Django/Python - Check if argument was passed to class

Question

I am passing different arguments to a Django form and would like check which argument was passed inside the form's class. How can i do that?

views.py

...
form = CategoryForm(choose_category =True)
...

forms.py

class CategoryForm(forms.Form):

    def __init__(self, *args, **kwargs):

        self.choose_category = kwargs.pop('choose_category',None)
        super(CategoryForm,self).__init__(*args, **kwargs)
        self.helper = FormHelper()
        self.helper.form_method = 'POST'

        if not self.choose_category:
            self.helper.add_input(Submit('submit', 'Submit', css_class='btn-success'))

    if self.choose_category:
        do something

In the example above- the error is that name 'self' is not defined , how can i check for the existence of choose_category outside of __init__ ?

This is rather a question of python, how can i check which parameters have been passed to a class from inside the class but outside of the __init__ constructor. Also an answer such as - you cannot, it's stupid - is welcome if i get to understand the logical fracture i'm making:)

Thank you!

EDIT: forms. py

Can't understand why this does not work and the fields don't display:

class CategoryForm(forms.Form)

    def __init__(self, *args, **kwargs):

        self.choose_category = kwargs.pop('choose_category',None)
        super(CategoryForm,self).__init__(*args, **kwargs)
        self.helper = FormHelper()
        self.helper.form_method = 'POST'

        if not self.choose_category:

            self.helper.add_input(Submit('submit', 'Submit', css_class='btn-success'))
            self.onchange(False)
        else:
            self.onchange(True)

    def onchange (self, val):

        if val:
            category = forms.ModelChoiceField(
                queryset =Categories.objects.all(),
                widget = forms.Select(attrs = {'onchange':'form.submit();'}) ,
                empty_label= None,
                required=True
                )
            print('why doesnt it work this way')
        else:
            category = forms.ModelChoiceField(queryset =Categories.objects.all() ,empty_label= None,required=True)

Answer 1

This sort of thing has to be done inside __init__ . From there you can add or modify field definitions via the self.fields dict.

if choose_category:
    self.fields['cat'] = forms.ModelChoiceField(queryset=....)