text: """
  Helper functions for creating Form classes from Django models
  and database field objects.
  """
  
  from __future__ import absolute_import, unicode_literals
  
  import warnings
  
  from django.core.exceptions import ValidationError, NON_FIELD_ERRORS, FieldError
  from django.forms.fields import Field, ChoiceField
  from django.forms.forms import BaseForm, get_declared_fields
  from django.forms.formsets import BaseFormSet, formset_factory
  from django.forms.util import ErrorList
  from django.forms.widgets import (SelectMultiple, HiddenInput,
      MultipleHiddenInput, media_property, CheckboxSelectMultiple)
  from django.utils.encoding import smart_text, force_text
  from django.utils.datastructures import SortedDict
  from django.utils import six
  from django.utils.text import get_text_list, capfirst
  from django.utils.translation import ugettext_lazy as _, ugettext, string_concat
  
  
  __all__ = (
      'ModelForm', 'BaseModelForm', 'model_to_dict', 'fields_for_model',
      'save_instance', 'ModelChoiceField', 'ModelMultipleChoiceField',
      'ALL_FIELDS',
  )
  
  ALL_FIELDS = '__all__'
  
  
  def construct_instance(form, instance, fields=None, exclude=None):
      """
      Constructs and returns a model instance from the bound ``form``'s
      ``cleaned_data``, but does not save the returned instance to the
      database.
      """
      from django.db import models
      opts = instance._meta
  
      cleaned_data = form.cleaned_data
      file_field_list = []
      for f in opts.fields:
          if not f.editable or isinstance(f, models.AutoField) \
                  or not f.name in cleaned_data:
              continue
          if fields is not None and f.name not in fields:
              continue
          if exclude and f.name in exclude:
              continue
          # Defer saving file-type fields until after the other fields, so a
          # callable upload_to can use the values from other fields.
          if isinstance(f, models.FileField):
              file_field_list.append(f)
          else:
              f.save_form_data(instance, cleaned_data[f.name])
  
      for f in file_field_list:
          f.save_form_data(instance, cleaned_data[f.name])
  
      return instance
  
  def save_instance(form, instance, fields=None, fail_message='saved',
                    commit=True, exclude=None, construct=True):
      """
      Saves bound Form ``form``'s cleaned_data into model instance ``instance``.
  
      If commit=True, then the changes to ``instance`` will be saved to the
      database. Returns ``instance``.
  
      If construct=False, assume ``instance`` has already been constructed and
      just needs to be saved.
      """
      if construct:
          instance = construct_instance(form, instance, fields, exclude)
      opts = instance._meta
      if form.errors:
          raise ValueError("The %s could not be %s because the data didn't"
                           " validate." % (opts.object_name, fail_message))
  
      # Wrap up the saving of m2m data as a function.
      def save_m2m():
          cleaned_data = form.cleaned_data
          for f in opts.many_to_many:
              if fields and f.name not in fields:
                  continue
              if f.name in cleaned_data:
                  f.save_form_data(instance, cleaned_data[f.name])
      if commit:
          # If we are committing, save the instance and the m2m data immediately.
          instance.save()
          save_m2m()
      else:
          # We're not committing. Add a method to the form to allow deferred
          # saving of m2m data.
          form.save_m2m = save_m2m
      return instance
  
  
  # ModelForms #################################################################
  
  def model_to_dict(instance, fields=None, exclude=None):
      """
      Returns a dict containing the data in ``instance`` suitable for passing as
      a Form's ``initial`` keyword argument.
  
      ``fields`` is an optional list of field names. If provided, only the named
      fields will be included in the returned dict.
  
      ``exclude`` is an optional list of field names. If provided, the named
      fields will be excluded from the returned dict, even if they are listed in
      the ``fields`` argument.
      """
      # avoid a circular import
      from django.db.models.fields.related import ManyToManyField
      opts = instance._meta
      data = {}
      for f in opts.concrete_fields + opts.many_to_many:
          if not f.editable:
              continue
          if fields and not f.name in fields:
              continue
          if exclude and f.name in exclude:
              continue
          if isinstance(f, ManyToManyField):
              # If the object doesn't have a primary key yet, just use an empty
              # list for its m2m fields. Calling f.value_from_object will raise
              # an exception.
              if instance.pk is None:
                  data[f.name] = []
              else:
                  # MultipleChoiceWidget needs a list of pks, not object instances.
                  data[f.name] = list(f.value_from_object(instance).values_list('pk', flat=True))
          else:
              data[f.name] = f.value_from_object(instance)
      return data
  
  def fields_for_model(model, fields=None, exclude=None, widgets=None, formfield_callback=None, localized_fields=None):
      """
      Returns a ``SortedDict`` containing form fields for the given model.
  
      ``fields`` is an optional list of field names. If provided, only the named
      fields will be included in the returned fields.
  
      ``exclude`` is an optional list of field names. If provided, the named
      fields will be excluded from the returned fields, even if they are listed
      in the ``fields`` argument.
  
