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Saturday, October 10, 2015
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Hamza is working on :ticket:`38`, and I try to have a look at where he
is stuck::

    $ virtualenv django18
    New python executable in django18/bin/python
    Installing setuptools, pip...done.
    $ . django18/bin/activate

    $ pip install django
    Downloading/unpacking django
      Downloading Django-1.8.5-py2.py3-none-any.whl (6.2MB): 6.2MB downloaded
      Storing download in cache at ...
    Installing collected packages: django
    Successfully installed django
    Cleaning up...

Note: I first tried with the preview of 1.9a of Django::

    $ pip install --pre django
    Downloading/unpacking django
      Downloading Django-1.9a1-py2.py3-none-any.whl (6.4MB): 6.4MB downloaded

But this caused an `ImportError` when trying to import from
`django.utils.importlib`. I guess that's because `importlib` is no
longer shipped with Django since it is included in Python 2.7. But I
am not going to fix this now since it is more urgent to get it running
with Django 1.8. We leave 1.9 support for a later ticket.

As Hamza reported earlier: :cmd:`fab initdb` works. That's already a
cool thing.

But then :cmd:`fab initdb` indeed fails with a lot of
`AppRegistryNotReady` exceptions::

    AppRegistryNotReady: The translation infrastructure cannot be
    initialized before the apps registry is ready. Check that you
    don't make non-lazy gettext calls at import time.

Hamza, I have seen this problem before (when trying with 1.7 or 1.8)
and it has a simple explanation: Django has become more severe about
using the translation framework. Officially it was always documented
that nobaody should to non-lazy gettext calls as long as models are
not imported. But Django 1.6. did not check it seriously. So these
problems are either because Lino actually sometimes *does* non-lazy
gettext calls. And in these cases Django is right, we must replace
them by lazy calls.  OTOH the same error can simply be caused by the
fact that `django.setup()` has not been called.

How to proceed. 

First we pick one of the failing tests, e.g. the last one::

    File "lino/utils/ssin.py", line 59, in ssin
    Failed example:
        is_valid_ssin('123')
    Exception raised:

If you look at :file:`tests/__init__.py`, you can deduce that you can
run only this test by executing::

  $ python setup.py test -s tests.UtilsTests.test_ssin

Here is one of the two tracebacks that occur during this test::

    File "lino/utils/ssin.py", line 59, in ssin
    Failed example:
        is_valid_ssin('123')
    Exception raised:
        Traceback (most recent call last):
          File "/usr/lib/python2.7/doctest.py", line 1315, in __run
            compileflags, 1) in test.globs
          File "<doctest ssin[1]>", line 1, in <module>
            is_valid_ssin('123')
          File "lino/utils/ssin.py", line 174, in is_valid_ssin
            ssin_validator(ssin)
          File "lino/utils/ssin.py", line 252, in ssin_validator
            force_unicode(_('Invalid SSIN %s : ') % ssin)
          File "/site-packages/django/utils/functional.py", line 178, in __mod__
            return six.text_type(self) % rhs
          File "/site-packages/django/utils/functional.py", line 140, in __text_cast
            return func(*self.__args, **self.__kw)
          File "/site-packages/django/utils/translation/__init__.py", line 84, in ugettext
            return _trans.ugettext(message)
          File "/site-packages/django/utils/translation/trans_real.py", line 327, in ugettext
            return do_translate(message, 'ugettext')
          File "/site-packages/django/utils/translation/trans_real.py", line 304, in do_translate
            _default = _default or translation(settings.LANGUAGE_CODE)
          File "/site-packages/django/utils/translation/trans_real.py", line 206, in translation
            _translations[language] = DjangoTranslation(language)
          File "/site-packages/django/utils/translation/trans_real.py", line 116, in __init__
            self._add_installed_apps_translations()
          File "/site-packages/django/utils/translation/trans_real.py", line 164, in _add_installed_apps_translations
            "The translation infrastructure cannot be initialized before the "
        AppRegistryNotReady: The translation infrastructure cannot be initialized before the apps registry is ready. Check that you don't make non-lazy gettext calls at import time.

If you now look at the source code of :mod:`lino.utils.ssin`, I see
that we do correctly use a lazy call. The problem here is indeed
"only" that `django.setup()` has not been called. And as you noted
already earlier, you can get the test to pass by adding two lines at
the beginning of the docstring of :mod:`lino.utils.ssin`:

>>> import django
>>> django.setup()

Which confirms that we "only" need to find out how to get this called
automatically.

And yes, the solution has to do with Django's new App Registry, which
is introduced by Andrew Pinkham's `Part III: Django 1.7's New Features
<http://andrewsforge.com/article/upgrading-django-to-17/part-3-django-17-new-features/#app-registry>`_

One commit failed on drone.io and Travis because I forgot to set
`install_requires` becak to `'django<1.7'`.