When building the info manual ('make info' from the docs/ subdir), I get the following error (build happens in a container without networking):

WARNING: Could not fetch remote image: https://travis-ci.org/eerimoq/cantools.svg?branch=master [HTTPSConnectionPool(host='travis-ci.org', port=443): Max retries exceeded with url: /eerimoq/cantools.svg?branch=master (Caused by NewConnectionError('

So that we can setup mypy on CI we need to elliminate all errors. Currently all serious mypy errors are in canmatrix.canmatrix and most of them are bound to float_factory playing with attrs.

The problem is, that mypy currently only undertsand attr converters, if they are named functions. That means NEITHER converter=decimal.Decimal NOR converter=CanId.from_compound_integer.