Question

I’d like to have a field which is required conditionally based on setting a boolean value to True or False.

What should I return to set required =True if is_company is set to True?

class SignupFormExtra(SignupForm):
    is_company = fields.BooleanField(label=(u"Is company?"), 
                                     required=False)
    NIP = forms.PLNIPField(label=(u'NIP'), required=False)

    def clean(self):
        if self.cleaned_data.get('is_company', True):
            return ...?
        else:
            pass

Answer 1

Check the Chapter on Cleaning and validating fields that depend on each other in the documentation.

The example given in the documentation can be easily adapted to your scenario:

def clean(self):
    cleaned_data = super(SignupFormExtra, self).clean()
    is_company = cleaned_data.get("is_company")
    nip = cleaned_data.get("NIP")
    if is_company and not nip:
        raise forms.ValidationError("NIP is a required field.")
    return cleaned_data