Question

I want my forms to be dynamic, some parameters sucj as max_length for IntegerField varies from model to model. By using the information from here, I have written this form:

def my_form(inputname, inputlastname, inputamount):
 class MyForm(forms.Form):
  name = forms.CharField(max_length=50,required=True,initial=inputname)
  lastname = forms.CharField(max_length=50, required=True,initial=inputlastname)
  amount= forms.IntegerField(max_value=inputamount, required=True)
 return MyForm

It renders well at the template when I call it like this and pass to the template:

form = my_form("David","Bowie",4)()

However I can’t figure out how can I validate it, this fails:

if request.method == ‘POST’:
form = MyForm(request.POST)
if form.is_valid()

Answer 1

There’s no reason to do it this way. You’re making things unnecessarily complicated.

Instead of passing the initial values to a factory function which returns a class with those pre-defined, leave out the initial parameters in the form definition, and pass them in during form instantiation:

class MyForm(forms.Form):
    name = forms.CharField(max_length=50,required=True)
    lastname = forms.CharField(max_length=50, required=True)

…

form = MyForm(request.POST, initial={'firstname':myfirstname, 'surname':mysurname})

Edited after additional question

In order to have a dynamic max_value for amount, you can override the form’s __init__ method and set it there. Then once again you would pass the value in on instantiation.

class MyForm(forms.Form):
    name = forms.CharField(max_length=50,required=True)
    lastname = forms.CharField(max_length=50, required=True)
    amount = forms.IntegerField(required=True)

    def __init__(self, *args, **kwargs):
        amount_max = kwargs.pop('amount_max', None)
        super(MyForm, self).__init__(*args, **kwargs)
        if amount_max:
            self.fields['amount'].max_value = amount_max

…

form = MyForm(request.POST, amount_max=10,
              initial={'firstname':myfirstname, 'surname':mysurname})