各位好，我用python 寫了一個可以下載youtube 影片的功能
但執行下出現了一些錯誤，但找網路上也好像找不太到解法
以下是我的程式碼

from pytube import YouTube

link = "https://www.youtube.com/watch?v=X8WkCAAD2gI"
yt = YouTube(link)
stream = yt.streams.first()
stream.download('./youtube')

然後附上我的環境，我是以vituralenv下的方式執行的
python 3.6.4
pip pip 18.0 from {環境資料夾}/lib/python3.6/site-packages/pip (python 3.6)

我的module 如下（我也很確定有安裝pytube）(以下僅列出我覺得重要的modules)

Package Version
certifi 2018.8.24
pip 18.0
pytube 9.2.3
requests 2.19.1
setuptools 40.2.0
urllib3 1.23
wheel 0.31.1

執行後出現的錯誤如下（看來是ssl 的問題，但我該如何解？）

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 1318, in do_open
    encode_chunked=req.has_header('Transfer-encoding'))
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 1239, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 1285, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 1234, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 1026, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 964, in send
    self.connect()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/http/client.py", line 1400, in connect
    server_hostname=server_hostname)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 407, in wrap_socket
    _context=self, _session=session)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 814, in __init__
    self.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 1068, in do_handshake
    self._sslobj.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 689, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:777)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "newyoutube.py", line 4, in <module>
    yt = YouTube(link)
  File "..../lib/python3.6/site-packages/pytube/__main__.py", line 88, in __init__
    self.prefetch_init()
  File "..../lib/python3.6/site-packages/pytube/__main__.py", line 96, in prefetch_init
    self.prefetch()
  File "..../lib/python3.6/site-packages/pytube/__main__.py", line 160, in prefetch
    self.watch_html = request.get(url=self.watch_url)
  File "..../lib/python3.6/site-packages/pytube/request.py", line 21, in get
    response = urlopen(url)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 223, in urlopen
    return opener.open(url, data, timeout)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 526, in open
    response = self._open(req, data)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 544, in _open
    '_open', req)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 504, in _call_chain
    result = func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 1361, in https_open
    context=self._context, check_hostname=self._check_hostname)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 1320, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:777)>

哈 錯誤有點多，有點意外，我也只是按照readme 貼上去執行的而已啊？ 好奇是我哪裡寫錯了還是什麼東西沒有安裝嗎？