How to inherit from class in same file when generating Django dynamic form

Question

I'm fairly new to both Python and Django, and I'm in the process of building a small website. I've been experimenting with a dynamic form containing a ModelChoiceField constructed from a QuerySet that is determined by user input. The approach described here works well for me, but I run into trouble if I try to dynamically create a type that inherits from a class that I define within the same file. The reason I tried to do this was that I wanted to override the default form field order by setting the form's fields.keyOrder property.

This is how I tried to do it:

from django import forms

class AbstractForm(forms.Form):
    def __init__(self, *args, **kwargs):
        super(AbstractForm, self).__init__(*args, **kwargs)
        self.fields.keyOrder = ['choices', 'second', 'third']

class ConcreteFormFactory(object):
    @staticmethod
    def generate(queryset):
        properties = {
            'second': forms.CharField(),
            'third': forms.CharField(),
            'choices': forms.ModelChoiceField(queryset=queryset)
        }
        return type('ConcreteForm', (AbstractForm,), properties)

However, when I import ConcreteFormFactory in my view and attempt to call its generate() method, I get a NameError telling me that AbstractForm is not defined. I tried importing AbstractForm into the calling context, but to no avail. Since I wasn't able to get this approach to work, I accomplished my goal another way, but I would still like to understand the scoping issue here. How do I make my dynamic class aware of other classes defined in the same file where I create it? This is on Django 1.2 and Python 2.7.1 (I know that's a very old version of Django).

It should work like this. Can you post the traceback of that NameError? — sk1p
– sk1p, Commented Dec 27, 2013 at 0:25
Why have you set generate(queryset) to a static method? This may be the issue as static methods are called differently against the class instead of the instance object. — Furbeenator
– Furbeenator, Commented Dec 27, 2013 at 0:52
But @staticmethod shouldn't change how name lookups are done, right? Something like class A(object): pass, class AFactory(object): @staticmethod def makeA(): return type('A', (A,), {}) works fine for me — sk1p
– sk1p, Commented Dec 27, 2013 at 1:03
Well that figures...I implemented my generic test code that I posted here and it worked. Then I refactored my real code to use this pattern and it worked. I must have had something else wrong. Sorry everybody! — Max Crowe
– Max Crowe, Commented Dec 27, 2013 at 1:06
But did you import it from another module? I didn't try that, but it just seems strange to me. I could be way off base here. — Furbeenator
– Furbeenator, Commented Dec 27, 2013 at 1:07

Max Crowe · Accepted Answer · 2013-12-27 01:10:08Z

1

I apologize--this code DOES work as intended. I refactored my real code to use this pattern, and this time it worked. I must have had something else wrong.

answered Dec 27, 2013 at 1:10

Max Crowe

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2 Comments

Anentropic Over a year ago

please close your question if it is not going to be helpful for others

Max Crowe Over a year ago

Sorry, it won't let me.

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