catch exceptions when no internet connection

[dmalan]

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connection.py", line 160, in _new_conn
    (self._dns_host, self.port), self.timeout, **extra_kw)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/util/connection.py", line 57, in create_connection
    for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/socket.py", line 745, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno 8] nodename nor servname provided, or not known

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connectionpool.py", line 603, in urlopen
    chunked=chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connectionpool.py", line 344, in _make_request
    self._validate_conn(conn)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connectionpool.py", line 843, in _validate_conn
    conn.connect()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connection.py", line 316, in connect
    conn = self._new_conn()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connection.py", line 169, in _new_conn
    self, "Failed to establish a new connection: %s" % e)
urllib3.exceptions.NewConnectionError: <urllib3.connection.VerifiedHTTPSConnection object at 0x10f9f5828>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/adapters.py", line 449, in send
    timeout=timeout
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/connectionpool.py", line 641, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/urllib3/util/retry.py", line 399, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='auth.docker.io', port=443): Max retries exceeded with url: /token?scope=repository:cs50/cli:pull&service=registry.docker.io (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x10f9f5828>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known',))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/bin/cli50", line 11, in <module>
    load_entry_point('cli50==3.3.0', 'console_scripts', 'cli50')()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/cli50/__main__.py", line 157, in main
    response = requests.get(f"https://auth.docker.io/token?scope=repository:{IMAGE}:pull&service=registry.docker.io")
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/api.py", line 75, in get
    return request('get', url, params=params, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/api.py", line 60, in request
    return session.request(method=method, url=url, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/sessions.py", line 533, in request
    resp = self.send(prep, **send_kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/sessions.py", line 646, in send
    r = adapter.send(request, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/requests/adapters.py", line 516, in send
    raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPSConnectionPool(host='auth.docker.io', port=443): Max retries exceeded with url: /token?scope=repository:cs50/cli:pull&service=registry.docker.io (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x10f9f5828>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known',))