Reverse look fails when importing from the admin for an app

[Derek]

My pytest suite is currently not working, as the reverse lookup is failing for admin views; for example, trying to access `reverse('admin:myapp_mymodel_changelist')` or `reverse_lazy('admin:myapp_mymodel_changelist')`.

I have narrowed down the cause to the trigger being *any* kind of import being made from the `admin.py` code for that app; the available URLs are still there for all the other apps but *not* for the one being imported.

In `django/urls/resolvers.py` package, the available possible matches are determined here:

    possibilities = self.reverse_dict.getlist(lookup_view)

And one can add a debug statement which shows all the keys:

    keys = [key for key in [*self.reverse_dict] if isinstance(key, str)]
    print(keys)

Some basic test code, which I run in the Django shell, demonstrates how the failure is triggered, and shows that this is not an artefact related to the tests themselves:

    from django.core.urlresolvers import reverse_lazy
    from myapp.admin import MyModelAdmin
    print(reverse_lazy('admin:myapp_mymodel_changelist'))

But this passes:

    from django.core.urlresolvers import reverse_lazy
    print(reverse_lazy('admin:myapp_mymodel_changelist'))

i.e. if I comment out the import line the code works, otherwise it fails.

Any ideas on why Django is failing when importing from the app's admin?

Thanks
Derek