[Django]-Django 1.7.1 Makemigrations fails when using lambda as default for attribute

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57👍

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The migrations documentation addresses this:

Migrations are just Python files containing the old definitions of your models – thus, to write them, Django must take the current state of your models and serialize them out into a file. While Django can serialize most things, there are some things that we just can’t serialize out into a valid Python representation….

Django can serialize the following: Any function or method reference… in module’s top-level scope

Django cannot serialize: Lambdas

So the solution is simple: instead of a lambda, define a regular function and refer to it by name.

def one_day_hence():
    return datetime.utcnow() + timezone.timedelta(days=1)

class MyModel(models.Model):
    y = models.DateTimeField(default=one_day_hence)
👤Kevin Christopher Henry

1👍

I got the same error below:

ValueError: Cannot serialize function <built-in method date of datetime.datetime object at 0x0000019D077B70F0>: No module

When I set timezone.now().date to DateField() as a default value as shown below:

# "models.py"

from django.db import models
from django.utils import timezone

class MyModel(models.Model):              # Error      
    date = models.DateField(default=timezone.now().date)

So, I set current_date without () which returns timezone.now().date() to DateField() as a default value as shown below, then the error was solved:

# "models.py"

from django.db import models
from django.utils import timezone

def current_date(): # Here
    return timezone.now().date()

class MyModel(models.Model):        # Here      
    date = models.DateField(default=current_date)

Be careful, I can set timezone.now().date() with () to DateField() as a default value without error as shown below, but the default date becomes when the Django server starts (Unchanged):

# "models.py"

from django.db import models
from django.utils import timezone

class MyModel(models.Model):                    # Here ↓↓      
    date = models.DateField(default=timezone.now().date())

In addition, I don’t recommend to use DateField() and TimeField() because they don’t work with TIME_ZONE in settings.py as I asked the question while DateTimeField() does.

👤Super Kai – Kazuya Ito

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