      ``widgets`` is a dictionary of model field names mapped to a widget
  
      ``formfield_callback`` is a callable that takes a model field and returns
      a form field.
      """
      field_list = []
      ignored = []
      opts = model._meta
      for f in sorted(opts.concrete_fields + opts.many_to_many):
          if not f.editable:
              continue
          if fields is not None and not f.name in fields:
              continue
          if exclude and f.name in exclude:
              continue
  
          kwargs = {}
          if widgets and f.name in widgets:
              kwargs['widget'] = widgets[f.name]
          if localized_fields == ALL_FIELDS or (localized_fields and f.name in localized_fields):
              kwargs['localize'] = True
  
          if formfield_callback is None:
              formfield = f.formfield(**kwargs)
          elif not callable(formfield_callback):
              raise TypeError('formfield_callback must be a function or callable')
          else:
              formfield = formfield_callback(f, **kwargs)
  
          if formfield:
              field_list.append((f.name, formfield))
          else:
              ignored.append(f.name)
      field_dict = SortedDict(field_list)
      if fields:
          field_dict = SortedDict(
              [(f, field_dict.get(f)) for f in fields
                  if ((not exclude) or (exclude and f not in exclude)) and (f not in ignored)]
          )
      return field_dict
  
  class ModelFormOptions(object):
      def __init__(self, options=None):
          self.model = getattr(options, 'model', None)
          self.fields = getattr(options, 'fields', None)
          self.exclude = getattr(options, 'exclude', None)
          self.widgets = getattr(options, 'widgets', None)
          self.localized_fields = getattr(options, 'localized_fields', None)
  
  
  class ModelFormMetaclass(type):
      def __new__(cls, name, bases, attrs):
          formfield_callback = attrs.pop('formfield_callback', None)
          try:
              parents = [b for b in bases if issubclass(b, ModelForm)]
          except NameError:
              # We are defining ModelForm itself.
              parents = None
          declared_fields = get_declared_fields(bases, attrs, False)
          new_class = super(ModelFormMetaclass, cls).__new__(cls, name, bases,
                  attrs)
          if not parents:
              return new_class
  
          if 'media' not in attrs:
              new_class.media = media_property(new_class)
          opts = new_class._meta = ModelFormOptions(getattr(new_class, 'Meta', None))
  
          # We check if a string was passed to `fields` or `exclude`,
          # which is likely to be a mistake where the user typed ('foo') instead
          # of ('foo',)
          for opt in ['fields', 'exclude', 'localized_fields']:
              value = getattr(opts, opt)
              if isinstance(value, six.string_types) and value != ALL_FIELDS:
                  msg = ("%(model)s.Meta.%(opt)s cannot be a string. "
                         "Did you mean to type: ('%(value)s',)?" % {
                             'model': new_class.__name__,
                             'opt': opt,
                             'value': value,
                         })
                  raise TypeError(msg)
  
          if opts.model:
              # If a model is defined, extract form fields from it.
  
              if opts.fields is None and opts.exclude is None:
                  # This should be some kind of assertion error once deprecation
                  # cycle is complete.
                  warnings.warn("Creating a ModelForm without either the 'fields' attribute "
                                "or the 'exclude' attribute is deprecated - form %s "
                                "needs updating" % name,
                                PendingDeprecationWarning, stacklevel=2)
  
              if opts.fields == ALL_FIELDS:
                  # sentinel for fields_for_model to indicate "get the list of
                  # fields from the model"
                  opts.fields = None
  
              fields = fields_for_model(opts.model, opts.fields, opts.exclude,
                                        opts.widgets, formfield_callback, opts.localized_fields)
  
              # make sure opts.fields doesn't specify an invalid field
              none_model_fields = [k for k, v in six.iteritems(fields) if not v]
              missing_fields = set(none_model_fields) - \
                               set(declared_fields.keys())
              if missing_fields:
                  message = 'Unknown field(s) (%s) specified for %s'
                  message = message % (', '.join(missing_fields),
                                       opts.model.__name__)
                  raise FieldError(message)
              # Override default model fields with any custom declared ones
              # (plus, include all the other declared fields).
              fields.update(declared_fields)
          else:
              fields = declared_fields
          new_class.declared_fields = declared_fields
          new_class.base_fields = fields
          return new_class
  
  class BaseModelForm(BaseForm):
      def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                   initial=None, error_class=ErrorList, label_suffix=':',
                   empty_permitted=False, instance=None):
          opts = self._meta
          if opts.model is None:
              raise ValueError('ModelForm has no model class specified.')
          if instance is None:
              # if we didn't get an instance, instantiate a new one
              self.instance = opts.model()
              object_data = {}
          else:
              self.instance = instance
              object_data = model_to_dict(instance, opts.fields, opts.exclude)
          # if initial was provided, it should override the values from instance
          if initial is not None:
              object_data.update(initial)
          # self._validate_unique will be set to True by BaseModelForm.clean().
          # It is False by default so overriding self.clean() and failing to call
          # super will stop validate_unique from being called.
          self._validate_unique = False
          super(BaseModelForm, self).__init__(data, files, auto_id, prefix, object_data,
                                              error_class, label_suffix, empty_permitted)
  
      def _update_errors(self, message_dict):
          for k, v in message_dict.items():
              if k != NON_FIELD_ERRORS:
                  self._errors.setdefault(k, self.error_class()).extend(v)
                  # Remove the data from the cleaned_data dict since it was invalid
                  if k in self.cleaned_data:
                      del self.cleaned_data[k]
          if NON_FIELD_ERRORS in message_dict:
              messages = message_dict[NON_FIELD_ERRORS]
              self._errors.setdefault(NON_FIELD_ERRORS, self.error_class()).extend(messages)
  
      def _get_validation_exclusions(self):
          """
          For backwards-compatibility, several types of fields need to be
          excluded from model validation. See the following tickets for
          details: #12507, #12521, #12553
          """
          exclude = []
          # Build up a list of fields that should be excluded from model field
          # validation and unique checks.
          for f in self.instance._meta.fields:
              field = f.name
              # Exclude fields that aren't on the form. The developer may be
              # adding these values to the model after form validation.
              if field not in self.fields:
                  exclude.append(f.name)
  
