Updated the python errorStatusHandler to escalate details from IndexError and NotImplementedError and made ImageSequenceReference provide a more helpful exception message when trying to get a frame url from a zero rate or zero duration instance. (#783)

Author: reinecke

src/opentimelineio/imageSequenceReference.cpp

@@ -69,7 +69,15 @@ ImageSequenceReference::ImageSequenceReference(std::string const& target_url_bas
 
     std::string
     ImageSequenceReference::target_url_for_image_number(int const image_number, ErrorStatus* error_status) const {
-        if (image_number >= this->number_of_images_in_sequence()) {
+        if (_rate == 0) {
+            *error_status = ErrorStatus(ErrorStatus::ILLEGAL_INDEX, "Zero rate sequence has no frames.");
+            return std::string();
+        }
+        else if (!this->available_range().has_value() || this->available_range().value().duration().value() == 0) {
+            *error_status = ErrorStatus(ErrorStatus::ILLEGAL_INDEX, "Zero duration sequences has no frames.");
+            return std::string();
+        }
+        else if (image_number >= this->number_of_images_in_sequence()) {
             *error_status = ErrorStatus(ErrorStatus::ILLEGAL_INDEX);
             return std::string();
         }

src/py-opentimelineio/opentimelineio-bindings/otio_errorStatusHandler.cpp

@@ -28,12 +28,12 @@ ErrorStatusHandler::~ErrorStatusHandler() noexcept(false) {
     if (!error_status) {
         return;
     }
-    
+
     switch(error_status.outcome) {
     case ErrorStatus::NOT_IMPLEMENTED:
-        throw py::not_implemented_error();
+        throw py::not_implemented_error(error_status.details);
     case ErrorStatus::ILLEGAL_INDEX:
-        throw py::index_error();
+        throw py::index_error(error_status.details);
     case ErrorStatus::KEY_NOT_FOUND:
         throw py::key_error(error_status.details);
     case ErrorStatus::INTERNAL_ERROR:

tests/test_image_sequence_reference.py

@@ -611,3 +611,53 @@ def test_negative_frame_numbers(self):
                 ref.target_url_for_image_number(i),
                 "file:///show/seq/shot/rndr/show_shot.{:04}.exr".format(i - 1),
             )
+
+    def test_target_url_for_image_number_with_missing_timing_info(self):
+        ref = otio.schema.ImageSequenceReference(
+            "file:///show/seq/shot/rndr/",
+            "show_shot.",
+            ".exr",
+            frame_zero_padding=4,
+            start_frame=1,
+            frame_step=1,
+            rate=24,
+        )
+
+        # Make sure the right error and a useful message raised when
+        # source_range is either un-set or zero duration.
+        with self.assertRaises(IndexError) as exception_manager:
+            ref.target_url_for_image_number(0)
+
+        self.assertEqual(
+            str(exception_manager.exception),
+            "Zero duration sequences has no frames.",
+        )
+
+        ref.available_range = otio.opentime.TimeRange(
+            otio.opentime.RationalTime(12, 24),
+            otio.opentime.RationalTime(0, 1),
+        )
+
+        with self.assertRaises(IndexError) as exception_manager:
+            ref.target_url_for_image_number(0)
+
+        self.assertEqual(
+            str(exception_manager.exception),
+            "Zero duration sequences has no frames.",
+        )
+
+        # Set the duration and make sure a similarly useful message comes
+        # when rate is un-set.
+        ref.available_range = otio.opentime.TimeRange(
+            otio.opentime.RationalTime(12, 24),
+            otio.opentime.RationalTime(48, 24),
+        )
+        ref.rate = 0
+
+        with self.assertRaises(IndexError) as exception_manager:
+            ref.target_url_for_image_number(0)
+
+        self.assertEqual(
+            str(exception_manager.exception),
+            "Zero rate sequence has no frames.",
+        )