Replace numpy-Python comparison with dtype (#210)

* fix: Replace numpy-Python comparison with dtype

* test: Add test

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    changed:
+    - Replaced unsafe numpy-Python comparison with use of numpy dtype to convert byte-string arrays to Unicode ones within enums

policyengine_core/enums/enum.py

@@ -49,8 +49,11 @@ def encode(cls, array: Union[EnumArray, np.ndarray]) -> EnumArray:
         if isinstance(array, EnumArray):
             return array
 
-        # if array.dtype.kind == "b":
-        if isinstance(array == 0, bool):
+        # First, convert byte-string arrays to Unicode-string arrays
+        # Confusingly, Numpy uses "S" to refer to byte-string arrays
+        # and "U" to refer to Unicode-string arrays, which are also
+        # referred to as the "str" type
+        if array.dtype.kind == "S":
             # Convert boolean array to string array
             array = array.astype(str)
 

tests/core/enums/test_enum.py

@@ -0,0 +1,39 @@
+import pytest
+import numpy as np
+from policyengine_core.enums.enum import Enum
+from policyengine_core.enums.enum_array import EnumArray
+
+
+def test_enum_creation():
+    """
+    Test to make sure that various types of numpy arrays
+    are correctly encoded to int-typed EnumArray instances;
+    check enum_array.py to see why int-typed
+    """
+
+    test_simple_array = ["MAXWELL", "DWORKIN", "MAXWELL"]
+
+    class Sample(Enum):
+        MAXWELL = "maxwell"
+        DWORKIN = "dworkin"
+
+    sample_string_array = np.array(test_simple_array)
+    sample_item_array = np.array(
+        [Sample.MAXWELL, Sample.DWORKIN, Sample.MAXWELL]
+    )
+    explicit_s_array = np.array(test_simple_array, "S")
+
+    encoded_array = Sample.encode(sample_string_array)
+    assert len(encoded_array) == 3
+    assert isinstance(encoded_array, EnumArray)
+    assert encoded_array.dtype.kind == "i"
+
+    encoded_array = Sample.encode(sample_item_array)
+    assert len(encoded_array) == 3
+    assert isinstance(encoded_array, EnumArray)
+    assert encoded_array.dtype.kind == "i"
+
+    encoded_array = Sample.encode(explicit_s_array)
+    assert len(encoded_array) == 3
+    assert isinstance(encoded_array, EnumArray)
+    assert encoded_array.dtype.kind == "i"