              # Don't perform model validation on fields that were defined
              # manually on the form and excluded via the ModelForm's Meta
              # class. See #12901.
              elif self._meta.fields and field not in self._meta.fields:
                  exclude.append(f.name)
              elif self._meta.exclude and field in self._meta.exclude:
                  exclude.append(f.name)
  
              # Exclude fields that failed form validation. There's no need for
              # the model fields to validate them as well.
              elif field in self._errors.keys():
                  exclude.append(f.name)
  
              # Exclude empty fields that are not required by the form, if the
              # underlying model field is required. This keeps the model field
              # from raising a required error. Note: don't exclude the field from
              # validation if the model field allows blanks. If it does, the blank
              # value may be included in a unique check, so cannot be excluded
              # from validation.
              else:
                  form_field = self.fields[field]
                  field_value = self.cleaned_data.get(field, None)
                  if not f.blank and not form_field.required and field_value in form_field.empty_values:
                      exclude.append(f.name)
          return exclude
  
      def clean(self):
          self._validate_unique = True
          return self.cleaned_data
  
      def _post_clean(self):
          opts = self._meta
          # Update the model instance with self.cleaned_data.
          self.instance = construct_instance(self, self.instance, opts.fields, opts.exclude)
  
          exclude = self._get_validation_exclusions()
  
          # Foreign Keys being used to represent inline relationships
          # are excluded from basic field value validation. This is for two
          # reasons: firstly, the value may not be supplied (#12507; the
          # case of providing new values to the admin); secondly the
          # object being referred to may not yet fully exist (#12749).
          # However, these fields *must* be included in uniqueness checks,
          # so this can't be part of _get_validation_exclusions().
          for f_name, field in self.fields.items():
              if isinstance(field, InlineForeignKeyField):
                  exclude.append(f_name)
  
          # Clean the model instance's fields.
          try:
              self.instance.clean_fields(exclude=exclude)
          except ValidationError as e:
              self._update_errors(e.message_dict)
  
          # Call the model instance's clean method.
          try:
              self.instance.clean()
          except ValidationError as e:
              self._update_errors({NON_FIELD_ERRORS: e.messages})
  
          # Validate uniqueness if needed.
          if self._validate_unique:
              self.validate_unique()
  
      def validate_unique(self):
          """
          Calls the instance's validate_unique() method and updates the form's
          validation errors if any were raised.
          """
          exclude = self._get_validation_exclusions()
          try:
              self.instance.validate_unique(exclude=exclude)
          except ValidationError as e:
              self._update_errors(e.message_dict)
  
      def save(self, commit=True):
          """
          Saves this ``form``'s cleaned_data into model instance
          ``self.instance``.
  
          If commit=True, then the changes to ``instance`` will be saved to the
          database. Returns ``instance``.
          """
          if self.instance.pk is None:
              fail_message = 'created'
          else:
              fail_message = 'changed'
          return save_instance(self, self.instance, self._meta.fields,
                               fail_message, commit, construct=False)
  
      save.alters_data = True
  
  class ModelForm(six.with_metaclass(ModelFormMetaclass, BaseModelForm)):
      pass
  
  def modelform_factory(model, form=ModelForm, fields=None, exclude=None,
                        formfield_callback=None, widgets=None, localized_fields=None):
      """
      Returns a ModelForm containing form fields for the given model.
  
      ``fields`` is an optional list of field names. If provided, only the named
      fields will be included in the returned fields. If omitted or '__all__',
      all fields will be used.
  
      ``exclude`` is an optional list of field names. If provided, the named
      fields will be excluded from the returned fields, even if they are listed
      in the ``fields`` argument.
  
      ``widgets`` is a dictionary of model field names mapped to a widget.
  
      ``localized_fields`` is a list of names of fields which should be localized.
  
      ``formfield_callback`` is a callable that takes a model field and returns
      a form field.
      """
      # Create the inner Meta class. FIXME: ideally, we should be able to
      # construct a ModelForm without creating and passing in a temporary
      # inner class.
  
