Fix deepcopy of primitive types

Author: ndrluis

pyiceberg/types.py

@@ -160,7 +160,7 @@ def is_struct(self) -> bool:
         return isinstance(self, StructType)
 
 
-class PrimitiveType(IcebergRootModel[str], IcebergType, Singleton):
+class PrimitiveType(Singleton, IcebergRootModel[str], IcebergType):
     """Base class for all Iceberg Primitive Types."""
 
     root: Any = Field()

pyiceberg/utils/singleton.py

@@ -47,3 +47,7 @@ def __new__(cls, *args, **kwargs):  # type: ignore
         if key not in cls._instances:
             cls._instances[key] = super().__new__(cls)
         return cls._instances[key]
+
+    def __deepcopy__(self, memo: Dict[int, Any]) -> Any:
+        """Return a deep copy of the Singleton class."""
+        return self

tests/test_types.py

@@ -619,3 +619,14 @@ def test_types_singleton() -> None:
     assert id(BooleanType()) == id(BooleanType())
     assert id(FixedType(22)) == id(FixedType(22))
     assert id(FixedType(19)) != id(FixedType(25))
+
+
+def test_deepcopy_of_singleton_fixed_type() -> None:
+    """FixedType is a singleton, so deepcopy should return the same instance"""
+    from copy import deepcopy
+
+    list_of_fixed_types = [FixedType(22), FixedType(19)]
+    copied_list = deepcopy(list_of_fixed_types)
+
+    for lhs, rhs in zip(list_of_fixed_types, copied_list):
+        assert id(lhs) == id(rhs)