Fix evaluate() mutating input resource floats to Decimal

visit() in apply_parsed_path wrote get_data() results back into the
original dict in place, converting float values to Decimal. Replace
the in-place mutation with a new dict comprehension.

Closes #75

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ruscoder

fhirpathpy/__init__.py

@@ -84,8 +84,7 @@ def visit(node):
             return res
 
         if isinstance(data, dict) and not isinstance(data, FP_Type):
-            for key, value in data.items():
-                data[key] = visit(value)
+            return {key: visit(value) for key, value in data.items()}
 
         return data
 

tests/test_additional.py

@@ -23,6 +23,31 @@ def path_functions_test(resource, path):
     assert str(e.value) == "to_date called for a collection of length 2"
 
 
+def evaluate_does_not_mutate_float_values_test():
+    """evaluate() must not convert floats to Decimal in the caller's dict."""
+    qr = {
+        "resourceType": "QuestionnaireResponse",
+        "status": "completed",
+        "item": [
+            {
+                "linkId": "temperature",
+                "answer": [
+                    {
+                        "valueQuantity": {
+                            "value": 37.2,
+                            "unit": "°C",
+                            "system": "http://unitsofmeasure.org",
+                            "code": "Cel",
+                        }
+                    }
+                ],
+            }
+        ],
+    }
+    evaluate(qr, "QuestionnaireResponse.repeat(item).answer")
+    assert isinstance(qr["item"][0]["answer"][0]["valueQuantity"]["value"], float)
+
+
 def copy_deepcopy_test():
     copy_1 = copy.copy(evaluate({}, "@2018"))
     copy_2 = evaluate({}, "@2018").copy()