tools.image: fixed compat issue with Py<3.10

Author: PierreRaybaut

plotpy/tools/image.py

@@ -47,8 +47,6 @@
 if TYPE_CHECKING:  # pragma: no cover
     from plotpy.plot import BasePlot
 
-MaskedItem = Union[MaskedImageItem, MaskedXYImageItem]
-
 
 class ImageStatsRectangle(AnnotatedRectangle):
     """ """
@@ -598,11 +596,12 @@ def find_masked_image(self, plot):
         :param plot:
         :return:
         """
+        maskedtypes = (MaskedImageItem, MaskedXYImageItem)
         item = plot.get_active_item()
-        if isinstance(item, MaskedItem):
+        if isinstance(item, maskedtypes):
             return item
         else:
-            items = [item for item in plot.get_items() if isinstance(item, MaskedItem)]
+            items = [item for item in plot.get_items() if isinstance(item, maskedtypes)]
             if items:
                 return items[-1]