We add the flake8 configuration used so we ensure everyone uses the same.
We remove the usage of __all__ for non public API.
When possible, we rationalize the class name according to its __name__ and module.
issue9082
review297061002
We can not rely on the deepcopy of the field because the Mixin maybe added
after the class that define the field. In this case we modify the reference
field for the deepcopy.
issue7434
review47421002
Cédric Krier