:mod:`!tkinter.dnd` --- Drag and drop support

.. module:: tkinter.dnd
   :synopsis: Tkinter drag-and-drop interface

Source code: :source:`Lib/tkinter/dnd.py`

The :mod:`!tkinter.dnd` module provides drag-and-drop support for objects within a single application, within the same window or between windows. To enable an object to be dragged, you must create an event binding for it that starts the drag-and-drop process. Typically, you bind a ButtonPress event to a callback function that you write (see :ref:`Bindings-and-Events`). The function should call :func:`dnd_start`, where source is the object to be dragged, and event is the event that invoked the call (the argument to your callback function).

Selection of a target object occurs as follows:

1. Top-down search of the area under the mouse for a target widget:
   • the target widget should have a callable dnd_accept attribute;
   • if dnd_accept is not present or returns None, the search moves to the parent widget;
   • if no target widget is found, the target object is None.
2. Call to <old_target>.dnd_leave(source, event).
3. Call to <new_target>.dnd_enter(source, event).
4. Call to <target>.dnd_commit(source, event) to notify of the drop.
5. Call to <source>.dnd_end(target, event) to signal the end of drag-and-drop.

The DndHandler class handles drag-and-drop events tracking Motion and ButtonRelease events on the root of the event widget.

.. method:: cancel(event=None)
   Cancel the drag-and-drop process.

.. method:: finish(event, commit=0)
   Execute end of drag-and-drop functions.

.. method:: on_motion(event)
   Inspect area below mouse for target objects while a drag
   is performed.

.. method:: on_release(event)
   Signal end of drag when the release pattern is triggered.

.. function:: dnd_start(source, event)
   Factory function for the drag-and-drop process.
   Return the :class:`DndHandler` instance managing the drag, or ``None`` if a
   drag could not be started.

.. seealso::
   :ref:`Bindings-and-Events`