Open Source Summit: http://events.linuxfoundation.org/events/open-source-summit-...
Euro Python: https://ep2017.europython.eu/en/ (2018 site is not yet, and will be probably somewhere else)
Django Con Europe: https://2018.djangocon.eu/
And many cool local PyCon's, such as PyCon SK 2018: https://2018.pycon.sk/en/index.html
Disclaimer: I am part of the PyCon SK organizational team