下面的程式碼主要是使用一個類對外部資料（myList）進行修改，由於兩個執行緒同時對myList修改，在不加鎖的情況下，可能導致資料被不安全修改。
讀者可嘗試將“開啟鎖”和“釋放鎖”註釋，重執行，看效果。

#!/usr/local/bin/python
# coding: utf-8

import threading
import time

class ChangeVal(threading.Thread):
    # 繼承threading.Thread並初始化，相當於建構函式
    def __init__(self, myList, changeType, threadLock):
        threading.Thread.__init__(self)
        # self.myList 會指向外部傳入的myList的同一個實體地址。相當於傳入了C++的引用型別。
 

        self.myList = myList
        self.changeType = changeType
        self.threadLock = threadLock

    # 重寫run
    def run(self):
        # 開啟鎖
        self.threadLock.acquire()
        if self.changeType:
            self.change1()
        else:
            self.change2()
        # 釋放鎖
        self.threadLock.release()

    # 將myList資料全部改為1
 

    def change1(self):
        for i in range(len(self.myList)):
            time.sleep(1)
            self.myList[i] = 1
        print "in change1:" + str(self.myList)

    # 將myList資料全部改為2
    def change2(self):
        for i in range(len(self.myList)):
            time.sleep(1)
            self.myList[i] = 2
 

        print "in change2:" + str(self.myList)

if __name__ == "__main__":
    # 初始化用於給多個執行緒操作的資料
    myList = [0 for i in range(10)]
    # 初始化鎖的物件
    threadLock = threading.Lock()
    thread1 = ChangeVal(myList, True, threadLock)
    thread2 = ChangeVal(myList, False, threadLock)

    threads = [thread1, thread2]
    print "origin is:" + str(myList)
    thread1.start()
    thread2.start()

    # 等待所有執行緒結束
    for t in threads:
        t.join()
    print "all threads exit"