What on earth is causing this "naive datetime" warning?

[Daniel Grace]

Hi,

Here is my model:

class Flow(models.Model):

    ref = models.CharField(max_length=32)

    state = models.ForeignKey(State)

    flow_type = models.ForeignKey(Type)

    created = models.DateTimeField(db_index=True, auto_now_add=True)

    modified = models.DateTimeField(db_index=True, auto_now=True)

    version = models.IntegerField()

    def __str__(self):

        return str(self.id)

Here is my test.py file:

import warnings

warnings.filterwarnings(

    'error', r"DateTimeField .* received a naive datetime",

    RuntimeWarning, r'django\.db\.models\.fields')

In settings.py:

TIME_ZONE = 'Europe/London'

USE_TZ = True

Here is what happens when I run the test script:

>python manage.py test flow

Creating test database for alias 'default'...

Traceback (most recent call last):

  File "manage.py", line 10, in <module>

    execute_from_command_line(sys.argv)

  File "C:\landy\lib\site-packages\django\core\management\__init__.py", line 385

, in execute_from_command_line

    utility.execute()

  File "C:\landy\lib\site-packages\django\core\management\__init__.py", line 377

, in execute

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

  File "C:\landy\lib\site-packages\django\core\management\commands\test.py", lin

e 50, in run_from_argv

    super(Command, self).run_from_argv(argv)

  File "C:\landy\lib\site-packages\django\core\management\base.py", line 288, in

 run_from_argv

    self.execute(*args, **options.__dict__)

  File "C:\landy\lib\site-packages\django\core\management\commands\test.py", lin

e 71, in execute

    super(Command, self).execute(*args, **options)

  File "C:\landy\lib\site-packages\django\core\management\base.py", line 338, in

 execute

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

  File "C:\landy\lib\site-packages\django\core\management\commands\test.py", lin

e 88, in handle

    failures = test_runner.run_tests(test_labels)

  File "C:\landy\lib\site-packages\django\test\runner.py", line 147, in run_test

s

    old_config = self.setup_databases()

  File "C:\landy\lib\site-packages\django\test\runner.py", line 109, in setup_da

tabases

    return setup_databases(self.verbosity, self.interactive, **kwargs)

  File "C:\landy\lib\site-packages\django\test\runner.py", line 299, in setup_da

tabases

    serialize=connection.settings_dict.get("TEST_SERIALIZE", True),

  File "C:\landy\lib\site-packages\django\db\backends\creation.py", line 374, in

 create_test_db

    test_flush=True,

  File "C:\landy\lib\site-packages\django\core\management\__init__.py", line 115

, in call_command

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

  File "C:\landy\lib\site-packages\django\core\management\base.py", line 338, in

 execute

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

  File "C:\landy\lib\site-packages\django\core\management\commands\migrate.py",

line 160, in handle

    executor.migrate(targets, plan, fake=options.get("fake", False))

  File "C:\landy\lib\site-packages\django\db\migrations\executor.py", line 63, i

n migrate

    self.apply_migration(migration, fake=fake)

  File "C:\landy\lib\site-packages\django\db\migrations\executor.py", line 97, i

n apply_migration

    migration.apply(project_state, schema_editor)

  File "C:\landy\lib\site-packages\django\db\migrations\migration.py", line 107,

 in apply

    operation.database_forwards(self.app_label, schema_editor, project_state, ne

w_state)

  File "C:\landy\lib\site-packages\django\db\migrations\operations\fields.py", l

ine 131, in database_forwards

    schema_editor.alter_field(from_model, from_field, to_field)

  File "C:\landy\lib\site-packages\django\db\backends\schema.py", line 509, in a

lter_field

    self._alter_field(model, old_field, new_field, old_type, new_type, old_db_pa

rams, new_db_params, strict)

  File "C:\landy\lib\site-packages\django\db\backends\schema.py", line 612, in _

alter_field

    new_default = self.effective_default(new_field)

  File "C:\landy\lib\site-packages\django\db\backends\schema.py", line 183, in e

ffective_default

    default = field.get_db_prep_save(default, self.connection)

  File "C:\landy\lib\site-packages\django\db\models\fields\__init__.py", line 62

7, in get_db_prep_save

    prepared=False)

  File "C:\landy\lib\site-packages\django\db\models\fields\__init__.py", line 12

86, in get_db_prep_value

    value = self.get_prep_value(value)

  File "C:\landy\lib\site-packages\django\db\models\fields\__init__.py", line 12

78, in get_prep_value

    RuntimeWarning)

RuntimeWarning: DateTimeField Flow.created received a naive datetime (2014-11-19

 12:28:38.831258) while time zone support is active.

