:date: 2017-12-15

=========================
Friday, December 15, 2017
=========================


AmbiguousTimeError
==================

Yesterday Tonis and I had a surprise during an otherwise routine
upgrade on Jane.  We called it :ticket:`2204`.

Today we found out how to reproduce the problem and eliminate its
cause.  Thanks to Ilian Iliev for publishing his blog post `Django,
pytz, NonExistentTimeError and AmbiguousTimeError
<http://www.ilian.io/django-pytz-nonexistenttimeerror-and-ambiguoustimeerror/>`__.

When somebody living in Brussels tells you "it was at on 2017-10-29 at
01:16:06", then you don't know whether they mean summer or winter
time.  Because their clock showed that time exactly twice during that
night. The timestamp "2017-10-29 01:16:06" is ambigous.

The reason for :ticket:`2204` was that :cmd:`pm dump2py` used the
site's default :setting:`TIME_ZONE` setting when writing the naive
values of DateTimeFields in the generated `applabel_modelname.py`
files.  When trying to load a dump which contains such a timstamp,
Lino would cause an `AmbiguousTimeError`.

So :cmd:`pm dump2py` must make sure to express the naive time literals
in a timezone which doesn't have such ambigous hours. UTC for example.

I extended :ref:`book.specs.dumps` so that it now verifies whether
:ticket:`2204` is fixed.  En passant this page now also demonstrates
three methods of writing demo multilingual data for babel fields.


Authenticate using Facebook
===========================

I added Facebook as a **third authentication backend** to the
:mod:`lino_book.projects.team` demo project and updated the
:ref:`lino.socialauth` page.

Before doing this, **I reappeared on Facebook** after :doc:`two years of absence
<../2015/1104>` (not two and a half, as I first thought when writing this).  Oh
no, it's not because I have become their friend.  It's rather because having no
Facebook account while continuing to have a Google account is even worse than
having a FB account as well.  Both Facebook and Google are huge powerful
imperia, and every user is another buttress of their power.  That's a  `big
problem <http://hw.saffre-rumma.net/big_egoists.html>`__ because organizations
of that size should be democratic and open instead of hierarchic and
proprietary.  But it's also clear that I won't save the world by keeping out of
them...