本文實例講述了Python顯示進度條的方法，是Python程序設計中非常實用的技巧。分享給大家供大家參考。具體方法如下：
首先，進度條和一般的print區(qū)別在哪里呢？
答案就是print會輸出一個/n，也就是換行符，這樣光標移動到了下一行行首，接著輸出，之前已經(jīng)通過stdout輸出的東西依舊保留，而且保證我們在下面看到最新的輸出結(jié)果。
進度條不然，我們必須再原地輸出才能保證他是一個進度條，否則換行了怎么還叫進度條？
最簡單的辦法就是，再輸出完畢后，把光標移動到行首，繼續(xù)在那里輸出更長的進度條即可實現(xiàn)，新的更長的進度條把舊的短覆蓋，就形成了動畫效果。
可以想到那個轉(zhuǎn)義符了吧，那就是/ r。
轉(zhuǎn)義符r就可以把光標移動到行首而不換行，轉(zhuǎn)義符n就把光標移動到行首并且換行。
在python中，輸出stdout(標準輸出)可以使用sys.stdout.write
例如：
Python
#!/usr/bin/env python# -*- coding=utf-8 -*-#Using GPL v2"""Usage:Just A Template"""from __future__ import division import sys,timej = '#'if __name__ == '__main__': for i in range(1,61): j += '#' sys.stdout.write(str(int((i/60)*100))+'% ||'+j+'->'+"/r") sys.stdout.flush() time.sleep(0.5)print
第二種思路是用轉(zhuǎn)義符/b
轉(zhuǎn)義符/b是退格鍵，也就是說把輸出的光標往回退格子，這樣就可以不用+=了，例如：
Python
#!/usr/bin/env python# -*- coding=utf-8 -*-#Using GPL v2"""Usage:Just A Template"""from __future__ import division import sys,timeif __name__ == '__main__': for i in range(1,61): sys.stdout.write('#'+'->'+"/b/b") sys.stdout.flush() time.sleep(0.5)print 光標回退2格，寫個#再回退，再寫，達到增長的目的了
不過寫這么多似乎是廢話，在耳邊常常聽到一句話：那就是不要重復造輪子。實際上python有豐富發(fā)lib幫你實現(xiàn)這個東西，你完全可以把心思放在邏輯開發(fā)上而不用注意這些小細節(jié)
下面要介紹的就是這個類“progressbar”(http://code.google.com/p/python-progressbar/)，使用easy_install可以方便的安裝這個類庫，其實就一個文件，拿過來放到文件同一個目錄下面也直接可以import過來
如下圖所示：
下面就是基本使用舉例：
Python
#!/usr/bin/env python# -*- coding=utf-8 -*-#Using GPL v2"""Usage:Just A Template"""from __future__ import division import sys,timefrom progressbar import *total = 1000 #基本用法progress = ProgressBar()for i in progress(range(total)): time.sleep(0.01) pbar = ProgressBar().start()for i in range(1,1000): pbar.update(int((i/(total-1))*100)) time.sleep(0.01)pbar.finish() #高級用法widgets = ['Progress: ', Percentage(), ' ', Bar(marker=RotatingMarker('>-=')), ' ', ETA(), ' ', FileTransferSpeed()]pbar = ProgressBar(widgets=widgets, maxval=10000000).start()for i in range(1000000): # do something pbar.update(10*i+1) time.sleep(0.0001)pbar.finish() 官方示例:http://code.google.com/p/python-progressbar/source/browse/progressbar/examples.py
Python
# coding:utf-8import sysimport timefrom progressbar import AnimatedMarker, Bar, BouncingBar, Counter, ETA, / FileTransferSpeed, FormatLabel, Percentage, / ProgressBar, ReverseBar, RotatingMarker, / SimpleProgress, Timer examples = [] def example(fn): try: name = 'Example %d' % int(fn.__name__[7:]) except: name = fn.__name__ def wrapped(): try: sys.stdout.write('Running: %s/n' % name) fn() sys.stdout.write('/n') except KeyboardInterrupt: sys.stdout.write('/nSkipping example./n/n') examples.append(wrapped) return wrapped @exampledef example0(): pbar = ProgressBar(widgets=[Percentage(), Bar()], maxval=300).start() for i in range(300): time.sleep(0.01) pbar.update(i + 1) pbar.finish() @exampledef example1(): widgets = ['Test: ', Percentage(), ' ', Bar(marker=RotatingMarker()), ' ', ETA(), ' ', FileTransferSpeed()] pbar = ProgressBar(widgets=widgets, maxval=10000000).start() for i in range(1000000): # do something pbar.update(10 * i + 1) pbar.finish() @exampledef example2(): class CrazyFileTransferSpeed(FileTransferSpeed): """It's bigger between 45 and 80 percent.""" def update(self, pbar): if 45 < pbar.percentage() < 80: return 'Bigger Now ' + FileTransferSpeed.update(self, pbar) else: