Django form field for the Mexican CLABE (Clave Bancaria Estandarizada)

django_mexico_clabe_form_field.py

import re

from django import forms
from django.core.exceptions import ValidationError


class CLABEField(forms.Field):
    """
    Django form field for the mexican CLABE (Clave Bancaria Estandarizada,
    Spanish for "standardized banking cipher"), a banking standard for the
    numbering of bank accounts in Mexico.
    More info: https://en.wikipedia.org/wiki/CLABE
    """

    def to_python(self, value):
        if not value:
            return ''
        return value

    def validate(self, value):
        """
        Validate that the input is a valid CLABE number, that is, the last
        digit (the control digit or "digito de control") matches the formula
        specified to calculate it.
        """

        super(CLABEField, self).validate(value)

        # Remove whitespace characters
        orig_clabe = re.sub('\s+', '', value)

        # Validate that value is 18 digit
        if len(orig_clabe) != 18 or not orig_clabe.isdigit():
            raise ValidationError('Please introduce a valid CLABE number')

        # Get bank key, branch key and account number (first 17 digits)
        digitos_banco = orig_clabe[:-1]

        # Do the math
        factores_peso = "37137137137137137"
        productos = [(int(val[0]) * int(val[1])) % 10 for val in zip(digitos_banco, factores_peso)]
        sum_productos = sum(productos)
        mod_productos = sum_productos % 10
        digito_control = (10 - mod_productos) % 10

        # Confirm if our result digit is same as the one found in the last char
        if digito_control == int(orig_clabe[-1]):
            return True
        else:
            raise ValidationError('Please introduce a valid CLABE number')