API server code health pass - rework parse* & extract* methods

[rzats]

Partially addresses #998.

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

Summary

Fixes a set of issues in the server code as described here.

• Moves parse_* and extract_* methods to params.py instead of validate.py.
• Also does the same with several methods from covidcast.py.
• Also renames the methods to more accurately represent their purpose (pending some discussion with George)

[melange396]

This looks pretty good, but out of curiousity: Did you do a straight copy of the 11 methods moved to _params.py from _validate.py and covidcast.py, or did you make changes to them? Similarly, any changes in the test methods moved from test_validate.py to test_params.py? I presume there are no such changes, but i cant easily tell from the diffs shown by github.

...

also, optionally:

(if you dont want to do the following stuff now, its not a problem -- i will just put these comments into #998 for a future pass)

It would be nice if [for now] the only places request is used as an import is in _params.py (which is specifically used to get "parameters" from a "request"), in endpoints (which each legitimately process a "request"), in main.py (which is effectively an endpoint itself), and in _common.py (which uses it in the context of pre- and post-request app decorators)... To that end, can we:

• make the methods left in _validate.py take request as a function argument instead of as an import?
• change print_non_standard() and create_printer() in _printer.py to take format as an argument instead of pulling it from the imported request?

...which leaves _exceptions.py, where the constructor for EpiDataException uses request in a hacky special-cased compatibility workaround. The subclasses of the exception make use of it too. We can leave that one alone [for now].

[melange396]

you can remove parens and newlines since this is now a single import

[rzats]

@melange396 fixed some merge conflicts and your comment, so the PR should be good to review again!

Regarding your followup questions:

• The methods are moved as-is, no changes there.
• The request changes are actually within the scope of this pass (AKA, to be done this week) and in fact mostly finished in a local branch; I'd just like to put them in a separate PR after this one is merged.

[melange396]

looks good, we will just need to remember to refer to my comment above regarding request as an argument (in the subsequent PR)