What on earth is causing this "naive datetime" warning?

Thanks

[Russell Keith-Magee]

Hi Daniel,

A naïve datetime is a datetime that doesn't have a timezone. If you have USE_TZ=True enabled in your settings file (which is the default for new projects), Django expects you to fully specify datetime objects with a timezone; if you don't, you get the warning you've seen, because the datetime you've provided is ambiguous. Django can guess, but there's no guarantee that the guess will be correct.

The django.utils.timezone package provides a few utilities to convert naïve datetimes to timezone-enabled datetimes. I'd also suggest looking into pytz, which provides a regularly updated database of the world's timezones.

Yours,

Russ Magee %-)

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[Daniel Grace]

I have already installed pytz (2014.17) and I have set USE_TZ=True.  I don't use any naive datetimes in my application.  This error is caused by something that the Django test command is doing automatically, if you look at the traceback you will see that it is something to do with migrations.  I am using Django 1.7.

[Carl Meyer]

Hi Daniel,

What is the default value for your Flow.created field?

Carl

[Daniel Grace]

Hi Carl,

I was not specifying one, so I changed my model and did a "makemigrations" and a "syncdb" :

class Flow(models.Model):

    ref = models.CharField(max_length=32)

    state = models.ForeignKey(State)

    flow_type = models.ForeignKey(Type)

    created = models.DateTimeField(db_index=True, auto_now_add=True, default=timezone.now)

    modified = models.DateTimeField(db_index=True, auto_now=True, default=timezone.now)

    version = models.IntegerField()

But I still get the exact same warning (see my original message in this thread) !

[Carl Meyer]

Hi Daniel,

On 11/19/2014 08:58 AM, Daniel Grace wrote:
> On Wednesday, 19 November 2014 15:11:27 UTC, Carl Meyer wrote:
> On 11/19/2014 08:07 AM, Daniel Grace wrote:
> > I have already installed pytz (2014.17) and I have set
> USE_TZ=True. I
> > don't use any naive datetimes in my application. This error is
> caused
> > by something that the Django test command is doing automatically,
> if you
> > look at the traceback you will see that it is something to do with
> > migrations. I am using Django 1.7.
>
> What is the default value for your Flow.created field?
>

> Hi Carl,
> I was not specifying one, so I changed my model and did a
> "makemigrations" and a "syncdb" :

"syncdb" is a deprecated alias for "migrate" - may as well start getting
used to doing "migrate" instead.

> class Flow(models.Model):
> ref = models.CharField(max_length=32)
> state = models.ForeignKey(State)
> flow_type = models.ForeignKey(Type)
> created = models.DateTimeField(db_index=True, auto_now_add=True,
> default=timezone.now)
> modified = models.DateTimeField(db_index=True, auto_now=True,
> default=timezone.now)
> version = models.IntegerField()
>
> But I still get the exact same warning (see my original message in this
> thread) !

If you have `auto_now_add=True`, then you don't actually want a default
(it won't have any effect).

But based on your traceback, it seems like at some point in the past
when you made a migration, the field might have had a default value
which was a naive datetime. Is that possible?

It might be necessary to look through your existing migrations for this
app to find the culprit.

Carl

[Daniel Grace]

But based on your traceback, it seems like at some point in the past
when you made a migration, the field might have had a default value
which was a naive datetime. Is that possible?

It might be necessary to look through your existing migrations for this
app to find the culprit.

Yes Carl you were right, I cleared out my migrations folder except for the "__init__.py" file and the problem went away.