多线程对全局变量修改和单线程对全局变量修改

线程过多了，不会比单线程快多少。因为程序可能花时间在线程的转换上了。threading模块没有返回值。

import threading

import time

ind=4

dan_sum=0

multi_sum=0

def single():

    for j in range(ind):

        for i in range(5000):

            print(i*2)

            global dan_sum

            dan_sum=dan_sum+i*2

def s():

    for i in range(5000):

        print(i*2)

        global multi_sum

        multi_sum=multi_sum+i*2

def multi():

    threa=[]

    for j in range(ind):

        threa.append(threading.Thread(target=s))

    for t in threa:

        t.start()

    for t in threa:

        t.join()

if __name__ == '__main__':

    start=time.time()

    single()

    end=time.time()

    sum=0

    sum1=0

    sum=end-start

    start=time.time()

    multi()

    end=time.time()

    sum1=end-start

    print('single',sum,'multi',sum1,dan_sum,multi_sum)