Use getattr rather than direct __dict__ access

Mirror what we're doing when setting the attributes.
Improve data coverage algorithm

Data that was not requested should not be included in the data coverage
algorithm.

[Fixes #55970986]
Tidy up a couple of pep8 violations
pep8

Removing the trailing space to match the removed leading space.
Merge pull request #88 from alphagov/data-coverage-bug

Data coverage bug