* HTTP Handler class annotations for py2/urllib2 & py3/urllib.request
Add full annotations for the following classes:
* Python 2:
* `urllib2.AbstractHTTPHandler`
* `urllib2.HTTPHandler`
* `urllib2.HTTPsHandler`
* Python 3:
* `urllib.request.AbstractHTTPHandler`
* `urllib.request.HTTPHandler`
* `urllib.request.HTTPsHandler`
This information is largely undocumented, and was obtained by directly examining
the Python source code:
* Python 2 (v2.7.15) - https://github.com/python/cpython/blob/v2.7.15/Lib/urllib2.py#L1115-L1243
* Python 3 (v3.7.1) - https://github.com/python/cpython/blob/v3.7.1/Lib/urllib/request.py#L1224-L1364
`urllib2.AbstractHTTPHandler.do_open` takes as a parameter either
`HTTPConnection` or `HTTPSConnection`--one of the classes, not an instance of
either--and constructs an object using only a few of the parameters that either
constructor could use. `HTTPConnectionProtocol` in `stdlib/2/httplib.pyi`
follows a similar patten to `HTTPConnectionProtocol` added to
`stdlib/3/http/client.pyi` in pull request #2582 to describe the type of the
`http_class` that is passed to `do_open`.
It seems that code using HTTPError previously worked by accident
because we used to accept arbitrary keyword arguments when
instantiating BaseException, or any subclass of BaseException
(see https://github.com/python/typeshed/pull/2348).
This commit adds in the correct constructor (which also lets the
user specify the arguments in keyword-argument form).
Note: I'm not very familiar with the urllib libraries, so I opted
to just add the signature and leave it up to somebody else to
fill in the types.
* Add flags to pass on --warn-unused-ignores and --no-implicit-optional to mypy
* Make implicit Optional explicit in arg types (2and3 part)
* Convert {stdlib,third_party}/2 to explicit Optional
