Fix NumPy Serialization

pyproject.toml

@@ -41,7 +41,7 @@ classifiers = [
 ]
 
 [project.optional-dependencies]
-test = ["pytest"]
+test = ["pytest", "numpy"]
 
 [project.urls]
 Documentation = "https://pals-project.readthedocs.io"

src/pals/functions.py

@@ -54,6 +54,25 @@ def load_file_to_dict(filename: str) -> dict:
     return pals_data
 
 
+def _numpy_to_native(obj):
+    """Convert a numpy scalar/array to its Python-native equivalent.
+
+    Returns ``None`` when the object is not a numpy type or when numpy is not
+    installed; callers use that to decide whether to fall back to the default
+    serializer behavior. numpy is an optional dependency.
+    """
+    try:
+        import numpy as np
+    except ImportError:
+        return None
+
+    if isinstance(obj, np.ndarray):
+        return obj.tolist()
+    if isinstance(obj, np.generic):
+        return obj.item()
+    return None
+
+
 def store_dict_to_file(filename: str, pals_dict: dict):
     file_noext, extension, file_noext_noext, extension_inner = inspect_file_extensions(
         filename
@@ -63,14 +82,58 @@ def store_dict_to_file(filename: str, pals_dict: dict):
     if extension == ".json":
         import json
 
-        json_data = json.dumps(pals_dict, sort_keys=False, indent=2)
+        def _json_default(obj):
+            native = _numpy_to_native(obj)
+            if native is not None:
+                return native
+            raise TypeError(
+                f"Object of type {type(obj).__name__} is not JSON serializable"
+            )
+
+        json_data = json.dumps(
+            pals_dict, sort_keys=False, indent=2, default=_json_default
+        )
         with open(filename, "w") as file:
             file.write(json_data)
 
     elif extension == ".yaml":
         import yaml
 
-        yaml_data = yaml.dump(pals_dict, default_flow_style=False, sort_keys=False)
+        # Subclass the safe dumper so numpy representers are scoped to PALS
+        # serialization and do not leak into the global pyyaml state used by
+        # other code in the same process.
+        class _PALSDumper(yaml.SafeDumper):
+            pass
+
+        try:
+            import numpy as np
+        except ImportError:
+            np = None
+
+        if np is not None:
+
+            def _represent_numpy_scalar(dumper, value):
+                native = value.item()
+                if isinstance(native, bool):
+                    return dumper.represent_bool(native)
+                if isinstance(native, int):
+                    return dumper.represent_int(native)
+                if isinstance(native, float):
+                    return dumper.represent_float(native)
+                return dumper.represent_data(native)
+
+            def _represent_numpy_array(dumper, value):
+                return dumper.represent_list(value.tolist())
+
+            _PALSDumper.add_multi_representer(np.generic, _represent_numpy_scalar)
+            _PALSDumper.add_representer(np.ndarray, _represent_numpy_array)
+
+        yaml_data = yaml.dump(
+            pals_dict,
+            Dumper=_PALSDumper,
+            default_flow_style=False,
+            sort_keys=False,
+        )
         with open(filename, "w") as file:
             file.write(yaml_data)
 

tests/test_serialization.py

@@ -1,5 +1,7 @@
 import os
 
+import pytest
+
 import pals
 
 
@@ -332,3 +334,75 @@ def test_comprehensive_lattice():
     # Clean up temporary files
     os.remove(yaml_file)
     os.remove(json_file)
+
+
+def _build_numpy_lattice(np):
+    """Build a small lattice using numpy-typed scalar values throughout."""
+    quad = pals.Quadrupole(
+        name="q_np",
+        length=np.float64(0.061),
+        MagneticMultipoleP=pals.MagneticMultipoleParameters(
+            Bn1=np.float64(-26.0), Bs1=np.float32(0.5), Kn0=np.int64(-1)
+        ),
+    )
+    oct_ = pals.Octupole(
+        name="o_np",
+        length=np.float64(0.25),
+        ElectricMultipoleP=pals.ElectricMultipoleParameters(
+            En3=np.float64(0.75), Es3=np.float32(0.125)
+        ),
+    )
+    return pals.BeamLine(name="line_np", line=[quad, oct_])
+
+
+def test_yaml_roundtrip_with_numpy():
+    """Regression test for issue #67: writing YAML with numpy-typed values
+    must not produce !!python/object tags, and round-tripping must yield
+    Python-native floats with the correct numeric values."""
+    np = pytest.importorskip("numpy")
+
+    line = _build_numpy_lattice(np)
+    yaml_file = "numpy_roundtrip.pals.yaml"
+    line.to_file(yaml_file)
+    try:
+        with open(yaml_file, "r") as f:
+            text = f.read()
+
+        # The bug symptom: YAML contains opaque numpy object tags.
+        assert "!!python/object" not in text, (
+            f"YAML output still contains unsafe numpy object tags:\n{text}"
+        )
+        assert "numpy" not in text, f"YAML output still references numpy:\n{text}"
+
+        loaded = pals.BeamLine.from_file(yaml_file)
+        loaded_quad = loaded.line[0]
+        assert loaded_quad.MagneticMultipoleP.Bn1 == -26.0
+        assert type(loaded_quad.MagneticMultipoleP.Bn1) is float
+        assert loaded_quad.MagneticMultipoleP.Bs1 == 0.5
+        assert loaded_quad.MagneticMultipoleP.Kn0 == -1
+
+        loaded_oct = loaded.line[1]
+        assert loaded_oct.ElectricMultipoleP.En3 == 0.75
+        assert type(loaded_oct.ElectricMultipoleP.En3) is float
+    finally:
+        if os.path.exists(yaml_file):
+            os.remove(yaml_file)
+
+
+def test_json_roundtrip_with_numpy():
+    """JSON path also needs to handle numpy values cleanly (defense-in-depth)."""
+    np = pytest.importorskip("numpy")
+
+    line = _build_numpy_lattice(np)
+    json_file = "numpy_roundtrip.pals.json"
+    line.to_file(json_file)
+    try:
+        loaded = pals.BeamLine.from_file(json_file)
+        loaded_quad = loaded.line[0]
+        assert loaded_quad.MagneticMultipoleP.Bn1 == -26.0
+        assert type(loaded_quad.MagneticMultipoleP.Bn1) is float
+        loaded_oct = loaded.line[1]
+        assert loaded_oct.ElectricMultipoleP.En3 == 0.75
+    finally:
+        if os.path.exists(json_file):
+            os.remove(json_file)