Validating a form with overloaded _init_

Question

I have a form with a new init method, which allow to display various choices according to a parameter :

class Isochrone_Set_Parameters(forms.Form):
    Grid_Choices = Grids_Selection.Grid_Choices

    def __init__(self, Grid_Type, *args, **kwargs):
        super(Isochrone_Set_Parameters, self).__init__(*args, **kwargs)

        if Grid_Type == Grids_Selection.Grid_Values[0]:
            Choices = (('0.0','0.0'),('0.1','0.1'),('0.3','0.3'),('0.5','0.5'),('0.6','0.6'),('0.7','0.7'), \
                   ('0.8','0.8'),('0.9','0.9'),('0.95','0.95'))
            self.fields['Rotation_Rate'] = forms.ChoiceField(choices=Choices)
        elif Grid_Type == Grids_Selection.Grid_Values[1]:
            Choices = (('0.0','0.0'),('0.568','0.568'))
            self.fields['Rotation_Rate'] = forms.ChoiceField(choices=Choices)
        else:
            Choices = (('-1.0','-1.0'),('-2.0','-2.0'))
            self.fields['Rotation_Rate'] = forms.ChoiceField(choices=Choices)

        self.fields.keyOrder = [
            'Selected_Grid',
            'Metallicity',
            'Mass',
            'Rotation_Rate']

    Selected_Grid = forms.ChoiceField(choices=Grid_Choices)
    Metallicity = forms.FloatField()
    Mass = forms.FloatField()

and the following view :

def Isochrone(request):
    if request.method == 'POST':# If the form has been submitted...
        form = Isochrone_Set_Parameters(request.POST) # A form bound to the POST data

        if form.is_valid():

            return HttpResponse("C'est ok")

        else:
            return render_to_response("Site/Isochrone.html",{                         
                            'form': form
                            },context_instance=RequestContext(request))
    else:

        form = Isochrone_Set_Parameters(Grid_Type = "NotSet",initial={'Metallicity': -1.0, 'Mass': -1.0, 'Rotation_Rate': -1.0}) # An unbound form

        return render_to_response("Site/Isochrone.html",{
                        'form': form
                        },context_instance=RequestContext(request))

When the form is posted, the form.is_valid() test failed. I have no error messages, and the posted value are accessible through form.POST.["My_Value"]. I don't understand what I am doing wrong. Can somebody give me a hint on how to correct this ?

(I precise that the error seems to be linked to the overloading of the init method in the form, because if I put a simple ChoiceField for Rotation_Rate, it works perfectly.)

Thanks !

Answer 1

You've changed the signature to the form initialization, so that the first parameters is now Grid_Type rather than the usual data. This means that when you do form = Isochrone_Set_Parameters(request.POST), the POST is being used for Grid_Type.

Either make sure you always pass Grid_Type, or (preferably) don't put that in the parameter list at all: get it from kwargs:

def __init__(self, *args, **kwargs):
    Grid_Type = kwargs.pop('Grid_Type', None)
    super(Isochrone_Set_Parameters, self).__init__(*args, **kwargs)
    ...

(Also, please use PEP8-standard naming conventions: IsochroneSetParameters, grid_type, etc).