class_docstr: Two dimentional raster of callbacks for mouse events.
code: def __init__(self):
      def dummy_callback(cli, mouse_event):
          """
          :param mouse_event: `MouseEvent` instance.
          """
  
      # Map (x,y) tuples to handlers.
      self.mouse_handlers = defaultdict(lambda: dummy_callback)
  
imports: from __future__ import unicode_literals
  from itertools import product
  from collections import defaultdict
label_desc: Use image node_id 1 to create a new MouseHandlers object from inherited base classes: object with example: obj = MouseHandlers()