      # Build up a list of attributes that the Meta object will have.
      attrs = {'model': model}
      if fields is not None:
          attrs['fields'] = fields
      if exclude is not None:
          attrs['exclude'] = exclude
      if widgets is not None:
          attrs['widgets'] = widgets
      if localized_fields is not None:
          attrs['localized_fields'] = localized_fields
  
      # If parent form class already has an inner Meta, the Meta we're
      # creating needs to inherit from the parent's inner meta.
      parent = (object,)
      if hasattr(form, 'Meta'):
          parent = (form.Meta, object)
      Meta = type(str('Meta'), parent, attrs)
  
      # Give this new form class a reasonable name.
      class_name = model.__name__ + str('Form')
  
      # Class attributes for the new form class.
      form_class_attrs = {
          'Meta': Meta,
          'formfield_callback': formfield_callback
      }
  
      # The ModelFormMetaclass will trigger a similar warning/error, but this will
      # be difficult to debug for code that needs updating, so we produce the
      # warning here too.
      if (getattr(Meta, 'fields', None) is None and
          getattr(Meta, 'exclude', None) is None):
          warnings.warn("Calling modelform_factory without defining 'fields' or "
                        "'exclude' explicitly is deprecated",
                        PendingDeprecationWarning, stacklevel=2)
  
      # Instatiate type(form) in order to use the same metaclass as form.
      return type(form)(class_name, (form,), form_class_attrs)
  
  
  # ModelFormSets ##############################################################
  
  class BaseModelFormSet(BaseFormSet):
      """
      A ``FormSet`` for editing a queryset and/or adding new objects to it.
      """
      model = None
  
      def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                   queryset=None, **kwargs):
          self.queryset = queryset
          self.initial_extra = kwargs.pop('initial', None)
          defaults = {'data': data, 'files': files, 'auto_id': auto_id, 'prefix': prefix}
          defaults.update(kwargs)
          super(BaseModelFormSet, self).__init__(**defaults)
  
      def initial_form_count(self):
          """Returns the number of forms that are required in this FormSet."""
          if not (self.data or self.files):
              return len(self.get_queryset())
          return super(BaseModelFormSet, self).initial_form_count()
  
      def _existing_object(self, pk):
          if not hasattr(self, '_object_dict'):
              self._object_dict = dict([(o.pk, o) for o in self.get_queryset()])
          return self._object_dict.get(pk)
  
      def _construct_form(self, i, **kwargs):
          if self.is_bound and i < self.initial_form_count():
              # Import goes here instead of module-level because importing
              # django.db has side effects.
              from django.db import connections
              pk_key = "%s-%s" % (self.add_prefix(i), self.model._meta.pk.name)
              pk = self.data[pk_key]
              pk_field = self.model._meta.pk
              pk = pk_field.get_db_prep_lookup('exact', pk,
                  connection=connections[self.get_queryset().db])
              if isinstance(pk, list):
                  pk = pk[0]
              kwargs['instance'] = self._existing_object(pk)
          if i < self.initial_form_count() and not kwargs.get('instance'):
              kwargs['instance'] = self.get_queryset()[i]
          if i >= self.initial_form_count() and self.initial_extra:
              # Set initial values for extra forms
              try:
                  kwargs['initial'] = self.initial_extra[i-self.initial_form_count()]
              except IndexError:
                  pass
          return super(BaseModelFormSet, self)._construct_form(i, **kwargs)
  
      def get_queryset(self):
          if not hasattr(self, '_queryset'):
              if self.queryset is not None:
                  qs = self.queryset
              else:
                  qs = self.model._default_manager.get_queryset()
  
              # If the queryset isn't already ordered we need to add an
              # artificial ordering here to make sure that all formsets
              # constructed from this queryset have the same form order.
              if not qs.ordered:
                  qs = qs.order_by(self.model._meta.pk.name)
  
              # Removed queryset limiting here. As per discussion re: #13023
              # on django-dev, max_num should not prevent existing
              # related objects/inlines from being displayed.
              self._queryset = qs
          return self._queryset
  
      def save_new(self, form, commit=True):
          """Saves and returns a new model instance for the given form."""
          return form.save(commit=commit)
  
      def save_existing(self, form, instance, commit=True):
          """Saves and returns an existing model instance for the given form."""
          return form.save(commit=commit)
  
      def save(self, commit=True):
          """Saves model instances for every form, adding and changing instances
          as necessary, and returns the list of instances.
          """
          if not commit:
              self.saved_forms = []
              def save_m2m():
                  for form in self.saved_forms:
                      form.save_m2m()
              self.save_m2m = save_m2m
          return self.save_existing_objects(commit) + self.save_new_objects(commit)
  
      save.alters_data = True
  
      def clean(self):
          self.validate_unique()
  
      def validate_unique(self):
          # Collect unique_checks and date_checks to run from all the forms.
          all_unique_checks = set()
          all_date_checks = set()
          forms_to_delete = self.deleted_forms
          valid_forms = [form for form in self.forms if form.is_valid() and form not in forms_to_delete]
          for form in valid_forms:
              exclude = form._get_validation_exclusions()
              unique_checks, date_checks = form.instance._get_unique_checks(exclude=exclude)
              all_unique_checks = all_unique_checks.union(set(unique_checks))
              all_date_checks = all_date_checks.union(set(date_checks))
  
