How to set the default of a JSONField to empty list in Django and django-jsonfield?

According to the Django documentation for JSONField you should indeed use default=list because using default=[] would create a mutable object that is shared between all instances of your field and could lead to some objects not having an empty list as a default.

Please note that this does not only apply for django.contrib.postgres.fields.JSONField but for all other kinds of objects and functions in Python in general.

Quote from the docs:

If you give the field a default, ensure it’s a callable such as list (for an empty default) or a callable that returns a list (such as a function). Incorrectly using default=[] creates a mutable default that is shared between all instances of

list and dict are callable, while [] and {} are not (you can't do []()). So:

• Use JSONField(default=list) over JSONField(default=[])
• Use JSONField(default=dict) over JSONField(default={})

If you want to instantiate with some data you can do the following:

def jsonfield_default_value():  # This is a callable
    return [0, 0]  # Any serializable Python obj, e.g. `["A", "B"]` or `{"price": 0}`

class MyModel(Model):
    the_list_field = JSONField(default=jsonfield_default_value)