Python3: HTTP Error 302 while using urllib

I want to read the value of different stocks from websites. Therefore I wrote this tiny script, which reads the page source and then parses out the value:

stock_reader.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from re import search
from urllib import request


def main():
    links = [
        [
            'CSG',
            'UBS',
        ],
        [
            'http://ift.tt/2y65nHA',
            'http://ift.tt/2jZgXOq',
        ],
    ]

    for i in in range(len(links[0])):
        url = links[1][i]
        htmltext = request.urlopen(url).read().decode('utf-8')
        source = htmltext.splitlines()
        for line in source:
            if 'id="bid"' in line:
                m = search('\d+.\d+', line)
                print('{}'.format(m.string[m.start():m.end()]))


if __name__ == '__main__':
    main()

sometimes it works but sometimes this error gets raised:

error message

Traceback (most recent call last):
  File "./aktien_reader.py", line 39, in <module>
    main()
  File "./aktien_reader.py", line 30, in main
    htmltext = request.urlopen(url).read().decode('utf-8')
  File "/usr/lib/python3.3/urllib/request.py", line 160, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/lib/python3.3/urllib/request.py", line 479, in open
    response = meth(req, response)
  File "/usr/lib/python3.3/urllib/request.py", line 591, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.3/urllib/request.py", line 511, in error
    result = self._call_chain(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 451, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 696, in http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "/usr/lib/python3.3/urllib/request.py", line 479, in open
    response = meth(req, response)
  File "/usr/lib/python3.3/urllib/request.py", line 591, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.3/urllib/request.py", line 511, in error
    result = self._call_chain(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 451, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 696, in http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "/usr/lib/python3.3/urllib/request.py", line 479, in open
    response = meth(req, response)
  File "/usr/lib/python3.3/urllib/request.py", line 591, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.3/urllib/request.py", line 511, in error
    result = self._call_chain(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 451, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 696, in http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "/usr/lib/python3.3/urllib/request.py", line 479, in open
    response = meth(req, response)
  File "/usr/lib/python3.3/urllib/request.py", line 591, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.3/urllib/request.py", line 511, in error
    result = self._call_chain(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 451, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 696, in http_error_302
    return self.parent.open(new, timeout=req.timeout)
  File "/usr/lib/python3.3/urllib/request.py", line 479, in open
    response = meth(req, response)
  File "/usr/lib/python3.3/urllib/request.py", line 591, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.3/urllib/request.py", line 511, in error
    result = self._call_chain(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 451, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.3/urllib/request.py", line 686, in http_error_302
    self.inf_msg + msg, headers, fp)
urllib.error.HTTPError: HTTP Error 302: The HTTP server returned a redirect error that would lead to an infinite loop.
The last 30x error message was:
Found

My question is: why is it happening and how can I avoid it?

Thanks in advance.