          errors = []
          # Do each of the unique checks (unique and unique_together)
          for uclass, unique_check in all_unique_checks:
              seen_data = set()
              for form in valid_forms:
                  # get data for each field of each of unique_check
                  row_data = tuple([form.cleaned_data[field] for field in unique_check if field in form.cleaned_data])
                  if row_data and not None in row_data:
                      # if we've already seen it then we have a uniqueness failure
                      if row_data in seen_data:
                          # poke error messages into the right places and mark
                          # the form as invalid
                          errors.append(self.get_unique_error_message(unique_check))
                          form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                          # remove the data from the cleaned_data dict since it was invalid
                          for field in unique_check:
                              if field in form.cleaned_data:
                                  del form.cleaned_data[field]
                      # mark the data as seen
                      seen_data.add(row_data)
          # iterate over each of the date checks now
          for date_check in all_date_checks:
              seen_data = set()
              uclass, lookup, field, unique_for = date_check
              for form in valid_forms:
                  # see if we have data for both fields
                  if (form.cleaned_data and form.cleaned_data[field] is not None
                      and form.cleaned_data[unique_for] is not None):
                      # if it's a date lookup we need to get the data for all the fields
                      if lookup == 'date':
                          date = form.cleaned_data[unique_for]
                          date_data = (date.year, date.month, date.day)
                      # otherwise it's just the attribute on the date/datetime
                      # object
                      else:
                          date_data = (getattr(form.cleaned_data[unique_for], lookup),)
                      data = (form.cleaned_data[field],) + date_data
                      # if we've already seen it then we have a uniqueness failure
                      if data in seen_data:
                          # poke error messages into the right places and mark
                          # the form as invalid
                          errors.append(self.get_date_error_message(date_check))
                          form._errors[NON_FIELD_ERRORS] = self.error_class([self.get_form_error()])
                          # remove the data from the cleaned_data dict since it was invalid
                          del form.cleaned_data[field]
                      # mark the data as seen
                      seen_data.add(data)
          if errors:
              raise ValidationError(errors)
  
      def get_unique_error_message(self, unique_check):
          if len(unique_check) == 1:
              return ugettext("Please correct the duplicate data for %(field)s.") % {
                  "field": unique_check[0],
              }
          else:
              return ugettext("Please correct the duplicate data for %(field)s, "
                  "which must be unique.") % {
                      "field": get_text_list(unique_check, six.text_type(_("and"))),
                  }
  
      def get_date_error_message(self, date_check):
          return ugettext("Please correct the duplicate data for %(field_name)s "
              "which must be unique for the %(lookup)s in %(date_field)s.") % {
              'field_name': date_check[2],
              'date_field': date_check[3],
              'lookup': six.text_type(date_check[1]),
          }
  
      def get_form_error(self):
          return ugettext("Please correct the duplicate values below.")
  
      def save_existing_objects(self, commit=True):
          self.changed_objects = []
          self.deleted_objects = []
          if not self.initial_forms:
              return []
  
          saved_instances = []
          forms_to_delete = self.deleted_forms
          for form in self.initial_forms:
              pk_name = self._pk_field.name
              raw_pk_value = form._raw_value(pk_name)
  
              # clean() for different types of PK fields can sometimes return
              # the model instance, and sometimes the PK. Handle either.
              pk_value = form.fields[pk_name].clean(raw_pk_value)
              pk_value = getattr(pk_value, 'pk', pk_value)
  
              obj = self._existing_object(pk_value)
              if form in forms_to_delete:
                  self.deleted_objects.append(obj)
                  obj.delete()
                  continue
              if form.has_changed():
                  self.changed_objects.append((obj, form.changed_data))
                  saved_instances.append(self.save_existing(form, obj, commit=commit))
                  if not commit:
                      self.saved_forms.append(form)
          return saved_instances
  
      def save_new_objects(self, commit=True):
          self.new_objects = []
          for form in self.extra_forms:
              if not form.has_changed():
                  continue
              # If someone has marked an add form for deletion, don't save the
              # object.
              if self.can_delete and self._should_delete_form(form):
                  continue
              self.new_objects.append(self.save_new(form, commit=commit))
              if not commit:
                  self.saved_forms.append(form)
          return self.new_objects
  
      def add_fields(self, form, index):
          """Add a hidden field for the object's primary key."""
          from django.db.models import AutoField, OneToOneField, ForeignKey
          self._pk_field = pk = self.model._meta.pk
          # If a pk isn't editable, then it won't be on the form, so we need to
          # add it here so we can tell which object is which when we get the
          # data back. Generally, pk.editable should be false, but for some
          # reason, auto_created pk fields and AutoField's editable attribute is
          # True, so check for that as well.
          def pk_is_not_editable(pk):
              return ((not pk.editable) or (pk.auto_created or isinstance(pk, AutoField))
                  or (pk.rel and pk.rel.parent_link and pk_is_not_editable(pk.rel.to._meta.pk)))
          if pk_is_not_editable(pk) or pk.name not in form.fields:
              if form.is_bound:
                  pk_value = form.instance.pk
              else:
                  try:
                      if index is not None:
                          pk_value = self.get_queryset()[index].pk
                      else:
                          pk_value = None
                  except IndexError:
                      pk_value = None
              if isinstance(pk, OneToOneField) or isinstance(pk, ForeignKey):
                  qs = pk.rel.to._default_manager.get_queryset()
              else:
                  qs = self.model._default_manager.get_queryset()
              qs = qs.using(form.instance._state.db)
              if form._meta.widgets:
                  widget = form._meta.widgets.get(self._pk_field.name, HiddenInput)
              else:
                  widget = HiddenInput
              form.fields[self._pk_field.name] = ModelChoiceField(qs, initial=pk_value, required=False, widget=widget)
          super(BaseModelFormSet, self).add_fields(form, index)
  
