When running pm prep in team with py2 and django 1.11.8 the following error occurs.

Updating summary data for Tickets ...

Traceback (most recent call last):

 File "manage.py", line 9, in <module>

   execute_from_command_line(sys.argv)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line

   utility.execute()

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 356, in execute

   self.fetch_command(subcommand).run_from_argv(self.argv)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/base.py", line 283, in run_from_argv

   self.execute(*args, **cmd_options)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute

   output = self.handle(*args, **options)

 File "/home/tonis/Projects/lino/src/lino/lino/management/commands/prep.py", line 45, in handle

   super(Command, self).handle(**options)

 File "/home/tonis/Projects/lino/src/lino/lino/management/commands/initdb.py", line 241, in handle

   call_command('loaddata', *fixtures, **options)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 131, in call_command

   return command.execute(*args, **defaults)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute

   output = self.handle(*args, **options)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/commands/loaddata.py", line 69, in handle

   self.loaddata(fixture_labels)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/commands/loaddata.py", line 109, in loaddata

   self.load_label(fixture_label)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/commands/loaddata.py", line 166, in load_label

   for obj in objects:

 File "/home/tonis/Projects/lino/src/lino/lino/utils/dpy.py", line 415, in deserialize

   for o in self.deserialize_module(module, **options):

 File "/home/tonis/Projects/lino/src/lino/lino/utils/dpy.py", line 429, in deserialize_module

   for obj in objects():

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/fixtures/checksummaries.py", line 12, in objects

   call_command('checksummaries')

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 131, in call_command

   return command.execute(*args, **defaults)

 File "/home/tonis/Projects/lino/2.7/local/lib/python2.7/site-packages/django/core/management/base.py", line 330, in execute

   output = self.handle(*args, **options)

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/management/commands/checksummaries.py", line 29, in handle

   ses.run(settings.SITE.site_config.check_all_summaries)

 File "/home/tonis/Projects/lino/src/lino/lino/core/requests.py", line 648, in run

   return ia.run_from_session(self, *args, **kw)

 File "/home/tonis/Projects/lino/src/lino/lino/core/requests.py", line 1379, in run_from_session

   self.bound_action.action.run_from_code(ar)

 File "/home/tonis/Projects/lino/src/lino/lino/core/actions.py", line 751, in run_from_code

   self.run_from_ui(ar, *args, **kwargs)

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/models.py", line 20, in run_from_ui

   sm.check_all_summaries()

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/mixins.py", line 58, in check_all_summaries

   cls.update_for_filter()

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/mixins.py", line 63, in update_for_filter

   obj.compute_summary_values()

 File "/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/mixins.py", line 87, in compute_summary_values

   collector(obj)

 File "/home/tonis/Projects/lino/src/noi/lino_noi/lib/tickets/models.py", line 110, in add_from_session

   value = getattr(self, k) + d

 File "/home/tonis/Projects/lino/src/lino/lino/utils/quantities.py", line 82, in __add__

   return self.__class__(Decimal.__add__(self, *args, **kw))

 File "/home/tonis/Projects/lino/src/lino/lino/utils/quantities.py", line 198, in __new__

   self = Decimal.__new__(Duration, value, context)

 File "/usr/lib/python2.7/decimal.py", line 657, in __new__

   raise TypeError("Cannot convert %r to Decimal" % value)

TypeError: Problem installing fixture '/home/tonis/Projects/lino/src/lino/lino/modlib/summaries/fixtures/checksummaries.py': Cannot convert NotImplemented to Decimal