python 使用多线程报错：AttributeError: Can't pickle local object

报错信息：
Traceback (most recent call last):
File “D:/flaskProject/test.py”, line 35, in test
pool.apply(self.out, args=(i,))
File “Python37-32\lib\multiprocessing\pool.py", line 261, in apply
return self.apply_async(func, args, kwds).get()
File "\lib\multiprocessing\pool.py”, line 657, in get
raise self._value
File “\Python37-32\lib\multiprocessing\pool.py", line 431, in _handle_tasks
put(task)
File "\Python37-32\lib\multiprocessing\connection.py”, line 206, in send
self._send_bytes(_ForkingPickler.dumps(obj))
File “*\Python37-32\lib\multiprocessing\reduction.py”, line 51, in dumps
cls(buf, protocol).dump(obj)
TypeError: can’t pickle _thread._local objects

原类的构造函数：
class threadtest:

def __init__(self, ipList, user, password):
    self.ipList = ipList
    self.httpAuth = HTTPDigestAuth(user, password)
    return

def out(self, i):
    url = "http://" + i + "/name"
    response = requests.get(url, self.httpAuth)
    print(response.text)
    return

def test(self):
    pool = Pool(processes=2)
    for i in self.ipList:
        pool.apply(self.out, args=(i,))
    pool.close()
    pool.join()
    return

if name == ‘main’:
ipList = [‘192.168.2.1’, ‘192.168.2.2’, ‘192.168.2.3’, ‘192.168.2.4’, ‘192.168.2.5’, ]
a = threadtest(ipList, ‘admin’, ‘admin’)
a.test()

原因：
在class中对属性进行初始化使用了其它类返回的句柄进行初始化导致，HTTPDigestAuth的返回值不能进行序列化，也就是不能作为cls(buf, protocol).dump(obj)的参数进行序列化。

将self.httpAuth = HTTPDigestAuth(httpUser, httpPassword)修改为：
self.httpUser
self.httpPassword
并将函数HTTPDigestAuth放到类的方法中

修改后：
class threadtest:

def __init__(self, ipList, user, password):
    self.ipList = ipList
    self.user = user
    self.password = password
    return

def out(self, i):
    url = "http://" + i + "/name"
    response = requests.get(url, HTTPDigestAuth(self.user, self.password))
    print(response.text)
    return

def test(self):
    pool = Pool(processes=2)
  for i in self.ipList:
        pool.apply(self.out, args=(i,))
    pool.close()
    pool.join()
    return

if name == ‘main’:
ipList = [‘192.168.2.1’, ‘192.168.2.2’, ‘192.168.2.3’, ‘192.168.2.4’, ‘192.168.2.5’, ]
a = threadtest(ipList, ‘admin’, ‘admin’)
a.test()