  def modelformset_factory(model, form=ModelForm, formfield_callback=None,
                           formset=BaseModelFormSet, extra=1, can_delete=False,
                           can_order=False, max_num=None, fields=None, exclude=None,
                           widgets=None, validate_max=False, localized_fields=None):
      """
      Returns a FormSet class for the given Django model class.
      """
      # modelform_factory will produce the same warning/error, but that will be
      # difficult to debug for code that needs upgrading, so we produce the
      # warning here too. This logic is reproducing logic inside
      # modelform_factory, but it can be removed once the deprecation cycle is
      # complete, since the validation exception will produce a helpful
      # stacktrace.
      meta = getattr(form, 'Meta', None)
      if meta is None:
          meta = type(str('Meta'), (object,), {})
      if (getattr(meta, 'fields', fields) is None and
          getattr(meta, 'exclude', exclude) is None):
          warnings.warn("Calling modelformset_factory without defining 'fields' or "
                        "'exclude' explicitly is deprecated",
                        PendingDeprecationWarning, stacklevel=2)
  
      form = modelform_factory(model, form=form, fields=fields, exclude=exclude,
                               formfield_callback=formfield_callback,
                               widgets=widgets, localized_fields=localized_fields)
      FormSet = formset_factory(form, formset, extra=extra, max_num=max_num,
                                can_order=can_order, can_delete=can_delete,
                                validate_max=validate_max)
      FormSet.model = model
      return FormSet
  
  
  # InlineFormSets #############################################################
  
  class BaseInlineFormSet(BaseModelFormSet):
      """A formset for child objects related to a parent."""
      def __init__(self, data=None, files=None, instance=None,
                   save_as_new=False, prefix=None, queryset=None, **kwargs):
          if instance is None:
              self.instance = self.fk.rel.to()
          else:
              self.instance = instance
          self.save_as_new = save_as_new
          if queryset is None:
              queryset = self.model._default_manager
          if self.instance.pk:
              qs = queryset.filter(**{self.fk.name: self.instance})
          else:
              qs = queryset.none()
          super(BaseInlineFormSet, self).__init__(data, files, prefix=prefix,
                                                  queryset=qs, **kwargs)
  
      def initial_form_count(self):
          if self.save_as_new:
              return 0
          return super(BaseInlineFormSet, self).initial_form_count()
  
  
      def _construct_form(self, i, **kwargs):
          form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs)
          if self.save_as_new:
              # Remove the primary key from the form's data, we are only
              # creating new instances
              form.data[form.add_prefix(self._pk_field.name)] = None
  
              # Remove the foreign key from the form's data
              form.data[form.add_prefix(self.fk.name)] = None
  
          # Set the fk value here so that the form can do its validation.
          setattr(form.instance, self.fk.get_attname(), self.instance.pk)
          return form
  
      @classmethod
      def get_default_prefix(cls):
          from django.db.models.fields.related import RelatedObject
          return RelatedObject(cls.fk.rel.to, cls.model, cls.fk).get_accessor_name().replace('+','')
  
      def save_new(self, form, commit=True):
          # Use commit=False so we can assign the parent key afterwards, then
          # save the object.
          obj = form.save(commit=False)
          pk_value = getattr(self.instance, self.fk.rel.field_name)
          setattr(obj, self.fk.get_attname(), getattr(pk_value, 'pk', pk_value))
          if commit:
              obj.save()
          # form.save_m2m() can be called via the formset later on if commit=False
          if commit and hasattr(form, 'save_m2m'):
              form.save_m2m()
          return obj
  
      def add_fields(self, form, index):
          super(BaseInlineFormSet, self).add_fields(form, index)
          if self._pk_field == self.fk:
              name = self._pk_field.name
              kwargs = {'pk_field': True}
          else:
              # The foreign key field might not be on the form, so we poke at the
              # Model field to get the label, since we need that for error messages.
              name = self.fk.name
              kwargs = {
                  'label': getattr(form.fields.get(name), 'label', capfirst(self.fk.verbose_name))
              }
              if self.fk.rel.field_name != self.fk.rel.to._meta.pk.name:
                  kwargs['to_field'] = self.fk.rel.field_name
  
          form.fields[name] = InlineForeignKeyField(self.instance, **kwargs)
  
          # Add the generated field to form._meta.fields if it's defined to make
          # sure validation isn't skipped on that field.
          if form._meta.fields:
              if isinstance(form._meta.fields, tuple):
                  form._meta.fields = list(form._meta.fields)
              form._meta.fields.append(self.fk.name)
  
      def get_unique_error_message(self, unique_check):
          unique_check = [field for field in unique_check if field != self.fk.name]
          return super(BaseInlineFormSet, self).get_unique_error_message(unique_check)
  
