Python线程: Multiline Progress Report

Question

我正在编写这个程序，它使用线程同时下载多个文件，并在屏幕上报告每个文件的进度。我使用一个不同的线程来下载每个文件。这没问题:

for file_url, filename in zip(file_urls, filenames):
    th = Thread(target=download_file, args=(file_url, filename))
    threads.append(th)
    th.start()

for thread in threads:
    thread.join()

问题是我无论如何都不知道我可以在屏幕上打印每个文件进度报告，如下所示:

    "Downloading 'example1.zip':  54366 bytes of 2240799  70.7%" 
    "Downloading 'example2.zip':  31712 bytes of 1924639  64.7%" 
    "Downloading 'example3.zip':  21712 bytes of 3224979  34.7%" 

以下代码片段适用于单行进度报告:

def chunk_report(bytes_so_far, total_size, filename):

    percent = float(bytes_so_far) / total_size
    percent = round(percent * 100, 2)
    print "Downloading '{0}':  {1} of {2}  {3:3.2g}% \r".format(filename,
                                        bytes_so_far, total_size, percent),

输出将如下所示:

    "Downloading 'example2.zip':  31712 bytes of 1924639  64.7%" 

每次线程调用此函数时，它都会更新该线程正在下载的文件的屏幕。

那么，问题是如何打印多行进度报告，就像我上面在 python 中演示的那样？

提前致谢。

Answer 1

我将使用队列向报告线程报告进度:

1. 创建队列
2. 生成每个下载线程，并将队列作为参数传递
3. 让每个下载将进度消息放入队列
4. 生成一个报告线程，从队列中读取进度消息并更新显示

模拟示例:

import threading
import time
import random
import Queue
import sys

# a downloading thread
def worker(path, total, q):
  size = 0
  while size < total:
    dt = random.randint(1,3)
    time.sleep(dt)
    ds = random.randint(1,5)
    size = size + ds
    if size > total: size = total
    q.put(("update", path, total, size))
  q.put(("done", path))

# the reporting thread
def reporter(q, nworkers):
  status = {}
  while nworkers > 0:
    msg = q.get()
    if msg[0] == "update":
      path, total, size = msg[1:]
      status[path] = (total, size)
      # update the screen here
      show_progress(status)
    elif msg[0] == "done":
      nworkers = nworkers - 1
  print ""

def show_progress(status):
  line = ""
  for path in status:
    (total, size) = status[path]
    line = line + "%s: %3d/%d   " % (path, size,total)
  sys.stdout.write("\r"+line)
  sys.stdout.flush()

def main():
  q = Queue.Queue()
  w1 = threading.Thread(target = worker, args = ("abc", 30, q) )
  w2 = threading.Thread(target = worker, args = ("foobar", 25, q))
  w3 = threading.Thread(target = worker, args = ("bazquux", 16, q))
  r = threading.Thread(target = reporter, args = (q, 3))
  for t in [w1,w2,w3,r]: t.start()
  for t in [w1,w2,w3,r]: t.join()

main()