[Python-modules-team] Bug#911771: IPv4: AttributeError: 'module' object has no attribute 'in_' = Missing version constraint on python-attr dependencies

[Ulrike Uhlig]

After some research, this is actually not due to python-twisted but to a
change in the API of python-attrs in 17.1.0
(http://www.attrs.org/en/stable/changelog.html).

But python-twisted from stretch-backports has no versioned dependency on
python-attrs > 17.1.0. Installing python-attrs from stretch-backports
fixes the issue.

#910056 seems to concern the same problem and possibly #911771 should be
merged with it.

Ulrike