class_docstr: Represents a mouse event that occurred on a SceneCanvas. This event is
  delivered to all entities whose mouse interaction area is under the event.
docstr: The mouse press event that initiated a mouse drag, if any.
docstr_tok: ["The","mouse","press","event","that","initiated","a","mouse","drag",",","if","any","."]
code: def press_event(self):
      """The mouse press event that initiated a mouse drag, if any."""
      if self.mouse_event.press_event is None:
          return None
      ev = self.copy()
      ev.mouse_event = self.mouse_event.press_event
      return ev
  
file_path: vispy/vispy/scene/events.py
imports: from __future__ import division
  from ..util.event import Event
label_desc: Use image node_id 6 for calling the SceneMouseEvent obj's underlying member method code with example usage: obj.press_event() and returns: ev, None