customizableplot.available_font_families: Fix for non-existent defaul…

…t family

Orange/widgets/visualize/utils/customizableplot.py

@@ -28,7 +28,12 @@ def available_font_families() -> List:
     if not QApplication.instance():
         _ = QApplication(sys.argv)
     fonts = QFontDatabase().families()
-    default = fonts.pop(fonts.index(default_font_family()))
+
+    default_family = default_font_family()
+    if default_family not in fonts:
+        return sorted(fonts, key=lambda s: s.replace(".", ""))
+
+    default = fonts.pop(fonts.index(default_family))
     defaults = [default]
 
     guessed_name = default.split()[0]

Orange/widgets/visualize/utils/tests/test_customizableplot.py

@@ -0,0 +1,28 @@
+import unittest
+from unittest.mock import patch, Mock
+
+from Orange.widgets.visualize.utils import customizableplot
+
+
+class TestFonts(unittest.TestCase):
+    def test_available_font_families(self):
+        with patch.object(customizableplot, "QFont") as font, \
+                patch.object(customizableplot, "QFontDatabase") as db:
+            font.return_value = Mock()
+            font.return_value.family = Mock(return_value = "mock family")
+
+            db.return_value = Mock()
+            db.return_value.families = Mock(
+                return_value=["a", ".d", "e", ".b", "mock family", "c"])
+            self.assertEqual(customizableplot.available_font_families(),
+                             ["mock family", "", "a", ".b", "c", ".d", "e"])
+
+            # It seems it's possible that default font family does not exist
+            # (see gh-5036)
+            db.return_value.families.return_value = ["a", ".d", "e", ".b", "c"]
+            self.assertEqual(customizableplot.available_font_families(),
+                             ["a", ".b", "c", ".d", "e"])
+
+
+if __name__ == "__main__":
+    unittest.main()