Merge pull request #159 from UCL/158-return-strs

Issue #158: Return empty string rather than None when there is no text

sksurgeryvtk/text/text_overlay.py

@@ -44,11 +44,17 @@ def get_text(self):
         Returns the current list of text annotations
         :return: [bottom-left, bottom-right, top-left, top-right]
         """
-        return [self.text_actor.GetText(0),
+
+        text = [self.text_actor.GetText(0),
                 self.text_actor.GetText(1),
                 self.text_actor.GetText(2),
                 self.text_actor.GetText(3)]
 
+        # Set None values to ''
+        text_all_str = ['' if x is None else x for x in text]
+
+        return text_all_str
+
     def set_text_on_top_left(self, text):
         """
         Set the text on the top-left corner.

tests/text/test_corner_annotaiton.py

@@ -44,10 +44,10 @@ def test_setter_getter(corner_annotaiton):
 
     initial = corner_annotaiton.get_text()
     assert len(initial) == 4
-    assert initial[0] is None
-    assert initial[1] is None
-    assert initial[2] is None
-    assert initial[3] is None
+    assert initial[0] is ''
+    assert initial[1] is ''
+    assert initial[2] is ''
+    assert initial[3] is ''
     stuff_to_set = ['Snappy', 'is', 'totally', 'awesome']
     corner_annotaiton.set_text(stuff_to_set)
     stuff_retrieved = corner_annotaiton.get_text()