Why does the tkinter progress bar makes things so much slower?

Question

Hello,

I have the following code for extracting a tar.gz file whilst keeping tabs on the progress:

from __future__ import division
import tarfile
import os

theArchive = "/Users/Dennis/Instances/atlassian-jira-enterprise-4.1.2-standalone.tar.gz"

a = tarfile.open(theArchive)

tarsize = 0

print "Computing total size"
for tarinfo in a:
    tarsize = tarsize + tarinfo.size

realz = tarsize
print "compressed size: " + str(a.fileobj.size)
print "uncompressed size: " + str(tarsize)

tarsize = 0

for tarinfo in a:
    print tarinfo.name, "is", tarinfo.size, "bytes in size and is",
    if tarinfo.isreg():
        print "a regular file."
    elif tarinfo.isdir():
        print "a directory."
    else:
        print "something else."
    a.extract(tarinfo)
    tarsize = tarsize + tarinfo.size
    print str(tarsize) + "/" + str(realz)
    outout = tarsize / realz
    print "progress: " + str(outout)

a.close()

This is quite speedy and extracts a 100MB tar.gz in 10 secs. I wanted to have this visually as well so I changed this to include a tkinter progress bar:

from __future__ import division
import tarfile
import os
import Tkinter

class Meter(Tkinter.Frame):
    def __init__(self, master, width=300, height=20, bg='white', fillcolor='orchid1',\
                 value=0.0, text=None, font=None, textcolor='black', *args, **kw):
        Tkinter.Frame.__init__(self, master, bg=bg, width=width, height=height, *args, **kw)
        self._value = value

        self._canv = Tkinter.Canvas(self, bg=self['bg'], width=self['width'], height=self['height'],\
                                    highlightthickness=0, relief='flat', bd=0)
        self._canv.pack(fill='both', expand=1)
        self._rect = self._canv.create_rectangle(0, 0, 0, self._canv.winfo_reqheight(), fill=fillcolor,\
                                                 width=0)
        self._text = self._canv.create_text(self._canv.winfo_reqwidth()/2, self._canv.winfo_reqheight()/2,\
                                            text='', fill=textcolor)
        if font:
            self._canv.itemconfigure(self._text, font=font)

        self.set(value, text)
        self.bind('<Configure>', self._update_coords)

    def _update_coords(self, event):
        '''Updates the position of the text and rectangle inside the canvas when the size of
        the widget gets changed.'''
        # looks like we have to call update_idletasks() twice to make sure
        # to get the results we expect
        self._canv.update_idletasks()
        self._canv.coords(self._text, self._canv.winfo_width()/2, self._canv.winfo_height()/2)
        self._canv.coords(self._rect, 0, 0, self._canv.winfo_width()*self._value, self._canv.winfo_height())
        self._canv.update_idletasks()

    def get(self):
        return self._value, self._canv.itemcget(self._text, 'text')

    def set(self, value=0.0, text=None):
        #make the value failsafe:
        if value < 0.0:
            value = 0.0
        elif value > 1.0:
            value = 1.0
        self._value = value
        if text == None:
            #if no text is specified use the default percentage string:
            text = "Extraction: " + str(int(round(100 * value))) + ' %'
        self._canv.coords(self._rect, 0, 0, self._canv.winfo_width()*value, self._canv.winfo_height())
        self._canv.itemconfigure(self._text, text=text)
        self._canv.update_idletasks()

##-------------demo code--------------------------------------------##

def _goExtract(meter, value):
    meter.set(value)
    if value < 1.0:
        value = value + 0.005
        meter.after(50, lambda: _demo(meter, value))
    else:
        meter.set(value, 'Demo successfully finished')

if __name__ == '__main__':
    root = Tkinter.Tk(className='meter demo')
    m = Meter(root, relief='ridge', bd=3)
    m.pack(fill='x')
    m.set(0.0, 'Computing file size...')
    m.after(1000)

    theArchive = "/Users/Dennis/Instances/atlassian-jira-enterprise-4.1.2-standalone.tar.gz"

    a = tarfile.open(theArchive)

    tarsize = 0

    for tarinfo in a:
        tarsize = tarsize + tarinfo.size

    realz = tarsize
    print "real size: " + str(tarsize)
    print "compressed size: " + str(a.fileobj.size)

    m.set(0.0, 'Done computing!')
    m.after(1000)

    tarsize = 0

    for tarinfo in a:
        print tarinfo.name, "is", tarinfo.size, "bytes in size and is",
        if tarinfo.isreg():
            print "a regular file."
        elif tarinfo.isdir():
            print "a directory."
        else:
            print "something else."
        a.extract(tarinfo)
        tarsize = tarsize + tarinfo.size
        print str(tarsize) + "/" + str(realz)
        outout = tarsize / realz
        m.set(outout)
        print "progress: " + str(outout)

    a.close()

    m.set(1.0, 'Extraction complete!')
    m.after(1000)
    m.after(1000, lambda: _goExtract(m, 0.0))

It works all fine and dandy but the process now takes more than 2 minutes. Why does this happen and how can I fix this?

Thanks!

Dennis

Answer 1

How big are the files in your archive? You are almost certainly updating the progress bar a lot more than you need to -- it's common to include a check in your set() function so that it just returns without updating if the change from the last value is too small. With a 300px canvas there's definitely no point in updating for a change of less than 0.3% and probably not much point in updating more often than every 1%.

As your process usually finishes in 10s, you may want to introduce a time-based check too, as even updating every 1% will be 10 times per second, which is more than you need. It would be interesting to see how long Tk takes to draw the bar if you drive it from a simple for loop.