TensorFlow IOError:没有到主机的路由

我正在尝试在Juypter笔记本中使用以下代码:

import tensorflow as tf
import tensorflow.examples.tutorials.mnist.input_data as input_data
mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)

但出现了以下错误:

Extracting MNIST_data/train-images-idx3-ubyte.gz
---------------------------------------------------------------------------
IOError                                   Traceback (most recent call last)
<ipython-input-9-aeeb0aa14838> in <module>()
      3 import tensorflow.examples.tutorials.mnist.input_data as input_data
----> 4 mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)
      5 print("MNIST downloaded.")

/usr/local/lib/python2.7/site-packages/tensorflow/python/util/deprecation.pyc in new_func(*args, **kwargs)
    248               'in a future version' if date is None else ('after %s' % date),
    249               instructions)
--> 250       return func(*args, **kwargs)
    251     return tf_decorator.make_decorator(
    252         func, new_func, 'deprecated',

/usr/local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/datasets/mnist.pyc in read_data_sets(train_dir, fake_data, one_hot, dtype, reshape, validation_size, seed, source_url)
    263 
    264   local_file = base.maybe_download(TRAIN_LABELS, train_dir,
--> 265                                    source_url + TRAIN_LABELS)
    266   with gfile.Open(local_file, 'rb') as f:
    267     train_labels = extract_labels(f, one_hot=one_hot)

/usr/local/lib/python2.7/site-packages/tensorflow/python/util/deprecation.pyc in new_func(*args, **kwargs)
    248               'in a future version' if date is None else ('after %s' % date),
    249               instructions)
--> 250       return func(*args, **kwargs)
    251     return tf_decorator.make_decorator(
    252         func, new_func, 'deprecated',

/usr/local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/datasets/base.pyc in maybe_download(filename, work_directory, source_url)
    250   filepath = os.path.join(work_directory, filename)
    251   if not gfile.Exists(filepath):
--> 252     temp_file_name, _ = urlretrieve_with_retry(source_url)
    253     gfile.Copy(temp_file_name, filepath)
    254     with gfile.GFile(filepath) as f:

/usr/local/lib/python2.7/site-packages/tensorflow/python/util/deprecation.pyc in new_func(*args, **kwargs)
    248               'in a future version' if date is None else ('after %s' % date),
    249               instructions)
--> 250       return func(*args, **kwargs)
    251     return tf_decorator.make_decorator(
    252         func, new_func, 'deprecated',

/usr/local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/datasets/base.pyc in wrapped_fn(*args, **kwargs)
    203       for delay in delays():
    204         try:
--> 205           return fn(*args, **kwargs)
    206         except Exception as e:  # pylint: disable=broad-except
    207           if is_retriable is None:

/usr/local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/datasets/base.pyc in urlretrieve_with_retry(url, filename)
    231 @_internal_retry(initial_delay=1.0, max_delay=16.0, is_retriable=_is_retriable)
    232 def urlretrieve_with_retry(url, filename=None):
--> 233   return urllib.request.urlretrieve(url, filename)
    234 
    235 

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.pyc in urlretrieve(url, filename, reporthook, data, context)
     96     else:
     97         opener = _urlopener
---> 98     return opener.retrieve(url, filename, reporthook, data)
     99 def urlcleanup():
    100     if _urlopener:

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.pyc in retrieve(self, url, filename, reporthook, data)
    243             except IOError:
    244                 pass
--> 245         fp = self.open(url, data)
    246         try:
    247             headers = fp.info()

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.pyc in open(self, fullurl, data)
    211         try:
    212             if data is None:
--> 213                 return getattr(self, name)(url)
    214             else:
    215                 return getattr(self, name)(url, data)

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.pyc in open_https(self, url, data)
    441             if realhost: h.putheader('Host', realhost)
    442             for args in self.addheaders: h.putheader(*args)
--> 443             h.endheaders(data)
    444             errcode, errmsg, headers = h.getreply()
    445             fp = h.getfile()

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.pyc in endheaders(self, message_body)
   1036         else:
   1037             raise CannotSendHeader()
-> 1038         self._send_output(message_body)
   1039 
   1040     def request(self, method, url, body=None, headers={}):

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.pyc in _send_output(self, message_body)
    880             msg += message_body
    881             message_body = None
--> 882         self.send(msg)
    883         if message_body is not None:
    884             #message_body was not a string (i.e. it is a file) and

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.pyc in send(self, data)
    842         if self.sock is None:
    843             if self.auto_open:
--> 844                 self.connect()
    845             else:
    846                 raise NotConnected()

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.pyc in connect(self)
   1253             "Connect to a host on a given (SSL) port."
   1254 
-> 1255             HTTPConnection.connect(self)
   1256 
   1257             if self._tunnel_host:

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/httplib.pyc in connect(self)
    819         """Connect to the host and port specified in __init__."""
    820         self.sock = self._create_connection((self.host,self.port),
--> 821                                            self.timeout, self.source_address)
    822 
    823         if self._tunnel_host:

/usr/local/Cellar/python@2/2.7.15/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.pyc in create_connection(address, timeout, source_address)
    573 
    574     if err is not None:
--> 575         raise err
    576     else:
    577         raise error("getaddrinfo returns an empty list")

IOError: [Errno socket error] [Errno 65] No route to host

知道为什么吗?谢谢。