KeyError: u'blank' or KeyError: u'editable' when upgrading django

[latheef]

Seems this error is oftenly coming when doing makemigrations or migrate commad.

In django 1.8, line is

​https://github.com/django/django/blob/1.8/django/db/models/fields/__init__.py#L1252

        if self.auto_now or self.auto_now_add:
            del kwargs['editable']
            del kwargs['blank']

This is not checking whether field is there or not. Can solve it by

        if self.auto_now or self.auto_now_add:
            if 'editable' in kwargs: del kwargs['editable']
            if 'blank' in kwargs: del kwargs['blank']

After some digging I can see the problem is happening because of deconstruct method in Field class.

The place where above kwargs getting is

        keywords = {}
        possibles = {
            "verbose_name": None,
            "primary_key": False,
            "max_length": None,
            "unique": False,
            "blank": False,
            "null": False,
            "db_index": False,
            "default": NOT_PROVIDED,
            "editable": True,
            "serialize": True,
            "unique_for_date": None,
            "unique_for_month": None,
            "unique_for_year": None,
            "choices": [],
            "help_text": '',
            "db_column": None,
            "db_tablespace": settings.DEFAULT_INDEX_TABLESPACE,
            "auto_created": False,
            "validators": [],
            "error_messages": None,
        }
        attr_overrides = {
            "unique": "_unique",
            "choices": "_choices",
            "error_messages": "_error_messages",
            "validators": "_validators",
            "verbose_name": "_verbose_name",
        }
        equals_comparison = {"choices", "validators", "db_tablespace"}
        for name, default in possibles.items():
            value = getattr(self, attr_overrides.get(name, name))
            # Unroll anything iterable for choices into a concrete list
            if name == "choices" and isinstance(value, collections.Iterable):
                value = list(value)
            # Do correct kind of comparison
            if name in equals_comparison:
                if value != default:
                    keywords[name] = value
            else:
                if value is not default:
                    keywords[name] = value

Here, it is not returning keys editable or blank sometimes based on if condition.Thats why it is happening.

[Tim Graham]

Can you please add steps or a sample project to reproduce the issue?

[latheef]

I got it why this is happening. If override DateField like ​http://ianrolfe.livejournal.com/36017.html

class MyDateField(models.DateField):
    def __init__(self, null=False, blank=False, **kwargs):
        super(MyDateField, self).__init__(**kwargs)
        self.editable = True #This will give key error 'editable'
        self.blank = False #This will give key error 'blank'  

Above code is working for syncdb(older). But this gettings error when makemigrations and migrate command versions of django.

[Tim Graham]

I don't think this is a bug in Django. Please see ​Field deconstruction and use TicketClosingReasons/UseSupportChannels if you need further help.