lending.py: Add logging to exceptions

[cclauss]

Fix. openlibrary/core/lending.py contains many bare exceptions which make it difficult to spot the problems that are causing pytest openlibrary/plugins/openlibrary/tests/test_home.py to fail on Python 3. This PR logs the exceptions in lending.py using
https://docs.python.org/3/library/logging.html#logging.Logger.exception

Technical

Testing

Yes.

Evidence

Stakeholders

[cdrini]

Some questions about some of the new non-exception logs; otherwise lgtm.

[cdrini]

Could you resolve the conflicts on this branch? I tried to but I can't quite figure out what it's supposed to be; it looks like there were some big changes in the test-py3 file. Otherwise code lgtm; I just need to toss on dev to test borrowing 👍

[cdrini]

Tested borrowing works from homepage; lgtm!

Also tested https://openlibrary.org/account/loans works, and return book works.

[cdrini]

Already seeing some errors logged!

Traceback (most recent call last):
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/openlibrary/core/lending.py", line 245, in get_availability
    content = urllib.request.urlopen(url=url, timeout=config_http_request_timeout).read()
  File "/usr/lib/python2.7/urllib2.py", line 127, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.7/urllib2.py", line 410, in open
    response = meth(req, response)
  File "/usr/lib/python2.7/urllib2.py", line 523, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.7/urllib2.py", line 448, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.7/urllib2.py", line 382, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 531, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
HTTPError: HTTP Error 404: Not Found
2020-04-17 14:32:29 [28818] [openlibrary.core.lending] [ERROR] get_available([])
Traceback (most recent call last):
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/openlibrary/core/lending.py", line 216, in get_available
    request = urllib.request.Request(url=url)
  File "/usr/lib/python2.7/urllib2.py", line 202, in __init__
    self.__original = unwrap(url)
  File "/usr/lib/python2.7/urllib.py", line 1060, in unwrap
    url = url.strip()
AttributeError: 'list' object has no attribute 'strip'
2020-04-17 14:32:29 [28818] [openlibrary.core.lending] [ERROR] get_available([])
Traceback (most recent call last):
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/openlibrary/core/lending.py", line 216, in get_available
    request = urllib.request.Request(url=url)
  File "/usr/lib/python2.7/urllib2.py", line 202, in __init__
    self.__original = unwrap(url)
  File "/usr/lib/python2.7/urllib.py", line 1060, in unwrap
    url = url.strip()

[cdrini]

Note to self (and @mekarpeles ); let's keep on eye on this during deploy to make sure it doesn't explode the size of our log files.

[cclauss]

2020-04-17 14:32:29 [28818] [openlibrary.core.lending] [ERROR] get_available([])

url is an empty list! Wrong datatype and no content. A posterchild for bare exceptions.

[cclauss]

https://github.com/internetarchive/openlibrary/blob/master/openlibrary/core/lending.py#L165-L166 is the problem because compose_ia_url() is supposed to return a url (str) but the code here is returning an empty list. Need those Python 3 type hints ;-)

[cclauss]

Were there many of these in the logs? How do we hunt down why this is happening?