Added support for Norwegian bank account numbers

docs/authors.rst

@@ -80,6 +80,7 @@ Authors
 * Stefan Kjartansson
 * tadeo
 * Thiago Avelino
+* Thor K. Høgås
 * Tino de Bruijn
 * Trey Hunner
 * Tyler Ball

docs/changelog.rst

@@ -11,7 +11,8 @@ New flavors:
 
 New fields for existing flavors:
 
-- None
+- Added NOBankAccountNumber form field.
+  (`gh-275 <https://github.com/django/django-localflavor/pull/275>`_)
 
 Modifications to existing flavors:
 

localflavor/no/forms.py

@@ -7,11 +7,10 @@
 
 from django.core.validators import EMPTY_VALUES
 from django.forms import ValidationError
-from django.forms.fields import Field, RegexField, Select
+from django.forms.fields import CharField, Field, RegexField, Select
 from django.utils.translation import ugettext_lazy as _
 
 from localflavor.generic.forms import DeprecatedPhoneNumberFormFieldMixin
-
 from .no_municipalities import MUNICIPALITY_CHOICES
 
 
@@ -98,6 +97,70 @@ def _get_birthday(self, value):
         return birthday
 
 
+class NOBankAccountNumber(CharField):
+    """
+    A form field for Norwegian bank account numbers.
+
+    Performs MOD11 with the custom weights for the Norwegian bank account numbers,
+    including a check for a remainder of 0, in which event the checksum is also 0.
+
+    Usually their string representation is along the lines of ZZZZ.YY.XXXXX, where the last X is the check digit.
+    They're always a total of 11 digits long, with 10 out of these 11 being the actual account number itself.
+
+    * Accepts, and strips, account numbers with extra spaces.
+    * Accepts, and strips, account numbers provided in form of XXXX.YY.XXXXX.
+
+    .. note:: No consideration is taking for banking clearing numbers as of yet, seeing as these are only used between
+              banks themselves.
+
+    .. versionadded:: 1.5
+    """
+
+    default_error_messages = {
+        'invalid': _('Enter a valid Norwegian bank account number.'),
+        'invalid_checksum': _('Invalid control digit. Enter a valid Norwegian bank account number.'),
+        'invalid_length': _('Invalid length. Norwegian bank account numbers are 11 digits long.'),
+    }
+
+    def validate(self, value):
+        super(NOBankAccountNumber, self).validate(value)
+
+        if value is '':
+            # It's alright to be empty.
+            return
+        elif not value.isdigit():
+            # You must only contain decimals.
+            raise ValidationError(self.error_messages['invalid'])
+        elif len(value) is not 11:
+            # They only have one length: the number is 10!
+            # That being said, you always store them with the check digit included, so 11.
+            raise ValidationError(self.error_messages['invalid_length'])
+
+        # The control/check digit is the last digit
+        check_digit = int(value[-1])
+        bank_number = value[:-1]
+
+        # These are the weights by which we multiply to get our checksum digit
+        weights = [5, 4, 3, 2, 7, 6, 5, 4, 3, 2]
+        result = sum(w * (int(x)) for w, x in zip(weights, bank_number))
+        remainder = result % 11
+        # The checksum is 0 in the event there's no remainder, seeing as we cannot have a checksum of 11
+        # when 11 is one digit longer than we've got room for
+        checksum = 0 if remainder is 0 else 11 - remainder
+
+        if checksum != check_digit:
+            raise ValidationError(self.error_messages['invalid_checksum'])
+
+    def to_python(self, value):
+        value = super(NOBankAccountNumber, self).to_python(value)
+        return value.replace('.', '').replace(' ', '')
+
+    def prepare_value(self, value):
+        if value in EMPTY_VALUES:
+            return value
+        return '{}.{}.{}'.format(value[0:4], value[4:6], value[6:11])
+
+
 class NOPhoneNumberField(RegexField, DeprecatedPhoneNumberFormFieldMixin):
     """
     Field with phonenumber validation.

tests/test_no.py

@@ -3,7 +3,8 @@
 from django.utils.translation import ugettext_lazy as _
 from django.utils.translation import override
 
-from localflavor.no.forms import NOMunicipalitySelect, NOPhoneNumberField, NOSocialSecurityNumber, NOZipCodeField
+from localflavor.no.forms import (NOBankAccountNumber, NOMunicipalitySelect, NOPhoneNumberField, NOSocialSecurityNumber,
+                                  NOZipCodeField)
 
 
 class NOLocalFlavorTests(SimpleTestCase):
@@ -38,6 +39,39 @@ def test_NOPhoneNumberField(self):
         }
         self.assertFieldOutput(NOPhoneNumberField, valid, invalid)
 
+    def test_NOBankAccountNumber(self):
+        error_format = [_('Enter a valid Norwegian bank account number.')]
+        error_checksum = [_('Invalid control digit. Enter a valid Norwegian bank account number.')]
+        error_length = [_('Invalid length. Norwegian bank account numbers are 11 digits long.')]
+
+        # A good source of loads of highly-likely-to-be-valid examples are available at
+        # http://www.skatteetaten.no/no/Person/Skatteoppgjor/Restskatt/Kontonummer-til-skatteoppkreverkontorene/
+        valid = {
+            '7694 05 12057': '76940512057',
+            '7694.05.12057': '76940512057',
+            '7694.05.12057  ': '76940512057',
+            '1111.00.22222': '11110022222',
+            '5555.88.43216': '55558843216',
+            '63450618537': '63450618537',
+            ' 6345.06.20027 ': '63450620027',
+        }
+        invalid = {
+            '76940512056': error_checksum,  # invalid check digit
+            '1111.00.22228': error_checksum,  # invalid check digit
+            'abcdefgh': error_format,  # illegal characters, though it'll fail to create the checksum
+            '1111a00b22222': error_format,  # illegal characters
+            '769405120569': error_length,  # invalid length (and control number for that matter)
+        }
+        self.assertFieldOutput(NOBankAccountNumber, valid, invalid)
+
+    def test_NOBankAccountNumber_formatting(self):
+        form = NOBankAccountNumber()
+        self.assertEqual(form.prepare_value('76940512057'), '7694.05.12057')
+        # In the event there's already empty/blank/null values present.
+        # Any invalid data should be stopped by form.validate, which the above test should take care of.
+        self.assertEqual(form.prepare_value(None), None)
+        self.assertEqual(form.prepare_value(''), '')
+
     def test_NOSocialSecurityNumber(self):
         error_format = [_('Enter a valid Norwegian social security number.')]