运行几个线程和同时运行几个不同的程序类似，它有以下好处：
- 一个进程内的多个线程和主线程分享相同的数据空间，比分开不同的过程更容易分享信息或者彼此通信。
- 线程有时叫做轻量化过程，而且他们不要求更多的内存开支；它们比过程便宜。
- 它可以被抢占（中断）
- 它能暂时被挂起（也叫做休眠），而别的线程在运行--这也叫做yielding（让步）。
开始一个新线程：
要生成一个线程，需要调用在thread模块中方法如下：thread.start_new_thread ( function, args[, kwargs] )
这种函数调用提供了创建新线程快速和有效的方法，适用于Windows和Linux。
方法立即返回，而子线程启动并调用函数，函数的参数为传递的args列表。当函数返回时，线程结束。
在这里，args是参数元组；调用函数而不传递任何参数使用空的元组。kwargs是可选的关键字参数字典。
例子：
#!/usr/bin/python
import thread
import time
# Define a function for the thread
def print_time( threadName, delay):
count = 0
while count < 5:
time.sleep(delay)
count += 1
print "%s: %s" % ( threadName, time.ctime(time.time()) )
# Create two threads as follows
try:
thread.start_new_thread( print_time, ("Thread-1", 2, ) )
thread.start_new_thread( print_time, ("Thread-2", 4, ) )
except:
print "Error: unable to start thread"
while 1:
pass
上述代码执行时，产生以下结果：
Thread-1: Thu Jan 22 15:42:17 2009
Thread-1: Thu Jan 22 15:42:19 2009
Thread-2: Thu Jan 22 15:42:19 2009
Thread-1: Thu Jan 22 15:42:21 2009
Thread-2: Thu Jan 22 15:42:23 2009
Thread-1: Thu Jan 22 15:42:23 2009
Thread-1: Thu Jan 22 15:42:25 2009
Thread-2: Thu Jan 22 15:42:27 2009
Thread-2: Thu Jan 22 15:42:31 2009
Thread-2: Thu Jan 22 15:42:35 2009
尽管对于低级别的线程，它是非常有效的，然而thread模块与较新的线程模块相比，其功能还是非常有限的。
Threading模块：
与前一节讨论的thread模块相比，从Python2.4开始包含的较新的threading模块，为线程提供了更多强大、高级的支持。threading模块包含了thread模块中所有的方法，并提供一些其余的方法：
- threading.activeCount():返回激活的线程对象的数目
- theading.currentThread():返回调用者的线程控制中线程对象的数目
- threading.enumerate(): 返回当前活动的线程对象列表
- run():线程的入口点
- start():调用run方法启动线程
- join(time):等待线程结束
- isAlive():检查一个线程是否仍旧在执行
- getName():返回线程的名字
- setName():设置一个线程的名字
使用Threading模块创建线程：
要使用threading模块实现一个新线程，你得先如下做：- 定义Thread类的一个子类。
- 重写__init__(self,[,args])方法以增加额外的参数
- 然后，重写run(self[,args])方法以实现线程启动后要做的事情
例子：
#!/usr/bin/python
import threading
import time
exitFlag = 0
class myThread (threading.Thread):
def __init__(self, threadID, name, counter):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.counter = counter
def run(self):
print "Starting " + self.name
print_time(self.name, self.counter, 5)
print "Exiting " + self.name
def print_time(threadName, delay, counter):
while counter:
if exitFlag:
thread.exit()
time.sleep(delay)
print "%s: %s" % (threadName, time.ctime(time.time()))
counter -= 1
# Create new threads
thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)
# Start new Threads
thread1.start()
thread2.start()
print "Exiting Main Thread"
上述代码执行后，它会产出如下结果：
Starting Thread-1
Starting Thread-2
Exiting Main Thread
Thread-1: Thu Mar 21 09:10:03 2013
Thread-1: Thu Mar 21 09:10:04 2013
Thread-2: Thu Mar 21 09:10:04 2013
Thread-1: Thu Mar 21 09:10:05 2013
Thread-1: Thu Mar 21 09:10:06 2013
Thread-2: Thu Mar 21 09:10:06 2013
Thread-1: Thu Mar 21 09:10:07 2013
Exiting Thread-1
Thread-2: Thu Mar 21 09:10:08 2013
Thread-2: Thu Mar 21 09:10:10 2013
Thread-2: Thu Mar 21 09:10:12 2013
Exiting Thread-2
同步线程：
Python提供的threading模块包括一个易于实现的锁定机制，以允许你同步线程。创建一个新锁通过调用Lock()实现，它也返回这个新锁。
