初学Python遇到的坑

问题一

脚本内容

MacBookPro:Desktop mac$ cat wike.py
#!/usr/bin/python

from urllib.request import urlopen
from bs4 import BeautifulSoup
#import ssl

#ssl._create_default_https_context = ssl._create_unverified_context
html = urlopen("http://en.wikipedia.org/wiki/Kevin_Bacon")
bsObj = BeautifulSoup(html,"lxml")
for link in bsObj.findAll("a"):
    if 'href' in link.attrs:
        print(link.attrs['href'])

输出

报错

MacBookPro:Desktop mac$ python3 wike.py
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 1254, in do_open
    h.request(req.get_method(), req.selector, req.data, headers)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1106, in request
    self._send_request(method, url, body, headers)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1151, in _send_request
    self.endheaders(body)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1102, in endheaders
    self._send_output(message_body)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 934, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 877, in send
    self.connect()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/http/client.py", line 1260, in connect
    server_hostname=server_hostname)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 377, in wrap_socket
    _context=self)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 752, in __init__
    self.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 988, in do_handshake
    self._sslobj.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/ssl.py", line 633, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:645)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "wike.py", line 6, in <module>
    html = urlopen("http://en.wikipedia.org/wiki/Kevin_Bacon")
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 163, in urlopen
    return opener.open(url, data, timeout)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 472, in open
    response = meth(req, response)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 582, in http_response
    'http', request, response, code, msg, hdrs)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 504, in error
    result = self._call_chain(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 444, in _call_chain
    result = func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 696, in http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 466, in open
    response = self._open(req, data)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 484, in _open
    '_open', req)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 444, in _call_chain
    result = func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 1297, in https_open
    context=self._context, check_hostname=self._check_hostname)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/urllib/request.py", line 1256, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:645)>
MacBookPro:Desktop mac$ echo $?
1

出了一堆的错，然后在 http://stackoverflow.com/questions/27835619/ssl-certificate-verify-failed-error 找到了答案:

要引入 一个ssl 的模块，然后，就没有然后了

问题二

Could not fetch URL https://pypi.python.org/simple/nltk/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:749) - skipping
  Could not find a version that satisfies the requirement nltk (from versions: )
No matching distribution found for nltk

报了上面的错，下面的语句解决.

pip --trusted-host pypi.python.org install

问题三

<urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:645

　报了上面的错，下面的语句解决　

pip3 install certifi