Update to throw IndexError if model name not registered (#1475)

I wasn't really sure where else this change needed to be done. I added
this error message in this registry code since it will be called by the
same run_batch call that checks for prompts too

python/src/aiconfig/Config.py

@@ -365,7 +365,7 @@ async def run_batch(
 
         Raises:
             IndexError: If the identifier for the prompt doesn't exist in the list of available prompts.
-
+            IndexError: If the model name doesn't exist in the list of available model parsers.
         Returns:
             list[Tuple["ExecuteResult", JSONObject | Any, Dict[str, Any]]]: A list of tuples, each tuple consisting of the inference result, the corresponding resolved completion parameters, and the parameters dict used.
 

python/src/aiconfig/registry.py

@@ -61,6 +61,10 @@ def get_model_parser(model_id: str) -> ModelParser:
         Returns:
             ModelParser: The retrieved model parser
         """
+        if model_id not in ModelParserRegistry.parser_ids():
+            raise IndexError(
+                f"Model parser '{model_id}' not found in registry, available model parsers are:\n {ModelParserRegistry.parser_ids()}"
+            )
         return ModelParserRegistry._parsers[model_id]
 
     @staticmethod

python/tests/test_registry.py

@@ -88,7 +88,7 @@ def test_retrieve_model_parser(self):
 
     def test_retrieve_nonexistent_model_parser(self):
         # Attempt to retrieve a model parser that is not registered
-        with pytest.raises(KeyError):
+        with pytest.raises(IndexError):
             ModelParserRegistry.get_model_parser("nonexistent-model")
 
     def test_retrieve_model_parser_for_prompt(
@@ -134,7 +134,7 @@ def test_retrieve_model_parser_for_prompt_with_nonexistent_model(
         ai_config_runtime.add_prompt(prompt.name, prompt)
 
         # Attempt to retrieve a model parser for the Prompt
-        with pytest.raises(KeyError):
+        with pytest.raises(IndexError):
             ModelParserRegistry.get_model_parser_for_prompt(
                 prompt, ai_config_runtime
             ).id()
@@ -153,7 +153,7 @@ def test_remove_model_parser(self):
         ModelParserRegistry.remove_model_parser("model-8")
 
         # Attempt to retrieve the removed model parser
-        with pytest.raises(KeyError):
+        with pytest.raises(IndexError):
             parser = ModelParserRegistry.get_model_parser("model-8") == None
 
     def test_clear_registry(self):