Dynamically modifying a form widget in Django

Question

My Django app uses Django Suit as a tool to theme the admin app of Django. One of the things Suit can do is append and prepend elements to form widgets like:

class PropertyForm(ModelForm):
    class Meta:
        model = Property
        widgets = {
            'amount': EnclosedInput(prepend = "GBP"),
        }

The effect is:

Although this is a nice feature it would be more useful if I could add it dynamically like (in pseudo code):

'amount': EnclosedInput(prepend = my_model_instance.currency)

I tried to override the form's init like so:

class PropertyForm(ModelForm):

    def __init__(self, *args, **kwargs):
        inst = kwargs["instance"]
        self._meta.widgets["amount"] = EnclosedInput(prepend = inst.currency)
        super(PropertyForm, self).__init__(*args, **kwargs)

Strangely that only works when I put a breakpoint in the init method. It looks like there's some timing issue involved.

So my question is what would be the best way (if one at all available) to implement this?

Answer 1

The problem is with:

self._meta.widgets["amount"] = EnclosedInput(prepend = inst.currency)

It turns out _meta is being cached. When I change the above line to (which also a nicer solution as _meta is probably private):

self.fields['amount'].widget = EnclosedInput(prepend = inst.currency)

...it works flawlessly