'Decides if the Ctrl+Shift is pressed, in which case returns True.
If Ctrl+Shift+C or Ctrl+Shift+V are pressed, copies or pastes,
acordingly. Return necesary so it doesn\'t perform other action,
like killing the process on Ctrl+C.
Note that it won\'t care about order: Shift+Ctrl+V will work just as
Ctrl+Shift+V.'

def copy_or_paste(self, widget, event):

    control_key = 'control-mask'
    shift_key = 'shift-mask'
    last_pressed_key = Gdk.keyval_name(event.get_keyval()[1])
    set_pressed_special_keys = set(event.state.value_nicks)
    if (event.type == Gdk.EventType.KEY_PRESS):
        if ({control_key, shift_key} <= set_pressed_special_keys):
            if (last_pressed_key == 'C'):
                self.copy_clipboard()
            elif (last_pressed_key == 'V'):
                self.paste_clipboard()
            return True
