Support legacy ruamel.yaml loaders

Upstream ruamel.yaml changes loaders in 0.17.0, with earlier loaders being
deprecated. However, the replacement loaders were introduced with the same
version. This update ensures that both loaders are being supported.

interfaces/cython/cantera/ck2yaml.py

@@ -1375,9 +1375,15 @@ def load_extra_file(self, path):
         """
         Load YAML-formatted entries from ``path`` on disk.
         """
-        yaml_ = yaml.YAML()
-        with open(path, 'rt', encoding="utf-8") as stream:
-            yml = yaml_.load(stream)
+        try:
+            yaml_ = yaml.YAML(typ="rt")
+            with open(path, 'rt', encoding="utf-8") as stream:
+                yml = yaml_.load(stream)
+        except yaml.constructor.ConstructorError:
+            with open(path, "rt", encoding="utf-8") as stream:
+                # Ensure that the loader remains backward-compatible with legacy
+                # ruamel.yaml versions (prior to 0.17.0).
+                yml = yaml.round_trip_load(stream)
 
         # do not overwrite reserved field names
         reserved = {'generator', 'input-files', 'cantera-version', 'date',

interfaces/cython/cantera/test/utilities.py

@@ -18,12 +18,17 @@
 CANTERA_DATA_PATH = Path(__file__).parents[1] / "data"
 
 
-def load_yaml(yml_file, typ="safe"):
-    # Load YAML data from file. The YAML loader defaults to "safe".
-    yaml_ = yaml.YAML(typ=typ)
-    with open(yml_file, "rt", encoding="utf-8") as stream:
-        return yaml_.load(stream)
-
+def load_yaml(yml_file):
+    # Load YAML data from file using the "safe" loading option.
+    try:
+        yaml_ = yaml.YAML(typ="safe")
+        with open(yml_file, "rt", encoding="utf-8") as stream:
+            return yaml_.load(stream)
+    except yaml.constructor.ConstructorError:
+        with open(yml_file, "rt", encoding="utf-8") as stream:
+            # Ensure that  the loader remains backward-compatible with legacy
+            # ruamel.yaml versions (prior to 0.17.0).
+            return yaml.safe_load(stream)
 
 class CanteraTest(unittest.TestCase):
     @classmethod