python类properties()的实例源码

def create_view(self, index, viewclass=None):
        """Creates and initializes the view for the data at `index`. The
        returned view is synced with the data, except for the pos/size
        properties.
        """
        if viewclass is None:
            viewclass = self.get_viewclass(index)
        if viewclass is None:
            return
        item = self[index]
        # FIXME: we could pass the data though the constructor, but that wont
        # work for kv-declared classes, and might lead the user to think it can
        # work for reloading as well.
        view = viewclass()
        if viewclass not in _view_base_cache:
            _view_base_cache[viewclass] = isinstance(view, RecycleViewMixin)

        if _view_base_cache[viewclass]:
            view.refresh_view_attrs(self.recycleview, item)
        else:
            for key, value in item.items():
                setattr(view, key, value)
        return view

def get_views(self, i_start, i_end):
        '''Gets a 2-tuple of the new and old views for the current viewport.
        The new views are synced to the data except for the size/pos
        properties.
        The old views need to be removed from the layout, and the new views
        added.
        '''
        current_views = self.views
        visible_views = {}
        new_views = []
        dirty_views = self.dirty_views
        get_view = self.get_view
        make_view_dirty = self.make_view_dirty

        # iterate though the visible view
        # add them into the container if not already done
        for index in range(i_start, i_end + 1):
            view = get_view(index)
            if not view:
                continue

            visible_views[index] = view
            current_views.pop(index, None)
            new_views.append((view, index))

        # put all the hidden view as dirty views
        for index, view in current_views.items():
            make_view_dirty(view, index)
        # save the current visible views
        self.views = visible_views
        return new_views, current_views.values()

def get_view(self, index):
        """Returns a view instance for the data at `index`. It looks through
        the various caches and finally creates a view if it doesn't exist.
        The returned view is synced with the data, except for the pos/size
        properties.
        """
        if index in self.views:
            return self.views[index]

        dirty_views = self.dirty_views
        viewclass = self.get_viewclass(index)
        if viewclass is None:
            return
        rv = self.recycleview
        stale = False
        view = None

        if viewclass in dirty_views:
            dirty_class = dirty_views[viewclass]
            if index in dirty_class:
                # we found ourself in the dirty list, no need to update data!
                view = dirty_class.pop(index)
            elif _cached_views[viewclass]:
                # global cache has this class, update data
                view, stale = _cached_views[viewclass].pop(), True
            elif dirty_class:
                # random any dirty view element - update data
                view, stale = dirty_class.popitem()[1], True
        elif _cached_views[viewclass]:
            # global cache has this class, update data
            view, stale = _cached_views[viewclass].pop(), True

        if view is None:
            # create a fresh one
            view = self.create_view(index, viewclass)

        if stale is True:
            item = self[index]
            if viewclass not in _view_base_cache:
                _view_base_cache[viewclass] = isinstance(view,
                                                         RecycleViewMixin)

            if _view_base_cache[viewclass]:
                view.refresh_view_attrs(rv, item)
            else:
                for key, value in item.items():
                    setattr(view, key, value)

        self.views[index] = view
        return view