python - Python中多处理或多线程的动态刷新打印

Question

我已经实现了一个多进程下载器。 如何打印可以自动刷新的状态栏(完成率，下载速度) 在终端的不同部分。

像这样:

    499712  [6.79%]   68k/s     // keep refreshing
    122712  [16.79%]   42k/s    // different process/thread
     99712  [56.32%]   10k/s

代码:

download(...)
...
    f = open(tmp_file_path, 'wb')
    print "Downloading: %s Bytes: %s" % (self.file_name, self.file_size)
    file_size_dl = 0
    block_sz = 8192
    start_time = time.time()
    while True:
        buffer = self.opening.read(block_sz)
        if not buffer:
            break

        file_size_dl += len(buffer)
        f.write(buffer)
        end_time = time.time()
        cost_time = end_time - start_time
        if cost_time == 0:
            cost_time = 1
        status = "\r%10d  [%3.2f%%]  %3dk/s" % (file_size_dl,
                file_size_dl * 100. / self.file_size,
                file_size_dl * 100. / 1024 / 1024 / cost_time)
        print status,
        sys.stdout.flush()
    f.close()

DownloadProcess继承Process类并触发下载方法。

我使用队列来存储 url。下面是启动过程

  ...
  for i in range(3):
    t = DownloadProcess(queue)
    t.start()
    for url in urls:
        queue.put(url)
  queue.join()

Answer 1

下面是一个同时实现了多处理和多线程的demo。要尝试其中一个，只需取消注释代码顶部的导入行。如果您在单行上有一个进度条，那么您可以使用打印 '\r' 的技术将光标移回该行的开头。但是如果你想拥有多行进度条，那么你将不得不变得更花哨一些。每次我想打印进度条时，我只是清空屏幕。查看文章 console output on Unix in Python它对我生成下面的代码有很大帮助。他展示了这两种技术。您还可以试试 curses 库，它是 python 标准库的一部分。问题Multiline progress bars问类似的事情。主线程/进程生成执行工作的子线程，并使用队列将它们的进度传回主线程。我强烈建议使用队列进行进程间/线程间通信。然后主线程显示进度并等待所有子线程结束执行，然后退出。

代码

import time, random, sys, collections
from multiprocessing import Process as Task, Queue
#from threading import Thread as Task
#from Queue import Queue

def download(status, filename):
    count = random.randint(5, 30)
    for i in range(count):
        status.put([filename, (i+1.0)/count])
        time.sleep(0.1)

def print_progress(progress):
    sys.stdout.write('\033[2J\033[H') #clear screen
    for filename, percent in progress.items():
        bar = ('=' * int(percent * 20)).ljust(20)
        percent = int(percent * 100)
        sys.stdout.write("%s [%s] %s%%\n" % (filename, bar, percent))
    sys.stdout.flush()

def main():
    status = Queue()
    progress = collections.OrderedDict()
    workers = []
    for filename in ['test1.txt', 'test2.txt', 'test3.txt']:
        child = Task(target=download, args=(status, filename))
        child.start()
        workers.append(child)
        progress[filename] = 0.0
    while any(i.is_alive() for i in workers):
        time.sleep(0.1)
        while not status.empty():
            filename, percent = status.get()
            progress[filename] = percent
            print_progress(progress)
    print 'all downloads complete'

main()

演示