Addresses #6:

- Specifying UTF-8 during JSON load allows the parser to handle line encodings.
- More detailed error handling to make JSON laoding issues clearing.

(done by @dvanselow)

Author: den-sq

python/ouroboros/cli.py

@@ -1,6 +1,6 @@
 from multiprocessing import freeze_support
-
 import argparse
+import sys
 
 from ouroboros.common.pipelines import backproject_pipeline, slice_pipeline
 from ouroboros.helpers.models import pretty_json_output
@@ -73,14 +73,20 @@ def main():
 
 
 def handle_slice(args):
+    print(f"Loading slice options from: {args.options}")
     slice_options = SliceOptions.load_from_json(args.options)
 
+    if slice_options is None:
+        print("Exiting due to errors loading slice options.", file=sys.stderr)
+        sys.exit(1)
+
+    print("Slice options loaded successfully.")
     pipeline, input_data = slice_pipeline(slice_options, True)
 
     _, error = pipeline.process(input_data)
 
     if error:
-        print(error)
+        print(f"Pipeline Error: {error}", file=sys.stderr)
 
     if args.verbose:
         print("\nCalculation Statistics:\n")
@@ -90,16 +96,30 @@ def handle_slice(args):
 
 
 def handle_backproject(args):
+    print(f"Loading backproject options from: {args.options}")
     backproject_options = BackprojectOptions.load_from_json(args.options)
 
+    if backproject_options is None:
+        print("Exiting due to errors loading backproject options.", file=sys.stderr)
+        sys.exit(1)
+
+    print("Backproject options loaded successfully."
+          f"Loading slice options from: {backproject_options.slice_options_path}")
+
     slice_options = SliceOptions.load_from_json(backproject_options.slice_options_path)
- 
+
+    if slice_options is None:
+        print("Exiting due to errors loading slice options specified within backproject options"
+              f"({backproject_options.slice_options_path}).", file=sys.stderr)
+        sys.exit(1)
+
+    print("Slice options loaded successfully.")
     pipeline, input_data = backproject_pipeline(backproject_options, slice_options, True)
 
     _, error = pipeline.process(input_data)
 
     if error:
-        print(error)
+        print(f"Pipeline Error: {error}", file=sys.stderr)
 
     if args.verbose:
         print("\nCalculation Statistics:\n")

python/ouroboros/helpers/models.py

@@ -1,5 +1,6 @@
 import json
 from pydantic import BaseModel, ValidationError
+import sys
 
 
 def pretty_json_output(obj: object) -> str:
@@ -37,28 +38,40 @@ def model_with_json(cls):
 
 
 def save_to_json(self: BaseModel, json_path: str):
-    with open(json_path, "w") as f:
-        f.write(self.to_json())
+    # Also specify encoding here for consistency
+    with open(json_path, "w", encoding='utf-8') as f:
+        # Add indent here for consistency? Or handle in Pydantic model
+        f.write(self.to_json(indent=4))
 
 
 @classmethod
-def load_from_json(cls: BaseModel, json_path: str):
+def load_from_json(cls: type[BaseModel], json_path: str) -> BaseModel | None:
+    """Loads a Pydantic model from a JSON file.
+
+    Args:
+        cls: The Pydantic model class.
+        json_path: Path to the JSON file.
+
+    Returns:
+        An instance of the model, or None if loading fails.
+    """
     try:
-        with open(json_path, "r") as f:
-            result = cls.from_json(f.read())
+        # Explicitly use utf-8 encoding
+        with open(json_path, "r", encoding='utf-8') as f:
+            # Use model_validate_json directly for better error context from Pydantic
+            result = cls.model_validate_json(f.read())
             return result
-    except ValidationError as e:
-        err = f"Error loading {cls.__name__} from JSON: {e}"
-        print(err)
-        return err
     except FileNotFoundError:
-        err = f"File not found at {json_path}"
-        print(err)
-        return err
-    except BaseException:
-        err = f"File at {json_path} is not a valid JSON file"
-        print(err)
-        return err
+        print(f"Error: File not found at {json_path}", file=sys.stderr)
+        return None
+    except (ValidationError, json.JSONDecodeError) as e:
+        # Catch specific Pydantic validation errors and JSON syntax errors
+        print(f"Error loading {cls.__name__} from JSON file '{json_path}':\n{e}", file=sys.stderr)
+        return None
+    except Exception as e:
+        # Catch other potential errors like permission denied, unicode issues etc.
+        print(f"Error reading or parsing file '{json_path}': {e}", file=sys.stderr)
+        return None
 
 
 def copy_values_from_other(self: BaseModel, other: BaseModel):