python多線程,限制線程數

#encoding:utf8

import threading
import time

data = 0

def func(sleeptime):
    global data
    print threading.currentThread().getName()
    time.sleep(sleeptime)
threads = []

for i in range(0,40):
    t = threading.Thread(target=func,args=(i,))
    threads.append(t)

num = 0
for t in threads:
    t.start()
    while True:
        #判斷正在運行的線程數量,如果小於5則退出while循環,
        #進入for循環啟動新的進程.否則就一直在while循環進入死循環
        if(len(threading.enumerate()) < 5):
            break