Thursday, November 28, 2019

Running Linux on an older PC

Ticket #3357 is not directly related to Lino. I am installing LXLE on Ly’s old notebook computer in order to make it quick again so that Iiris can use it. It had become unbearably slow because it has only 2 GB of RAM, and Ubuntu is simply too fat for this old machine. Quote from a discussion on linux.org : “IMO to have an enjoyable 1st experience using Ubuntu 18.04 LTS or any Linux I would highly recommend at least 4.0 GB of memory. From my experience trying to run Ubuntu 18.04 LTS with only 2.0 GB memory will be painful at best.”

LXLE is a “Full featured OS for an aging PC” based on Lubuntu. I chose it after reading 10 Best Lightweight Linux Distributions For Older Computers.

I downloaded an ISO image from https://sourceforge.net/projects/lxle/

How to get the ISO file to an USB stick? This article suggests that that Startup Disk Creator can do it. I had to install python3-coverage before getting it installed:

$ sudo apt-get install python3-coverage
$ sudo apt install usb-creator-gtk
../../_images/2019-11-28_07-10-55.png

Before it actually starts writing, it asks “Are you sure you want to write to the selected device? All data will be lost.” The operation then takes a few minutes. At the end it says “Installation is complete. You may now run Ubuntu on other computers by booting them with this drive inserted.”

I manually unmounted the USB stick before removing it.

Another article suggests to simply use dd: https://vitux.com/how-to-create-a-bootable-usb-stick-from-the-ubuntu-terminal/

Lino gets ready for Django 3.0

It’s already 10 days ago that they released Django 3.0 release candidate 1. Now I did pip install --pre -U django and ran the test suite. I opened #3360 for this.

  • “TypeError: not all arguments converted during string formatting” in lino when parsing the Django version. Now Lino will work also with Django 4+.

  • ImportError: cannot import name ‘python_2_unicode_compatible’ : so I removed this decorator from everywhere (several hundred occurrences in more than a dozen repositories!)

  • Replaced “from django.utils import six” by “import six”. Started replacing six.text_type() by str() Soon we might also remove all usage of six, but that’s not a blocker.

  • TypeError: ‘NoneType’ object is not iterable : seems that Field.choices can now be None. Okay, why not.

  • TypeError: from_db_value() missing 1 required positional argument: ‘context’ :

    That was because we have several Lino fields that define a from_db_value() method:

    def from_db_value(self, value, expression, connection, context):

    And the Release notes say clearly that “Support for the context argument of Field.from_db_value() and Expression.convert_value() is removed.”

    So I changed the signature of these methods so that they support both Django 2 and 3:

    def from_db_value(self, value, expression, connection, context=None):

  • django.core.exceptions.ValidationError: {‘choicelist’: [“Value ‘properties.HowWell’ is not a valid choice.”]}

    The lino_xl.lib.properties plugin is rather deprecated but still used in Lino Welfare.

    I moved the choicelists into a separate choicelists.py module because I had a feeling that maybe that triggers the problem. Nope. But I leave them in a separate module.

    So what then is happening there? Aha, look at the PropType.choicelist field. It is defined as follows:

    choicelist = models.CharField(
    max_length=50, blank=True,
    verbose_name=_("Choices List"),
    choices=choicelist_choices())

    The lino.core.kernel.choicelist_choices() function returns a sorted list of all choicelists in this application. But: this list is not yet populated when the modules.py modules are being imported. So the return value is always empty. Also in Django 2 this field does not have any choices. Django 3 detected a bug in our code that had gone unnoticed in Django 2 :-)

    The solution is to use a chooser, i.e. a choicelist_choices method. Now it works at least in Django 2.

  • All primary keys had sums in doctests. Lino assumes that the sum of a primary key makes no sense and therefore it is automatically hidden. This logic lives in the lino.core.elems.AutoFieldElement class where we say:

    class AutoFieldElement(NumberFieldElement):

    def value2num(self, v):
        return 0

    The lino.core.elems.field2elem() works by looping over a list of Django database field classes and finds the first element class found for the database field. One thing that’s new in Django 3 : AutoField now inherits from IntegerField. That makes sense, but it caused Lino to return an IntegerFieldelement for AutoField as well. The solution was easy: simply test for AutoField before testing for IntegerField.

Commits: