I tried to test this locally, but that lead me to discovering that this dialog in broken on Fedora 37 with py311 with tk 8.6.12 with wayland both on this branch and 3.6.2 and with the system Python + building from the py311 branch. I have not chased down which of those is the source of the problem (but if I had to guess I would say wayland....)

This may catch out some people who type in the extension they want without changing the selector? Is that actually true and if so, do we think that is going to be a common problem? We probably should mention it as a behavior change?

I tried to test this locally, but that lead me to discovering that this dialog in broken on Fedora 37 with py311 with tk 8.6.12 with wayland both on this branch and 3.6.2 and with the system Python + building from the py311 branch. I have not chased down which of those is the source of the problem (but if I had to guess I would say wayland....)

I don't see any such problem with RPM Matplotlib or main; and I'm not sure what py311 branch you mean.

This may catch out some people who type in the extension they want without changing the selector? Is that actually true and if so, do we think that is going to be a common problem? We probably should mention it as a behavior change?

I hadn't considered that - I copied the behaviour from the GTK backend, which uses the selected format, but it looks like macosx and Qt ignore the selected format and just use the filename, and wx uses the selected format but warns if it differs from the filename. I'm not sure which behaviour is most intuitive - even on default Windows programs, turns out mspaint uses the selected format, while wordpad uses the filename.

by py311, I mean the v3.11 branch from CPython. If Elliott can not reproduce this I'll assume this is a local problem....

OK, I can reproduce in ipython when calling plt.ion(). However, this is broken with Fedora Python 3.11 on Wayland, and conda Python 3.8 on X11, so it's unrelated to either of those, and also unrelated to this PR.

Wx warning is my favorite behavior (it tells the user they are doing something ambiguous and we have taken a guess at what they meant), all of the backends should probably do that.

As for which way it breaks:

• the case for making them all the same (no matter which way) is about consistency (which may catch someone out when they change backends), the case against is that it is going to change behavior and probably catch someone out
• the case for leaving them all as they are the opposite

As for which way makes more sense:

• if you follow the format, then the user can drop writing the extension into the text box and we treat format as prescriptive that happens to filter the UI
• if you follow the filename, then we do what the user asked for and the format in the UI is "just" a file filter.

FWIW I much prefer following whatever the user typed (which is qt's behavior); as an example, inkscape forces you (or at least used to, haven't checked recently) to go through the combobox which I find supremely annoying (especially when there are many, many formats supported and you need to figure out where is the one you want).

I pushed this to 3.8 because we need to sort out which of the 3 behaviors is "right".

Having spoken to some others and looked at how different software behaves, I now also think it's best to have the typed extension take priority over the dropdown, so keeping the existing behaviour. I've updated the PR, so now it only uses the dropdown selection if the filename contains no extension, and also correctly sorts the extensions in alphabetical order.

ping @anntzer @tacaswell for new behaviour change.

👍🏻 to this change, but I think it needs a behavior change note.

Ditto, the new behavior looks good to me.

@daniilS can you handle the behaviour change? Otherwise this looks good to go...

@jklymak apologies for the delay, behaviour change note added & api note updated to 3.8

Also, the default file name includes .png, which means you can't simply change the type and get a different type, as the filename overrides. If would be nice if (extension of text == old filetype) then the extension were changed to the new type. Or perhaps the extension could just not be added.

Good point - Windows (and I think MacOS, but not sure) automatically edits the filename when changing the dropdown selection, but the Tk implementation of the dialog on Linux does not. Not giving an extension by default seems like the best solution to me.