Previously I set up a toggle routine in the branch to toggle a led, but it never did, so I stripped things down to just the simple 'print' statement... but nothing has ever shown on the browser screen.
I've tried using different branch names and print msgs and crossing my fingers etc, but still never had any sign that a button press has ever reaches the branch.
If I could have got it working without bothering you I would have, but after many hours of trying everything I could think of, I have to conclude that the interupt function appears not to work (I hope I'm wrong), which is something I thought you'd want to know about and check out for yourself.
Footnote - The one thing I'm not sure about is the pin designations.
I've been using just the number 0 for gpio00 and 16 for gpio16 etc, but I've seen previous articles that stipulate eg: D3 ... I'm sure I found out ages ago that eg: D3 doesn't correspond to gpio03, but there's still that element of uncertainty about what/why the use of the 'D' prefix.