Built-In callable as a default argument for a Django Field

I have a JSONField that I need to apply a default dictionary to. As per the documentation, I am avoiding passing the mutable dictionary to the default field. This is done by instead passing the copy method to the default argument like such:

default_dict = {'some_key': 'some value'}

class MyModel(models.Model):
    my_field = models.JSONField(default=default_dict.copy)

When applying makemigrations, this is failing because of the following condition in django.db.migrations.serializer.FunctionTypeSerializer:

if self.value.__module__ is None:
    raise ValueError("Cannot serialize function %r: No module" % self.value)

I can get around this by defining a callable that returns a copy, but I think this is adding unnecessary syntax and makes it harder to read:

class ADict(dict):
    def __call__(self):
        return self.copy()

default_dict = ADict({'some_key': 'some value'})

class MyModel(models.Model):
    my_field = models.JSONField(default=default_dict)

Is there a way to pass a built-in objects method as the default value for a Django field?

Solution

You can't do this since it basically needs to be a named function, whereas default_dict.copy is an "anonymous" function.

You can however make a named function like:

default_dict = {'some_key': 'some value'}

def copy_default_dict():
    return default_dict.copy()

class MyModel(models.Model):
    my_field = models.JSONField(default=copy_default_dict)

or even simpler:

def copy_default_dict():
    return {'some_key': 'some value'}

class MyModel(models.Model):
    my_field = models.JSONField(default=copy_default_dict)