在python中学习队列模块(如何运行它)
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最近引入了队列设计,关于延迟处理能力以及实现“FIFO”等.
查看文档以尝试获取示例队列,以了解如何在我自己的设计/程序中实现它.但我遇到运行此代码的问题:
import queue
def worker():
while True:
item = q.get()
do_work(item)
q.task_done()
def main():
q = queue.Queue(maxsize=0)
for i in range(num_worker_threads):
t = Thread(target=worker)
t.daemon = True
t.start()
for item in source():
q.put(item)
q.join() # block until all tasks are done
main()
问题:希望有人解释for循环正在做什么,我只是运行代码时出错,所以我不得不遗漏一些东西.
出现问题错误:
NameError:未定义全局名称’num_worker_threads’
谢谢-Python新手 –
解决方法:
for循环启动了许多工作线程来执行“worker”定义的功能.这是应该在python 2.7中运行在您的系统上的工作代码.
import Queue
import threading
# input queue to be processed by many threads
q_in = Queue.Queue(maxsize=0)
# output queue to be processed by one thread
q_out = Queue.Queue(maxsize=0)
# number of worker threads to complete the processing
num_worker_threads = 10
# process that each worker thread will execute until the Queue is empty
def worker():
while True:
# get item from queue, do work on it, let queue know processing is done for one item
item = q_in.get()
q_out.put(do_work(item))
q_in.task_done()
# squares a number and returns the number and its square
def do_work(item):
return (item,item*item)
# another queued thread we will use to print output
def printer():
while True:
# get an item processed by worker threads and print the result. Let queue know item has been processed
item = q_out.get()
print "%d squared is : %d" % item
q_out.task_done()
# launch all of our queued processes
def main():
# Launches a number of worker threads to perform operations using the queue of inputs
for i in range(num_worker_threads):
t = threading.Thread(target=worker)
t.daemon = True
t.start()
# launches a single "printer" thread to output the result (makes things neater)
t = threading.Thread(target=printer)
t.daemon = True
t.start()
# put items on the input queue (numbers to be squared)
for item in range(10):
q_in.put(item)
# wait for two queues to be emptied (and workers to close)
q_in.join() # block until all tasks are done
q_out.join()
print "Processing Complete"
main()
@handle的Python 3版本
import queue
import threading
# input queue to be processed by many threads
q_in = queue.Queue(maxsize=0)
# output queue to be processed by one thread
q_out = queue.Queue(maxsize=0)
# number of worker threads to complete the processing
num_worker_threads = 10
# process that each worker thread will execute until the Queue is empty
def worker():
while True:
# get item from queue, do work on it, let queue know processing is done for one item
item = q_in.get()
q_out.put(do_work(item))
q_in.task_done()
# squares a number and returns the number and its square
def do_work(item):
return (item,item*item)
# another queued thread we will use to print output
def printer():
while True:
# get an item processed by worker threads and print the result. Let queue know item has been processed
item = q_out.get()
print("{0[0]} squared is : {0[1]}".format(item) )
q_out.task_done()
# launch all of our queued processes
def main():
# Launches a number of worker threads to perform operations using the queue of inputs
for i in range(num_worker_threads):
t = threading.Thread(target=worker)
t.daemon = True
t.start()
# launches a single "printer" thread to output the result (makes things neater)
t = threading.Thread(target=printer)
t.daemon = True
t.start()
# put items on the input queue (numbers to be squared)
for item in range(10):
q_in.put(item)
# wait for two queues to be emptied (and workers to close)
q_in.join() # block until all tasks are done
q_out.join()
print( "Processing Complete" )
main()
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