button == 3:
    if self.shift_is_held:
        do_something()
    else:
        do_something_else()

Merger

Seems like a good idea and workaround until a proper support for modifier keys with mouse buttons is implemented. Thanks Viktor! – Rend

FYI, you could use event.key == 'shift+left' to capture shift + left keyboard buttons – Meletius

I like this answer, but I think it has issues when multiple keys are pressed, since key_release_event doesn't say which key is released. E.g., consider: 1. press shift (key_press_event, key='shift') 2. press ctrl (key_press_event, key='ctrl+shift') 3. release shift (key_release_event, key='ctrl+shift') 4. release ctrl (key_release_event, key='ctrl') At the end, no keys are held but shift_is_held==True. You might change the conditionals to if 'shift' in event.key, but then if you release ctrl first shift is still held and yet shift_is_held==False... Any ideas? – Gluteal

Answer 2

If you are on Qt then you can simply use:

def onClick(self, event)
    # queries the pressed modifier keys
    mods = QGuiApplication.queryKeyboardModifiers()
    if event.button == 1 and mods == Qt.ShiftModifier:
        # do something when shift-clicking

Warfarin