Question

I am having trouble understanding how to initialize a custom form field in a django view.

For example: http://djangosnippets.org/snippets/907/

from datetime import date, datetime
from calendar import monthrange

class CreditCardField(forms.IntegerField):
    @staticmethod
    def get_cc_type(number):
        number = str(number)
        #group checking by ascending length of number
        if len(number) == 13:
            if number[0] == "4":
                return "Visa"
        return "Unknown"

    def clean(self, value):
        if value and (len(value) < 13 or len(value) > 16):
            raise forms.ValidationError("Please enter in a valid "+\
                "credit card number.")
        elif self.get_cc_type(value) not in ("Visa", "MasterCard",
                                             "American Express"):
            raise forms.ValidationError("Please enter in a Visa, "+\
                "Master Card, or American Express credit card number.")
        return super(CreditCardField, self).clean(value)

class CCExpWidget(forms.MultiWidget):
    """ Widget containing two select boxes for selecting the month and year"""
    def decompress(self, value):
        return [value.month, value.year] if value else [None, None]

    def format_output(self, rendered_widgets):
        html = u' / '.join(rendered_widgets)
        return u'<span style="white-space: nowrap">%s</span>' % html


class CCExpField(forms.MultiValueField):
    EXP_MONTH = [(x, x) for x in xrange(1, 13)]
    EXP_YEAR = [(x, x) for x in xrange(date.today().year,
                                       date.today().year + 15)]
    default_error_messages = {
        'invalid_month': u'Enter a valid month.',
        'invalid_year': u'Enter a valid year.',
    }

    def __init__(self, *args, **kwargs):
        errors = self.default_error_messages.copy()
        if 'error_messages' in kwargs:
            errors.update(kwargs['error_messages'])
        fields = (
            forms.ChoiceField(choices=self.EXP_MONTH,
                error_messages={'invalid': errors['invalid_month']}),
            forms.ChoiceField(choices=self.EXP_YEAR,
                error_messages={'invalid': errors['invalid_year']}),
        )
        super(CCExpField, self).__init__(fields, *args, **kwargs)
        self.widget = CCExpWidget(widgets =
            [fields[0].widget, fields[1].widget])

    def clean(self, value):
        exp = super(CCExpField, self).clean(value)
        if date.today() > exp:
            raise forms.ValidationError(
            "The expiration date you entered is in the past.")
        return exp

    def compress(self, data_list):
        if data_list:
            if data_list[1] in forms.fields.EMPTY_VALUES:
                error = self.error_messages['invalid_year']
                raise forms.ValidationError(error)
            if data_list[0] in forms.fields.EMPTY_VALUES:
                error = self.error_messages['invalid_month']
                raise forms.ValidationError(error)
            year = int(data_list[1])
            month = int(data_list[0])
            # find last day of the month
            day = monthrange(year, month)[1]
            return date(year, month, day)
        return None


class PaymentForm(forms.Form):
    number = CreditCardField(required = True, label = "Card Number")
    holder = forms.CharField(required = True, label = "Card Holder Name",
        max_length = 60)
    expiration = CCExpField(required = True, label = "Expiration")
    ccv_number = forms.IntegerField(required = True, label = "CCV Number",
        max_value = 9999, widget = forms.TextInput(attrs={'size': '4'}))

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

    def clean(self):
        cleaned = super(PaymentForm, self).clean()
        if not self.errors:
            result = self.process_payment()
            if result and result[0] == 'Card declined':
                raise forms.ValidationError('Your credit card was declined.')
            elif result and result[0] == 'Processing error':
                raise forms.ValidationError(
                    'We encountered the following error while processing '+\
                    'your credit card: '+result[1])
        return cleaned

    def process_payment(self):
        if self.payment_data:
            # don't process payment if payment_data wasn't set
            datadict = self.cleaned_data
            datadict.update(self.payment_data)

            from virtualmerchant import VirtualMerchant
            vmerchant = VirtualMerchant(datadict)

            return vmerchant.process_virtualmerchant_payment()

In the above example payment form, how would you pass initial data to PaymentForm.expiration field?

I know you can do:

c = PaymentForm({'number':'1234567890', 'holder':'Bob Barker','ccv_number':'123'})

However, how do you pass data to a custom field such as the one implemented here?

Answer 1

All fields have an ‘initial’ attribute so you set that even if it’s a custom field

https://code.djangoproject.com/browser/django/trunk/django/forms/fields.py#L45

so you should just be able to overwrite the constructor:

class PaymentForm(forms.Form):
    def __init__(self, exp = None, *args, **kwargs):
        super(PaymentForm, self).__init__(*args, **kwargs)
        if exp:
            self.fields['expiration'].initial = exp

and in your view you can pass the required data:

form = PaymentForm(exp=...)