Used @cached_property for BaseForm.changed_data.

from django.utils.encoding import (

    force_text, python_2_unicode_compatible, smart_text,

)

from django.utils.functional import cached_property

from django.utils.html import conditional_escape, format_html, html_safe

from django.utils.safestring import mark_safe

from django.utils.translation import ugettext as _

        self.label_suffix = label_suffix if label_suffix is not None else _(':')

        self.empty_permitted = empty_permitted

        self._errors = None  # Stores the errors after clean() has been called.

        self._changed_data = None

        # The base_fields class attribute is the *class-wide* definition of

        # fields. Because a particular *instance* of the class might want to

        """

        return bool(self.changed_data)

    @property

    @cached_property

    def changed_data(self):

        if self._changed_data is None:

            self._changed_data = []

        data = []

        for name, field in self.fields.items():

            prefixed_name = self.add_prefix(name)

            data_value = field.widget.value_from_datadict(self.data, self.files, prefixed_name)

                        self.data, self.files, initial_prefixed_name))

                except ValidationError:

                    # Always assume data has changed if validation fails.

                        self._changed_data.append(name)

                    data.append(name)

                    continue

            if field.has_changed(initial_value, data_value):

                    self._changed_data.append(name)

        return self._changed_data

                data.append(name)

        return data

    @property

    def media(self):