  
  def _get_foreign_key(parent_model, model, fk_name=None, can_fail=False):
      """
      Finds and returns the ForeignKey from model to parent if there is one
      (returns None if can_fail is True and no such field exists). If fk_name is
      provided, assume it is the name of the ForeignKey field. Unles can_fail is
      True, an exception is raised if there is no ForeignKey from model to
      parent_model.
      """
      # avoid circular import
      from django.db.models import ForeignKey
      opts = model._meta
      if fk_name:
          fks_to_parent = [f for f in opts.fields if f.name == fk_name]
          if len(fks_to_parent) == 1:
              fk = fks_to_parent[0]
              if not isinstance(fk, ForeignKey) or \
                      (fk.rel.to != parent_model and
                       fk.rel.to not in parent_model._meta.get_parent_list()):
                  raise Exception("fk_name '%s' is not a ForeignKey to %s" % (fk_name, parent_model))
          elif len(fks_to_parent) == 0:
              raise Exception("%s has no field named '%s'" % (model, fk_name))
      else:
          # Try to discover what the ForeignKey from model to parent_model is
          fks_to_parent = [
              f for f in opts.fields
              if isinstance(f, ForeignKey)
              and (f.rel.to == parent_model
                  or f.rel.to in parent_model._meta.get_parent_list())
          ]
          if len(fks_to_parent) == 1:
              fk = fks_to_parent[0]
          elif len(fks_to_parent) == 0:
              if can_fail:
                  return
              raise Exception("%s has no ForeignKey to %s" % (model, parent_model))
          else:
              raise Exception("%s has more than 1 ForeignKey to %s" % (model, parent_model))
      return fk
  
  
  def inlineformset_factory(parent_model, model, form=ModelForm,
                            formset=BaseInlineFormSet, fk_name=None,
                            fields=None, exclude=None, extra=3, can_order=False,
                            can_delete=True, max_num=None, formfield_callback=None,
                            widgets=None, validate_max=False, localized_fields=None):
      """
      Returns an ``InlineFormSet`` for the given kwargs.
  
      You must provide ``fk_name`` if ``model`` has more than one ``ForeignKey``
      to ``parent_model``.
      """
      fk = _get_foreign_key(parent_model, model, fk_name=fk_name)
      # enforce a max_num=1 when the foreign key to the parent model is unique.
      if fk.unique:
          max_num = 1
      kwargs = {
          'form': form,
          'formfield_callback': formfield_callback,
          'formset': formset,
          'extra': extra,
          'can_delete': can_delete,
          'can_order': can_order,
          'fields': fields,
          'exclude': exclude,
          'max_num': max_num,
          'widgets': widgets,
          'validate_max': validate_max,
          'localized_fields': localized_fields,
      }
      FormSet = modelformset_factory(model, **kwargs)
      FormSet.fk = fk
      return FormSet
  
  
  # Fields #####################################################################
  
  class InlineForeignKeyField(Field):
      """
      A basic integer field that deals with validating the given value to a
      given parent instance in an inline.
      """
      widget = HiddenInput
      default_error_messages = {
          'invalid_choice': _('The inline foreign key did not match the parent instance primary key.'),
      }
  
      def __init__(self, parent_instance, *args, **kwargs):
          self.parent_instance = parent_instance
          self.pk_field = kwargs.pop("pk_field", False)
          self.to_field = kwargs.pop("to_field", None)
          if self.parent_instance is not None:
              if self.to_field:
                  kwargs["initial"] = getattr(self.parent_instance, self.to_field)
              else:
                  kwargs["initial"] = self.parent_instance.pk
          kwargs["required"] = False
          super(InlineForeignKeyField, self).__init__(*args, **kwargs)
  
      def clean(self, value):
          if value in self.empty_values:
              if self.pk_field:
                  return None
              # if there is no value act as we did before.
              return self.parent_instance
          # ensure the we compare the values as equal types.
          if self.to_field:
              orig = getattr(self.parent_instance, self.to_field)
          else:
              orig = self.parent_instance.pk
          if force_text(value) != force_text(orig):
              raise ValidationError(self.error_messages['invalid_choice'])
          return self.parent_instance
  
      def _has_changed(self, initial, data):
          return False
  
  class ModelChoiceIterator(object):
      def __init__(self, field):
          self.field = field
          self.queryset = field.queryset
  
      def __iter__(self):
          if self.field.empty_label is not None:
              yield ("", self.field.empty_label)
          if self.field.cache_choices:
              if self.field.choice_cache is None:
                  self.field.choice_cache = [
                      self.choice(obj) for obj in self.queryset.all()
                  ]
              for choice in self.field.choice_cache:
                  yield choice
          else:
              for obj in self.queryset.all():
                  yield self.choice(obj)
  
      def __len__(self):
          return len(self.queryset) +\
                      (1 if self.field.empty_label is not None else 0)
  
      def choice(self, obj):
          return (self.field.prepare_value(obj), self.field.label_from_instance(obj))
  
  class ModelChoiceField(ChoiceField):
      """A ChoiceField whose choices are a model QuerySet."""
      # This class is a subclass of ChoiceField for purity, but it doesn't
      # actually use any of ChoiceField's implementation.
      default_error_messages = {
          'invalid_choice': _('Select a valid choice. That choice is not one of'
                              ' the available choices.'),
      }
  
      def __init__(self, queryset, empty_label="---------", cache_choices=False,
                   required=True, widget=None, label=None, initial=None,
                   help_text='', to_field_name=None, *args, **kwargs):
          if required and (initial is not None):
              self.empty_label = None
          else:
              self.empty_label = empty_label
          self.cache_choices = cache_choices
  