return FileTransferSpeed.update(self, pbar) widgets = [CrazyFileTransferSpeed(), ' <<<', Bar(), '>>> ', Percentage(), ' ', ETA()] pbar = ProgressBar(widgets=widgets, maxval=10000000) # maybe do something pbar.start() for i in range(2000000): # do something pbar.update(5 * i + 1) pbar.finish() @exampledef example3(): widgets = [Bar('>'), ' ', ETA(), ' ', ReverseBar('<')] pbar = ProgressBar(widgets=widgets, maxval=10000000).start() for i in range(1000000): # do something pbar.update(10 * i + 1) pbar.finish() @exampledef example4(): widgets = ['Test: ', Percentage(), ' ', Bar(marker='0', left='[', right=']'), ' ', ETA(), ' ', FileTransferSpeed()] pbar = ProgressBar(widgets=widgets, maxval=500) pbar.start() for i in range(100, 500 + 1, 50): time.sleep(0.2) pbar.update(i) pbar.finish() @exampledef example5(): pbar = ProgressBar(widgets=[SimpleProgress()], maxval=17).start() for i in range(17): time.sleep(0.2) pbar.update(i + 1) pbar.finish() @exampledef example6(): pbar = ProgressBar().start() for i in range(100): time.sleep(0.01) pbar.update(i + 1) pbar.finish() @exampledef example7(): pbar = ProgressBar() # Progressbar can guess maxval automatically. for i in pbar(range(80)): time.sleep(0.01) @exampledef example8(): pbar = ProgressBar(maxval=80) # Progressbar can't guess maxval. for i in pbar((i for i in range(80))): time.sleep(0.01) @exampledef example9(): pbar = ProgressBar(widgets=['Working: ', AnimatedMarker()]) for i in pbar((i for i in range(50))): time.sleep(.08) @exampledef example10(): widgets = ['Processed: ', Counter(), ' lines (', Timer(), ')'] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(150))): time.sleep(0.1) @exampledef example11(): widgets = [FormatLabel('Processed: %(value)d lines (in: %(elapsed)s)')] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(150))): time.sleep(0.1) @exampledef example12(): widgets = ['Balloon: ', AnimatedMarker(markers='.oO<a href="http://www.jobbole.com/members/weiboyes8848">@*</a> ')] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(24))): time.sleep(0.3) @exampledef example13(): # You may need python 3.x to see this correctly try: widgets = ['Arrows: ', AnimatedMarker(markers='←↖↑↗→↘↓↙')] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(24))): time.sleep(0.3) except UnicodeError: sys.stdout.write('Unicode error: skipping example') @exampledef example14(): # You may need python 3.x to see this correctly try: widgets = ['Arrows: ', AnimatedMarker(markers='◢◣◤◥')] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(24))): time.sleep(0.3) except UnicodeError: sys.stdout.write('Unicode error: skipping example') @exampledef example15(): # You may need python 3.x to see this correctly try: widgets = ['Wheels: ', AnimatedMarker(markers='????')] