Question

I’m trying to write a simple gui-based application in pygtk which provides ‘live’ previewing of text-based markup. The markup processing, however, can be quite computationally expensive and slow to run, so updating the preview on every keystroke is not really viable. Instead I’d like to have the update run only when user input lapses. Ideally, I’d have it update a specified interval after the last keystroke in a sequence.

I’ve looked into using threading.Timer, by cancelling and re-starting a timer to invoke the update function each time the “changed” signal is emitted. I’ve also tried to use gtk.idle_add(), but I can’t seem to get it working.

Below is a very simple example – could someone suggest the best strategy to achieve what I’m after, preferably with an example?

import gtk

class example:
    def __init__(self):
        window = gtk.Window()
        window.set_title("example")
        window.resize(600,400)
        box = gtk.HBox(homogeneous = True, spacing = 2)
        buf = gtk.TextBuffer()
        buf.connect("changed", self.buf_on_change)
        textInput = gtk.TextView(buf)
        box.add(textInput)
        self.lbl = gtk.Label()
        box.add(self.lbl)
        window.add(box)
        window.connect("destroy", gtk.main_quit)
        window.show_all()

    def buf_on_change(self, buf):
        txt = buf.get_text(*buf.get_bounds())
        output = self.renderText(txt)
        self.lbl.set_text(output)

    def renderText(self, txt):
        # perform computation-intensive text-manipulation here
        output = txt
        return output

if __name__ == '__main__':
    example()
    gtk.main()

Answer 1

so I think I found a solution using glib.timeout_add() instead of threading.Timer:

import gtk, glib

class example:
    def __init__(self):
        window = gtk.Window()
        window.set_title("example")
        window.resize(600,400)
        box = gtk.HBox(homogeneous = True, spacing = 2)
        self.buf = gtk.TextBuffer()
        self.buf.connect("changed", self.buf_on_change)
        textInput = gtk.TextView(self.buf)
        box.add(textInput)
        self.lbl = gtk.Label()
        box.add(self.lbl)
        window.add(box)
        window.connect("destroy", gtk.main_quit)
        window.show_all()

        self.timer = glib.timeout_add(1000, self.renderText)

    def buf_on_change(self, buf):
        glib.source_remove(self.timer)
        self.timer = glib.timeout_add(1000, self.renderText)


    def renderText(self):
        txt = self.buf.get_text(*self.buf.get_bounds())
        # perform computation-intensive text-manipulation here
        self.lbl.set_text(txt)
        return False

if __name__ == '__main__':
    example()
    gtk.main()

this seems to work as desired, but since I’m completely new to gtk (and desktop dui programming in general – in case you couldn’t tell 😉 ) I’d like to leave this question open in the hope that someone more experience might comment on the best way to achieve this kind of effect. I hope that’s okay?