an idea on persisting redirect history when exceptions are encountered

[jvanasco]

this is a quick idea on an approach to address #4455

within resolve_redirects exceptions raised bySession.send are caught. If they match a given set of tests (currently just the base ConnectionError class), the resp is replaced with an instance of an exception class used to hold bad response data. Then a new exception is raised.

This makes handling these types of errors similar to handling items without redirects for most users (i did not consider the legacy ways of using requests)

The immediate ideas/concerns I have on this:

1. It might make sense to have a global "NotARealResponse" object that stands in for a Response object and can contain connection/history info when there is no immediate response. I'm not sure this is the only use-case for this.

2. I thought about extending the current exception with request/response data, but this seemed more appropriate.

Just to be clear, this is only submitted for discussion/illustration of the other ticket. This is not a PR for merging.

[codecov-io]

Codecov Report

Merging #4456 into master will decrease coverage by 0.25%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #4456      +/-   ##
==========================================
- Coverage   90.14%   89.89%   -0.26%     
==========================================
  Files          15       15              
  Lines        1543     1554      +11     
==========================================
+ Hits         1391     1397       +6     
- Misses        152      157       +5

Impacted Files	Coverage Δ
requests/sessions.py	93.95% <66.66%> (-1.61%)	:arrow_down:

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