为什么tkinter进度条会这么慢？

Question

我有一段代码，用来提取tar.gz文件，同时还能显示进度：

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()

这个过程挺快的，提取一个100MB的tar.gz文件只需要10秒。我想让这个过程在视觉上也能看到进度，所以我把代码改成了包含一个tkinter进度条：

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))

这样做一切都很好，但现在这个过程却需要超过2分钟。为什么会这样，我该怎么解决呢？

谢谢！

丹尼斯

Answer 1

你的档案文件有多大？你很可能在更新进度条时比实际需要的频率要高得多——通常在你的 set() 函数里加一个检查是个好主意，这样如果上一个值和当前值的变化太小，就直接返回，不进行更新。对于一个300像素的画布来说，如果变化小于0.3%，就没必要更新进度条，而且每次更新频率超过1%也没什么意义。

因为你的处理过程通常在10秒内完成，你可能还想加入一个基于时间的检查，因为即使是每1%更新一次，实际上也是每秒更新10次，这样频率就太高了。用一个简单的 for 循环来驱动进度条，看看Tk绘制这个条需要多长时间，应该会很有趣。