我在Linux计算机上有一个Python 3.7脚本，该计算机试图在多个线程中运行一个函数，但是当我尝试时，出现以下错误：

Traceback (most recent call last):
  File "./test2.py",line 43,in <module>
    pt.ping_scanx()
  File "./test2.py",line 39,in ping_scanx
    par = Parallel(function=self.pingx,parameter_list=list,thread_limit=10)
  File "./test2.py",line 19,in __init__
    self._x = self._pool.starmap(function,parameter_list,chunksize=1)
  File "/usr/local/lib/python3.7/multiprocessing/pool.py",line 276,in starmap
    return self._map_async(func,iterable,starmapstar,chunksize).get()
  File "/usr/local/lib/python3.7/multiprocessing/pool.py",line 657,in get
    raise self._value
  File "/usr/local/lib/python3.7/multiprocessing/pool.py",line 431,in _handle_tasks
    put(task)
  File "/usr/local/lib/python3.7/multiprocessing/connection.py",line 206,in send
    self._send_bytes(_ForkingPickler.dumps(obj))
  File "/usr/local/lib/python3.7/multiprocessing/reduction.py",line 51,in dumps
    cls(buf,protocol).dump(obj)
TypeError: cannot serialize '_io.TextIOWrapper' object

这是我用来演示该问题的示例代码：

#!/usr/local/bin/python3.7
from multiprocessing import Pool
import pexpect   # Used to run SSH for sessions

class Parallel:

    def __init__(self,function,thread_limit=4):

        # Create new thread to hold our jobs
        self._pool = Pool(processes=thread_limit)

        self._x = self._pool.starmap(function,chunksize=1)

class PingTest():

    def __init__(self):
        self._pex = None

    def connect(self):
        self._pex = pexpect.spawn("ssh snorton@127.0.0.1")

    def pingx(self,target_ip,source_ip):
        print("PING {} {}".format(target_ip,source_ip))

    def ping_scanx(self):

        self.connect()

        list = [['8.8.8.8','96.53.16.93'],['8.8.8.8','96.53.16.93']]

        par = Parallel(function=self.pingx,thread_limit=10)


pt = PingTest()
pt.ping_scanx()

如果我未在pexpect.spawn中包含该行，则不会发生该错误。有人可以解释为什么我得到此错误，并提出解决方法吗？