python主要是通過thread和threading這兩個模塊來實現多線程支持。
python的thread模塊是比較底層的模塊，python的threading模塊是對thread做了一些封裝，能夠更加方便的被使用。可是python（cpython）因為GIL的存在無法使用threading充分利用CPU資源，假設想充分發揮多核CPU的計算能力須要使用multiprocessing模塊(Windows下使用會有諸多問題)。
假設在對線程應用有較高的要求時能夠考慮使用Stackless Python來完畢。Stackless Python是Python的一個改動版本號，對多線程編程有更好的支持，提供了對微線程的支持。微線程是輕量級的線程，在多個線程間切換所需的時間很多其它，占用資源也更少。
通過threading模塊創建新的線程有兩種方法：一種是通過threading.Thread(Target=executable Method)-即傳遞給Thread對象一個可運行方法（或對象）;另外一種是繼承threading.Thread定義子類並重寫run()方法。另外一種方法中，唯一必須重寫的方法是run()，可依據需要決定是否重寫__init__()。值得注意的是，若要重寫__init__()，父類的__init__()必需要在函數第一行調用，否則會觸發錯誤“AssertionError: Thread.__init__() not called”
Python threading模塊不同於其它語言之處在於它沒有提供線程的終止方法，通過Python threading.Thread()啟動的線程彼此是獨立的。若在線程A中啟動了線程B，那么A、B是彼此獨立執行的線程。若想終止線程A的同一時候強力終止線程B。一個簡單的方法是通過在線程A中調用B.setDaemon(True)實現。
但這樣帶來的問題是：線程B中的資源（打開的文件、傳輸數據等）可能會沒有正確的釋放。所以setDaemon()並不是一個好方法,更為妥當的方式是通過Event機制。以下這段程序體現了setDaemon()和Event機制終止子線程的差別。
import threading
import time
class mythread(threading.Thread):
def __init__(self,stopevt = None,File=None,name = 'subthread',Type ='event'):
threading.Thread.__init__(self)
self.stopevt = stopevt
self.name = name
self.File = File
self.Type = Type
def Eventrun(self):
while not self.stopevt.isSet():
print self.name +' alive\n'
time.sleep(2)
if self.File:
print 'close opened file in '+self.name+'\n'
self.File.close()
print self.name +' stoped\n'
def Daemonrun(self):
D = mythreadDaemon(self.File)
D.setDaemon(True)
while not self.stopevt.isSet():
print self.name +' alive\n'
time.sleep(2)
print self.name +' stoped\n'
def run(self):
if self.Type == 'event': self.Eventrun()
else: self.Daemonrun()
class mythreadDaemon(threading.Thread):
def __init__(self,File=None,name = 'Daemonthread'):
threading.Thread.__init__(self)
self.name = name
self.File = File
def run(self):
while True:
print self.name +' alive\n'
time.sleep(2)
if self.File:
print 'close opened file in '+self.name+'\n'
self.File.close()
print self.name +' stoped\n'
def evtstop():
stopevt = threading.Event()
FileA = open('testA.txt','w')
FileB = open('testB.txt','w')
A = mythread(stopevt,FileA,'subthreadA')
B = mythread(stopevt,FileB,'subthreadB')
print repr(threading.currentThread())+'alive\n'
print FileA.name + ' closed? '+repr(FileA.closed)+'\n'
print FileB.name + ' closed? '+repr(FileB.closed)+'\n'
A.start()
B.start()
time.sleep(1)
print repr(threading.currentThread())+'send stop signal\n'
stopevt.set()
A.join()
B.join()
print repr(threading.currentThread())+'stoped\n'
print 'after A stoped, '+FileA.name + ' closed? '+repr(FileA.closed)+'\n'
print 'after A stoped, '+FileB.name + ' closed?
'+repr(FileB.closed)+'\n'
def daemonstop():
stopevt = threading.Event()
FileA = open('testA.txt','r')
A = mythread(stopevt,FileA,'subthreadA',Type = 'Daemon')
print repr(threading.currentThread())+'alive\n'
print FileA.name + ' closed?
'+repr(FileA.closed)+'\n'
A.start()
time.sleep(1)
stopevt.set()
A.join()
print repr(threading.currentThread())+'stoped\n'
print 'after A stoped, '+FileA.name + ' closed? '+repr(FileA.closed)+'\n'
if not FileA.closed:
print 'You see the differents, the resource in subthread may not released with setDaemon()'
FileA.close()
if __name__ =='__main__':
print '-------stop subthread example with Event:----------\n'
evtstop()
print '-------Daemon stop subthread example :----------\n'
daemonstop()
執行結果是：
-------stop subthread example with Event:---------- <_MainThread(MainThread, started 2436)>alive testA.txt closed?False testB.txt closed? False subthreadA alive subthreadB alive <_MainThread(MainThread, started 2436)>send stop signal close opened file in subthreadA close opened file in subthreadB subthreadA stoped subthreadB stoped <_MainThread(MainThread, started 2436)>stoped after A stoped, testA.txt closed? True after A stoped, testB.txt closed?
True -------Daemon stop subthread example :---------- <_MainThread(MainThread, started 2436)>alive testA.txt closed?
False subthreadA alive subthreadA stoped <_MainThread(MainThread, started 2436)>stoped after A stoped, testA.txt closed? False You see the differents, the resource in subthread may not released with setDaemon()