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(24))): time.sleep(0.3) except UnicodeError: sys.stdout.write('Unicode error: skipping example') @exampledef example16(): widgets = [FormatLabel('Bouncer: value %(value)d - '), BouncingBar()] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(180))): time.sleep(0.05) @exampledef example17(): widgets = [FormatLabel('Animated Bouncer: value %(value)d - '), BouncingBar(marker=RotatingMarker())] pbar = ProgressBar(widgets=widgets) for i in pbar((i for i in range(180))): time.sleep(0.05) @exampledef example18(): widgets = [Percentage(), ' ', Bar(), ' ', ETA(), ' ', AdaptiveETA()] pbar = ProgressBar(widgets=widgets, maxval=500) pbar.start() for i in range(500): time.sleep(0.01 + (i < 100) * 0.01 + (i > 400) * 0.9) pbar.update(i + 1) pbar.finish() @exampledef example19(): pbar = ProgressBar() for i in pbar([]): pass pbar.finish() try: for example in examples: example()except KeyboardInterrupt: sys.stdout('/nQuitting examples./n') 再發(fā)一個類：
Python
#!/usr/bin/env python# -*- coding=utf-8 -*-#Using GPL v2"""Usage:Just A Template"""class progressbarClass: def __init__(self, finalcount, progresschar=None): import sys self.finalcount=finalcount self.blockcount=0 # # See if caller passed me a character to use on the # progress bar (like "*"). If not use the block # character that makes it look like a real progress # bar. # if not progresschar: self.block=chr(178) else: self.block=progresschar # # Get pointer to sys.stdout so I can use the write/flush # methods to display the progress bar. # self.f=sys.stdout # # If the final count is zero, don't start the progress gauge # if not self.finalcount : return self.f.write('/n------------------- % Progress -------------------/n') return def progress(self, count): # # Make sure I don't try to go off the end (e.g. >100%) # count=min(count, self.finalcount) # # If finalcount is zero, I'm done # if self.finalcount: percentcomplete=int(round(100*count/self.finalcount)) if percentcomplete < 1: percentcomplete=1 else: percentcomplete=100 #print "percentcomplete=",percentcomplete blockcount=int(percentcomplete/2) #print "blockcount=",blockcount if blockcount > self.blockcount: for i in range(self.blockcount,blockcount): self.f.write(self.block) self.f.flush() if percentcomplete == 100: self.f.write("/n") self.blockcount=blockcount return if __name__ == "__main__": from time import sleep pb=progressbarClass(8,"*") count=0 while count<9: count+=1 pb.progress(count) sleep(0.2) 另外，python cookbook中11.1節(jié)也提供了一個不錯的進度條類，代碼如下：
Python
import sys class progressbar(object): def __init__(self, finalcount, block_char='.'): self.finalcount = finalcount self.blockcount = 0 self.block = block_char self.f = sys.stdout if not self.finalcount: return self.f.write('/n------------------ % Progress -------------------1/n') self.f.write(' 1 2 3 4 5 6 7 8 9 0/n') self.f.write('----0----0----0----0----0----0----0----0----0----0/n') def progress(self, count): count = min(count, self.finalcount) if self.finalcount: percentcomplete = int(round(100.0 * count / self.finalcount)) if percentcomplete < 1: percentcomplete = 1 else: percentcomplete = 100 blockcount = int(percentcomplete // 2) if blockcount <= self.blockcount: return for i in range(self.blockcount, blockcount): self.f.write(self.block) self.f.flush() self.blockcount = blockcount if percentcomplete == 100: self.f.write("/n") if __name__ == "__main__": from time import sleep pb = progressbar(8, "*") for count in range(1, 9): pb.progress(count) sleep(0.2) pb = progressbar(100) pb.progress(20) sleep(0.3) pb.progress(47) sleep(0.3) pb.progress(90) sleep(0.3) pb.progress(100) print "testing 1:" pb = progressbar(1) pb.progress(1) 運行結(jié)果如下圖所示：
希望本文所述對大家Python程序設計的學習有所幫助。
