This removes the assertions that checked plugin devs didn't do anything
overly bad in favour of using mypy to ensure appropriate type-checking.
It also moves the ProgressCallback typing information to constants in
order to avoid circular imports (since constants doesn't import
anything).
Since we stack using Mac layers as well as Linux layers, both sets of
banner caches are required. As the cache builders are separate at the
moment, we previously ran banner searches without any banners. This was
bad. It inflated memory hugely and killed the buildbot.
We now bomb out on stacking a Linux or Mac layer unless we have banners
against which to match.
So that we don't get contributions that include author lines remove any
that exist currently in the code. We need to figure out how we're going
to support attribution, probably through an AUTHORS file, but definitely
not peppering the code.
This includes:
* Better ways of checking empty lists
* Not shadowing builtin functions like filter
* Preventing invalid slash warnings by marking strings as regexps
* Removing unnecessary brackets
* Lowercase variable names
* Adding/updating parameters in docstrings
* Removing unused code (lines not chunks)
* Change in not a member tests
* Changing some methods to static
* Shorting range membership checks
* Missing parameters
* Make some exception handlers more specific
* Don't define a lambda to a variable
* A few more instance checks to help type checkers
Relented on the strict import of direct objects/classes for the typing
module only. Typing module components can be directly imported because
it makes the code really painful to read and write otherwise.
This is still in-line with the python style guide adopted from Google at
http://google.github.io/styleguide/pyguide.html section 2.2.
Mike Auty