The relevant test has been updated in git, so it may take a git snapshot to work with python3.5:
https://projects.kde.org/projects/extragear/kdevelop/plugins/kdev-python/repository/revisions/master/entry/parser/CMakeLists.txt
- Bug#810750: kdevelop-python: FTBFS with python3... Scott Kitterman
- Bug#810750: Acknowledgement (kdevelop-pyth... Scott Kitterman
- Bug#810750: marked as done (kdevelop-pytho... Debian Bug Tracking System
