Have attached uitabs.py.  From the header comments:

Standalone 'tabs' widget to switch between multiple different views.

Unlike the Tkinter ttk.Notebook widget, this widget is suitable for
displaying a potentially large number of tabs, as might be found in a
tabbed editor. If there are too many tabs to show based on the available
width, the remainder can be viewed via a popup menu on the last tab.

Tabs can be rearranged by dragging, closed, or new tabs added. Each tab
can have a title which is displayed in the tab, a tooltip for when the
mouse hovers over the tab, and a 'dirty' indicator that can be used to
indicate files needing to be saved.

The appearance and behaviour of the tabs is strongly influenced by the
TextMate editor on Mac OS X.

Implementation is via a single Tkinter canvas.

Unlike many other tabbed widgets, this widget does not take care of
actually switching content being displayed; this is left to the caller.

A UITabsObserver (see below) must be provided to the widget, and is
used to notify the caller when changes are made that must be reflected
in other parts of the user interface.