Shallow Thoughts : tags : tkinter

Unit Testing TkInter Apps

I've been making a lot of tweaks lately to MetaPho, in particular its Python/TkInter based replacement for my C/GTK2 image viewer Pho.

Pho has always had quite a few modes: it can be fullscreen, in a window sized for the current image, or in a fixed-size window; images can be scaled to the window/screen size, or you can zoom in/out, or you can view them at full size (pixel for pixel). It's fairly common that when I fix a bug in one mode, it introduces a new bug in a different mode because of the way the scaling code works.

Ideally, in a complicated program, you guard against problems like that with automated tests. But that's hard to do in a GUI (graphical user interface) app. A window comes up, but how do you make it do different things? How do you check whether it's showing the right thing, or if it's the right size?

I've tried a couple times to find hints on how to unit test Python scripts in either Tk or GTK, but there's not much help available. I think most people just give up and don't test their GUIs — just as I've always given up.

This time, I decided to really dive in and see if I could write a TkInter unit test script for testing all those different TkPho modes. It wasn't easy, but now I have a basic framework that I should be able to use for other GUI apps as well.

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Tags: python, tkinter, programming
[ 13:55 May 08, 2026    More programming | permalink to this entry | ]

Egg Timer in Python and TkInter

I left the water on too long in the garden again. I keep doing that: I'll set up something where I need to check back in five minutes or fifteen minutes, then I get involved in what I'm doing and 45 minutes later, the cornbread is burnt or the garden is flooded.

When I was growing up, my mom had a little mechanical egg timer. You twist the dial to 5 minutes or whatever, and it goes tick-tick-tick and then DING! I could probably find one of those to buy (they're probably all digital now and include clocks and USB plugs and bluetooth ports) but since the problem is always that I'm getting distracted by something on the computer, why not run an app there?

Of course, you can do this with shell commands. The simple solution is:

(sleep 300; zenity --info --text="Turn off the water!") &

But the zenity dialogs are small -- what if I don't notice it? -- and besides, I have to multiply by 60 to turn a minute delay into sleep seconds. I'm lazy -- I want the computer to do that for me!
Update: Ed Davies points out that "sleep 5m" also works.

A slightly more elaborate solution is at. Say something like: at now + 15 minutes and when it prompts for commands, type something like:

export DISPLAY=:0.0
zenity --info --text="Your cornbread is ready"

to pop up a window with a message. But that's too much typing and has the same problem of the small easily-ignored dialogs. I'd really rather have a great big red window that I can't possibly miss.

Surely, I thought, someone has already written a nice egg-timer application! I tried aptitude search timer and found several apps such as gtimer, which is much more complicated than I wanted (you can define named events and choose from a list of ... never mind, I stopped reading there). I tried googling, but didn't have much luck there either (lots of Windows and web apps, no Linux apps or cross-platform scripts).

Clearly just writing the damn thing was going to be easier than finding one. (Why is it that every time I want to do something simple on a computer, I have to write it? I feel so sorry for people who don't program.)

I wanted to do it in python, but what to use for the window that pops up? I've used python-gtk in the past, but I've been meaning to check out TkInter (the gui toolkit that's kinda-sorta part of Python) and this seemed like a nice opportunity since the goal was so simple.

The resulting script: eggtimer. Call it like this:

eggtimer 5 Turn off the water

and in five minutes, it will pop up a huge red window the size of the screen with your message in big letters. (Click it or hit a key to dismiss it.)

First Impressions of TkInter

It was good to have an excuse to try TkInter and compare it with python-gtk. TkInter has been recommended as something normally installed with Python, so the user doesn't have to install anything extra. This is apparently true on Windows (and maybe on Mac), but on Ubuntu it goes the other way: I already had pygtk, because GIMP uses it, but to use TkInter I had to install python-tk.

For developing I found TkInter irritating. Most of the irritation concerned the poor documentation: there are several tutorials demonstrating very basic uses, but not much detailed documentation for answering questions like "What class is the root Tk() window and what methods does it have?" (The best I found -- which never showed up in google, but was referenced from O'Reilly's Programming Python -- was here.) In contrast, python-gtk is very well documented.

Things I couldn't do (or, at least, couldn't figure out how to do, and googling found only postings from other people wanting to do the same thing):

• Button didn't respond to any of the obvious keys, like Return or Space, and in fact setting key handlers on the button didn't work -- I ended up setting a key handler on the root window.
• I couldn't find a way to set the root window size and background explicitly, so I had to set approximate window size by guessing at the size of the internal padding of the button.
• There's an alternate to the root Tk() window called Toplevel, which is documented and does allow setting window size. Unfortunately, it also pops up an empty dialog without being told to (presumably a bug).
• All of the tutorials I found for creating dialogs was wrong, and I finally gave up on dialogs and just used a regular window.
• I couldn't fork and return control to the shell, because TkInter windows don't work when called from a child process (for reasons no one seems to be able to explain), so you have to run it in the background with & if you want your shell prompt back.

I expect I'll be sticking with pygtk for future projects. It's just too hard figuring things out with no documentation. But it was fun having an excuse to try something new.

Tags: programming, python, tkinter
[ 14:35 Sep 04, 2007    More programming | permalink to this entry | ]