from django import forms from django.db import models from django.utils.text import capfirst from django.core import exceptions class MultiSelectFormField(forms.MultipleChoiceField):     widget = forms.CheckboxSelectMultiple     def __init__(self, *args, **kwargs):         self.max_choices = kwargs.pop('max_choices', 0)         super(MultiSelectFormField, self).__init__(*args, **kwargs)     def clean(self, value):         if not value and self.required:             raise forms.ValidationError(self.error_messages['required'])         # if value and self.max_choices and len(value) > self.max_choices:         #     raise forms.ValidationError('You must select a maximum of %s choice%s.'         #             % (apnumber(self.max_choices), pluralize(self.max_choices)))         return value class MultiSelectField(models.Field):     __metaclass__ = models.SubfieldBase     def get_internal_type(self):         return "CharField"     def get_choices_default(self):         return self.get_choices(include_blank=False)     def _get_FIELD_display(self, field):         value = getattr(self, field.attname)         choicedict = dict(field.choices)     def formfield(self, **kwargs):         # don't call super, as that overrides default widget if it has choices         defaults = {'required': not self.blank, 'label': capfirst(self.verbose_name),                     'help_text': self.help_text, 'choices': self.choices}         if self.has_default():             defaults['initial'] = self.get_default()         defaults.update(kwargs)         return MultiSelectFormField(**defaults)     def get_prep_value(self, value):         return value     def get_db_prep_value(self, value, connection=None, prepared=False):         if isinstance(value, basestring):             return value         elif isinstance(value, list):             return ",".join(value)     def to_python(self, value):         if value is not None:             return value if isinstance(value, list) else value.split(',')         return ''     def contribute_to_class(self, cls, name):         super(MultiSelectField, self).contribute_to_class(cls, name)         if self.choices:             func = lambda self, fieldname = name, choicedict = dict(self.choices): ",".join([choicedict.get(value, value) for value in getattr(self, fieldname)])             setattr(cls, 'get_%s_display' % self.name, func)     def validate(self, value, model_instance):         arr_choices = self.get_choices_selected(self.get_choices_default())         for opt_select in value:             if (int(opt_select) not in arr_choices):  # the int() here is for comparing with integer choices                 raise exceptions.ValidationError(self.error_messages['invalid_choice'] % value)         return     def get_choices_selected(self, arr_choices=''):         if not arr_choices:             return False         list = []         for choice_selected in arr_choices:             list.append(choice_selected[0])         return list     def value_to_string(self, obj):         value = self._get_val_from_obj(obj)         return self.get_db_prep_value(value)