This highlights that the FileHandler class can also be seen as a method
similar to open, and it removes unnecessary context managers, allowing
plugins to close files as they wish (they must, however, remember to
close the file for it to be committed).
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).
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