Tkinter setting alpha

[Jonathan Hayward]

I'm trying to make a Tkinter/Python port of the demo at http://wiki.tcl.tk/10515
, which has adjustable alpha under Windows and (I think) MacOS.

I'm not quite sure how to port:

    wm attributes . -alpha [expr {$alphaLevel + 0.05} ]
    set AlphaLevel [wm attributes . -alpha]

The goal is to have a screen pop that fades in and out at least on
Windows, and it would be nice if it could fade on other platforms
(including my preferred Linux).

Two questions:

1: Is Tkinter a good choice, or are there other libraries that are
easier and/or will allow cross-platform GUI work with (ideally) fading
in and out?

2: If I go with Tkinter, how can I port lines like those quoted above
to be able to get and set a Frame's alpha value?

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