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Python's enums are not extensible, values can't be added and they can't
be subclassed. This is problematic if weboob devel adds new values,
because stable weboob will not be able to use them. They would need to
be replaced by a default value or None, which loses information.

Instead, implement custom enums that contain plain constants and support
adding values aftewards.

Signed-off-by: Simon Lipp <laiquo@hwold.net>

flake8 --select W391,E302,E301,E304

autopep8 can't fix W391 even though it claims it can.
Fixed using a simple custom script.

Remove useless trailing \
Remove trailing spaces
Add missing empty lines

autopep8 -ir -j2 --select=E301,E302,E502,W291,W293,W391 .

Diff quickly checked.

Modules can raise this exception when they want to print errors to user