新锁对象的accquire(blocking)方法，用来强制线程同步运行。可选的blocking参数使你能够控制线程是否请求锁。
如果blocking设置为0，线程在不能获取锁时立即返回0值；而blocking设置为1时，线程获取锁以后返回1值。如果blocking设置为1，线程将会阻塞，一直等到锁释放。
新锁对象的release()方法用来释放不再需要的锁。
例子：
#!/usr/bin/python
import threading
import time
class myThread (threading.Thread):
def __init__(self, threadID, name, counter):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.counter = counter
def run(self):
print "Starting " + self.name
# Get lock to synchronize threads
threadLock.acquire()
print_time(self.name, self.counter, 3)
# Free lock to release next thread
threadLock.release()
def print_time(threadName, delay, counter):
while counter:
time.sleep(delay)
print "%s: %s" % (threadName, time.ctime(time.time()))
counter -= 1
threadLock = threading.Lock()
threads = []
# Create new threads
thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)
# Start new Threads
thread1.start()
thread2.start()
# Add threads to thread list
threads.append(thread1)
threads.append(thread2)
# Wait for all threads to complete
for t in threads:
t.join()
print "Exiting Main Thread"
当上述代码执行后，它产生以下结果：
Starting Thread-1
Starting Thread-2
Thread-1: Thu Mar 21 09:11:28 2013
Thread-1: Thu Mar 21 09:11:29 2013
Thread-1: Thu Mar 21 09:11:30 2013
Thread-2: Thu Mar 21 09:11:32 2013
Thread-2: Thu Mar 21 09:11:34 2013
Thread-2: Thu Mar 21 09:11:36 2013
Exiting Main Thread
多线程优先级 队列：
Queue模块允许你创建一个新的队列对象，以盛放一定数量的项目。控制Queue有以下方法：
- get():从队列移除一个项目并返回它
- put():把项目放入队列
- qsize():返回当前队列中项目的数量
- empty():如果队列为空，返回True，反之为False
- full():如果队列满了返回True，反之为False
#!/usr/bin/python
import Queue
import threading
import time
exitFlag = 0
class myThread (threading.Thread):
def __init__(self, threadID, name, q):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.q = q
def run(self):
print "Starting " + self.name
process_data(self.name, self.q)
print "Exiting " + self.name
def process_data(threadName, q):
while not exitFlag:
queueLock.acquire()
if not workQueue.empty():
data = q.get()
queueLock.release()
print "%s processing %s" % (threadName, data)
else:
queueLock.release()
time.sleep(1)
threadList = ["Thread-1", "Thread-2", "Thread-3"]
nameList = ["One", "Two", "Three", "Four", "Five"]
queueLock = threading.Lock()
workQueue = Queue.Queue(10)
threads = []
threadID = 1
# Create new threads
for tName in threadList:
thread = myThread(threadID, tName, workQueue)
thread.start()
threads.append(thread)
threadID += 1
# Fill the queue
queueLock.acquire()
for word in nameList:
workQueue.put(word)
queueLock.release()
# Wait for queue to empty
while not workQueue.empty():
pass
# Notify threads it's time to exit
exitFlag = 1
# Wait for all threads to complete
for t in threads:
t.join()
print "Exiting Main Thread"
当上述代码执行后，它产生以下结果：
Starting Thread-1
Starting Thread-2
Starting Thread-3
Thread-1 processing One
Thread-2 processing Two
Thread-3 processing Three
Thread-1 processing Four
Thread-2 processing Five
Exiting Thread-3
Exiting Thread-1
Exiting Thread-2
Exiting Main Thread