Add compat function for date.fromisocalendar for Python 3.6-3.7

src/pretix/helpers/compat.py

@@ -0,0 +1,9 @@
+import datetime
+import sys
+
+
+def date_fromisocalendar(isoyear, isoweek, isoday):
+    if sys.version_info < (3, 8):
+        return datetime.datetime.strptime(f'{isoyear}-W{isoweek}-{isoday}', "%G-W%V-%u")
+    else:
+        return datetime.datetime.fromisocalendar(isoyear, isoweek, isoday)

src/pretix/presale/views/event.py

@@ -29,6 +29,7 @@ from pretix.base.models.items import (
     ItemBundle, SubEventItem, SubEventItemVariation,
 )
 from pretix.base.services.quotas import QuotaAvailability
+from pretix.helpers.compat import date_fromisocalendar
 from pretix.multidomain.urlreverse import eventreverse
 from pretix.presale.ical import get_ical
 from pretix.presale.signals import item_description
@@ -466,7 +467,7 @@ class EventIndex(EventViewMixin, EventListMixin, CartMixin, TemplateView):
             ) < 2
             context['days'] = days_for_template(ebd, week)
             context['weeks'] = [
-                (date.fromisocalendar(self.year, i + 1, 1), date.fromisocalendar(self.year, i + 1, 7))
+                (date_fromisocalendar(self.year, i + 1, 1), date_fromisocalendar(self.year, i + 1, 7))
                 for i in range(53 if date(self.year, 12, 31).isocalendar()[1] == 53 else 52)
             ]
             context['years'] = range(now().year - 2, now().year + 3)

src/pretix/presale/views/organizer.py

@@ -21,6 +21,7 @@ from pretix.base.models import (
     Event, EventMetaValue, SubEvent, SubEventMetaValue,
 )
 from pretix.base.services.quotas import QuotaAvailability
+from pretix.helpers.compat import date_fromisocalendar
 from pretix.helpers.daterange import daterange
 from pretix.helpers.formats.de.formats import WEEK_FORMAT
 from pretix.multidomain.urlreverse import eventreverse
@@ -524,7 +525,7 @@ class WeekCalendarView(OrganizerViewMixin, EventListMixin, TemplateView):
 
         ctx['days'] = days_for_template(ebd, week)
         ctx['weeks'] = [
-            (date.fromisocalendar(self.year, i + 1, 1), date.fromisocalendar(self.year, i + 1, 7))
+            (date_fromisocalendar(self.year, i + 1, 1), date_fromisocalendar(self.year, i + 1, 7))
             for i in range(53 if date(self.year, 12, 31).isocalendar()[1] == 53 else 52)
         ]
         ctx['years'] = range(now().year - 2, now().year + 3)