Sunday, July 24, 2016

TKinter, ttk, and Progressbar

tl;dr: ttk.Progressbar is max 99 by default, not 100, despite the documentation. If you try to overfill it, it won't accept the call that does so.

I was building a front end for a scraper app, and at first I tried Xcode and the Interface Builder (which I first saw over two decades ago on a NeXT machine, it was glorious then and it still is), but I couldn't get it to mesh with my Python code (so much of the online help is out of date). A friend told me I was being an idiot and should try something simpler, and I settled on TKinter, which had me up and running in very little time. (The front end took only two days, but I wasn't committing every waking hour to it, and I had to figure out how to take my linear Python script and conceive of it in the looping GUI manner, which was difficult.)

I wanted a text box field so the scraper could print to it like it does with Python's print statement to the terminal (but I don't want the user to have to deal with the terminal or the console). I ended up using ScrolledText, which you have to import (well as far as I can tell, and it's working, so, once it works, I don't have time to poke at it too much). (NB: with ScrolledText, I needed setgrid=True to make the frames resize nicely, this was VITAL, packing frames in TKinter is an art I do not yet understand, and with the ScrolledText field, you might want state='normal' to print to it, then state='disabled' so the user doesn't type in it [but loses copy capability], you'll want insert(END, new_string) to print at the bottom of your field, but then you also need see(END) so that it scrolls to the bottom -- otherwise it prints on the bottom but the view stays put at the top. Details.)

Then I wanted two progress bars, one to show the user the scrape progress and the second to show the parsing progress. The scraping one I needed to fudge a little, so I tried....

my_window.scrape_progress.step(10) # first init step
my_window.scrape_progress.step(20) # bigger step

my_window.scrape_progress.step(20) # another bigger step
my_window.scrape_progress.step(50) # jump to done!

Where scrape_progress is the name of the Progressbar object for my scraping progress.

As you can see, that's 10 + 20 + 20 + 50 = 100.

The bar would fill 10% (10), then to about 30% (10+20), then to about 50% (10+20+20), then it wouldn't fill anymore.

Eventually out of annoyance when trying alternatives, instead of 50 in the last step I used 49, and it worked.

So no, the max is not 100, it's 99, so the bar values are probably 0-99 for 100 increments, as 0-100 would be 101 increments. I suspect that step(100) won't work, but step(99) should fill it to 100%.

Some code:

from Tkinter import *
from ttk import * # ttk widgets should overwrite Tkinter ones in the namespace.
import ScrolledText as tkst  # Not sure why this is its own library.

# from my window class def, nothing to do with the Progressbar:
def print_to_text_field(self, the_string): 
new_string = '\n' + the_string
self.the_text_field.insert(END, new_string)