class BaseModelFormSet

    def _existing_object(self, pk):
        if not hasattr(self, '_object_dict'):
            self._object_dict = {o.pk: o for o in self.get_queryset()}
        return self._object_dict.get(pk)

    def _get_to_python(self, field):
        """
        If the field is a related field, fetch the concrete field's (that
        is, the ultimate pointed-to field's) to_python.
        """
        while field.remote_field is not None:
            field = field.remote_field.get_related_field()
        return field.to_python

    def _should_delete_form(self, form):
        """Return whether or not the form was marked for deletion."""
        return form.cleaned_data.get(DELETION_FIELD_NAME, False)

    def add_prefix(self, index):
        return '%s-%s' % (self.prefix, index)

    def as_p(self):
        "Return this formset rendered as HTML <p>s."
        forms = ' '.join(form.as_p() for form in self)
        return mark_safe(str(self.management_form) + '\n' + forms)

    def as_table(self):
        "Return this formset rendered as HTML <tr>s -- excluding the <table></table>."
        # XXX: there is no semantic division between forms here, there
        # probably should be. It might make sense to render each form as a
        # table row with each field as a td.
        forms = ' '.join(form.as_table() for form in self)
        return mark_safe(str(self.management_form) + '\n' + forms)

    def as_ul(self):
        "Return this formset rendered as HTML <li>s."
        forms = ' '.join(form.as_ul() for form in self)
        return mark_safe(str(self.management_form) + '\n' + forms)

    def delete_existing(self, obj, commit=True):
        """Deletes an existing model instance."""
        if commit:
            obj.delete()

    def full_clean(self):
        """
        Clean all of self.data and populate self._errors and
        self._non_form_errors.
        """
        self._errors = []
        self._non_form_errors = self.error_class()
        empty_forms_count = 0

        if not self.is_bound:  # Stop further processing.
            return
        for i in range(0, self.total_form_count()):
            form = self.forms[i]
            # Empty forms are unchanged forms beyond those with initial data.
            if not form.has_changed() and i >= self.initial_form_count():
                empty_forms_count += 1
            # Accessing errors calls full_clean() if necessary.
            # _should_delete_form() requires cleaned_data.
            form_errors = form.errors
            if self.can_delete and self._should_delete_form(form):
                continue
            self._errors.append(form_errors)
        try:
            if (self.validate_max and
                    self.total_form_count() - len(self.deleted_forms) > self.max_num) or \
                    self.management_form.cleaned_data[TOTAL_FORM_COUNT] > self.absolute_max:
                raise ValidationError(ngettext(
                    "Please submit %d or fewer forms.",
                    "Please submit %d or fewer forms.", self.max_num) % self.max_num,
                    code='too_many_forms',
                )
            if (self.validate_min and
                    self.total_form_count() - len(self.deleted_forms) - empty_forms_count < self.min_num):
                raise ValidationError(ngettext(
                    "Please submit %d or more forms.",
                    "Please submit %d or more forms.", self.min_num) % self.min_num,
                    code='too_few_forms')
            # Give self.clean() a chance to do cross-form validation.
            self.clean()
        except ValidationError as e:
            self._non_form_errors = self.error_class(e.error_list)

    def get_date_error_message(self, date_check):
        return gettext(
            "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': str(date_check[1]),
        }

    def get_form_error(self):
        return gettext("Please correct the duplicate values below.")

    def get_form_kwargs(self, index):
        """
        Return additional keyword arguments for each individual formset form.

        index will be None if the form being constructed is a new empty
        form.
        """
        return self.form_kwargs.copy()

    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 get_unique_error_message(self, unique_check):
        if len(unique_check) == 1:
            return gettext("Please correct the duplicate data for %(field)s.") % {
                "field": unique_check[0],
            }
        else:
            return gettext("Please correct the duplicate data for %(field)s, which must be unique.") % {
                "field": get_text_list(unique_check, _("and")),
            }

    def has_changed(self):
        """Return True if data in any form differs from initial."""
        return any(form.has_changed() for form in self)

    def is_multipart(self):
        """
        Return True if the formset needs to be multipart, i.e. it
        has FileInput, or False otherwise.
        """
        if self.forms:
            return self.forms[0].is_multipart()
        else:
            return self.empty_form.is_multipart()

    def is_valid(self):
        """Return True if every form in self.forms is valid."""
        if not self.is_bound:
            return False
        # We loop over every form.errors here rather than short circuiting on the
        # first failure to make sure validation gets triggered for every form.
        forms_valid = True
        # This triggers a full clean.
        self.errors
        for i in range(0, self.total_form_count()):
            form = self.forms[i]
            if self.can_delete and self._should_delete_form(form):
                # This form is going to be deleted so any of its errors
                # shouldn't cause the entire formset to be invalid.
                continue
            forms_valid &= form.is_valid()
        return forms_valid and not self.non_form_errors()

    def non_form_errors(self):
        """
        Return an ErrorList of errors that aren't associated with a particular
        form -- i.e., from formset.clean(). Return an empty ErrorList if there
        are none.
        """
        if self._non_form_errors is None:
            self.full_clean()
        return self._non_form_errors

    def save(self, commit=True):
        """
        Save model instances for every form, adding and changing instances
        as necessary, and return 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)

    def save_existing(self, form, instance, commit=True):
        """Save and return an existing model instance for the given form."""
        return form.save(commit=commit)

    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:
            obj = form.instance
            # If the pk is None, it means either:
            # 1. The object is an unexpected empty model, created by invalid
            #    POST data such as an object outside the formset's queryset.
            # 2. The object was already deleted from the database.
            if obj.pk is None:
                continue
            if form in forms_to_delete:
                self.deleted_objects.append(obj)
                self.delete_existing(obj, commit=commit)
            elif 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(self, form, commit=True):
        """Save and return a new model instance for the given form."""
        return form.save(commit=commit)

    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 total_error_count(self):
        """Return the number of errors across all forms in the formset."""
        return len(self.non_form_errors()) +\
            sum(len(form_errors) for form_errors in self.errors)

    def total_form_count(self):
        """Return the total number of forms in this FormSet."""
        if self.is_bound:
            # return absolute_max if it is lower than the actual total form
            # count in the data; this is DoS protection to prevent clients
            # from forcing the server to instantiate arbitrary numbers of
            # forms
            return min(self.management_form.cleaned_data[TOTAL_FORM_COUNT], self.absolute_max)
        else:
            initial_forms = self.initial_form_count()
            total_forms = max(initial_forms, self.min_num) + self.extra
            # Allow all existing related objects/inlines to be displayed,
            # but don't allow extra beyond max_num.
            if initial_forms > self.max_num >= 0:
                total_forms = initial_forms
            elif total_forms > self.max_num >= 0:
                total_forms = self.max_num
        return total_forms

    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.update(unique_checks)
            all_date_checks.update(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 the data for the set of fields that must be unique among the forms.
                row_data = (
                    field if field in self.unique_fields else form.cleaned_data[field]
                    for field in unique_check if field in form.cleaned_data
                )
                # Reduce Model instances to their primary key values
                row_data = tuple(d._get_pk_val() if hasattr(d, '_get_pk_val') else d
                                 for d in row_data)
                if row_data and None not 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)