          # Call Field instead of ChoiceField __init__() because we don't need
          # ChoiceField.__init__().
          Field.__init__(self, required, widget, label, initial, help_text,
                         *args, **kwargs)
          self.queryset = queryset
          self.choice_cache = None
          self.to_field_name = to_field_name
  
      def __deepcopy__(self, memo):
          result = super(ChoiceField, self).__deepcopy__(memo)
          # Need to force a new ModelChoiceIterator to be created, bug #11183
          result.queryset = result.queryset
          return result
  
      def _get_queryset(self):
          return self._queryset
  
      def _set_queryset(self, queryset):
          self._queryset = queryset
          self.widget.choices = self.choices
  
      queryset = property(_get_queryset, _set_queryset)
  
      # this method will be used to create object labels by the QuerySetIterator.
      # Override it to customize the label.
      def label_from_instance(self, obj):
          """
          This method is used to convert objects into strings; it's used to
          generate the labels for the choices presented by this object. Subclasses
          can override this method to customize the display of the choices.
          """
          return smart_text(obj)
  
      def _get_choices(self):
          # If self._choices is set, then somebody must have manually set
          # the property self.choices. In this case, just return self._choices.
          if hasattr(self, '_choices'):
              return self._choices
  
          # Otherwise, execute the QuerySet in self.queryset to determine the
          # choices dynamically. Return a fresh ModelChoiceIterator that has not been
          # consumed. Note that we're instantiating a new ModelChoiceIterator *each*
          # time _get_choices() is called (and, thus, each time self.choices is
          # accessed) so that we can ensure the QuerySet has not been consumed. This
          # construct might look complicated but it allows for lazy evaluation of
          # the queryset.
          return ModelChoiceIterator(self)
  
      choices = property(_get_choices, ChoiceField._set_choices)
  
      def prepare_value(self, value):
          if hasattr(value, '_meta'):
              if self.to_field_name:
                  return value.serializable_value(self.to_field_name)
              else:
                  return value.pk
          return super(ModelChoiceField, self).prepare_value(value)
  
      def to_python(self, value):
          if value in self.empty_values:
              return None
          try:
              key = self.to_field_name or 'pk'
              value = self.queryset.get(**{key: value})
          except (ValueError, self.queryset.model.DoesNotExist):
              raise ValidationError(self.error_messages['invalid_choice'])
          return value
  
      def validate(self, value):
          return Field.validate(self, value)
  
      def _has_changed(self, initial, data):
          initial_value = initial if initial is not None else ''
          data_value = data if data is not None else ''
          return force_text(self.prepare_value(initial_value)) != force_text(data_value)
  
  class ModelMultipleChoiceField(ModelChoiceField):
      """A MultipleChoiceField whose choices are a model QuerySet."""
      widget = SelectMultiple
      hidden_widget = MultipleHiddenInput
      default_error_messages = {
          'list': _('Enter a list of values.'),
          'invalid_choice': _('Select a valid choice. %(value)s is not one of the'
                              ' available choices.'),
          'invalid_pk_value': _('"%(pk)s" is not a valid value for a primary key.')
      }
  
      def __init__(self, queryset, cache_choices=False, required=True,
                   widget=None, label=None, initial=None,
                   help_text='', *args, **kwargs):
          super(ModelMultipleChoiceField, self).__init__(queryset, None,
              cache_choices, required, widget, label, initial, help_text,
              *args, **kwargs)
          # Remove this in Django 1.8
          if isinstance(self.widget, SelectMultiple) and not isinstance(self.widget, CheckboxSelectMultiple):
              msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
              self.help_text = string_concat(self.help_text, ' ', msg)
  
      def clean(self, value):
          if self.required and not value:
              raise ValidationError(self.error_messages['required'])
          elif not self.required and not value:
              return self.queryset.none()
          if not isinstance(value, (list, tuple)):
              raise ValidationError(self.error_messages['list'])
          key = self.to_field_name or 'pk'
          for pk in value:
              try:
                  self.queryset.filter(**{key: pk})
              except ValueError:
                  raise ValidationError(self.error_messages['invalid_pk_value'] % {'pk': pk})
          qs = self.queryset.filter(**{'%s__in' % key: value})
          pks = set([force_text(getattr(o, key)) for o in qs])
          for val in value:
              if force_text(val) not in pks:
                  raise ValidationError(self.error_messages['invalid_choice'] % {'value': val})
          # Since this overrides the inherited ModelChoiceField.clean
          # we run custom validators here
          self.run_validators(value)
          return qs
  
      def prepare_value(self, value):
          if (hasattr(value, '__iter__') and
                  not isinstance(value, six.text_type) and
                  not hasattr(value, '_meta')):
              return [super(ModelMultipleChoiceField, self).prepare_value(v) for v in value]
          return super(ModelMultipleChoiceField, self).prepare_value(value)
  
      def _has_changed(self, initial, data):
          if initial is None:
              initial = []
          if data is None:
              data = []
          if len(initial) != len(data):
              return True
          initial_set = set([force_text(value) for value in self.prepare_value(initial)])
          data_set = set([force_text(value) for value in data])
          return data_set != initial_set
  
  
  def modelform_defines_fields(form_class):
      return (form_class is not None and (
              hasattr(form_class, '_meta') and
              (form_class._meta.fields is not None or
               form_class._meta.exclude is not None)
              ))
  