Change isinstance checks to type(). Fixes #10

preserve.py

@@ -55,7 +55,7 @@ def preservable(cls, restore_method=RestoreMethod.DIRECT, name=None):
     if name is None:
         cls._preserve_name = cls.__name__
     else:
-        if isinstance(name, str):
+        if type(name) != str:
             raise Exception("Preservable name must be a string")
         cls._preserve_name = name
     cls._restore_method = restore_method
@@ -88,11 +88,12 @@ def preserve(target_obj):
     """
     # If it's a primitive, store it. If it's a dict or list, recursively preserve that.
     # If it's an instance of another preservable class, call its .preserve() method.
-    if isinstance(target_obj, (str, int, float, bool, type(None))):
+    obj_type = type(target_obj)
+    if obj_type in (str, int, float, bool, type(None)):
         return target_obj
-    elif isinstance(target_obj, dict):
+    elif obj_type == dict:
         return _preserve_dict(target_obj)
-    elif isinstance(target_obj, list):
+    elif obj_type == list:
         list_jam = []
         for val in target_obj:
             list_jam.append(preserve(val))
@@ -106,7 +107,7 @@ def preserve(target_obj):
 def _preserve_dict(target_dict):
     dict_jam = {}
     for k, val in target_dict.items():
-        if not isinstance(k, str):
+        if type(k) != str:
             raise Exception("Non-string dictionary keys are not preservable")
         if k == class_key:
             raise Exception("Key "+class_key+" is reserved for internal use")
@@ -124,11 +125,12 @@ def restore(obj_jam):
         obj_jam: The data structure to restore, usually the result of a
             ``preserve()`` call.
     """
-    if isinstance(obj_jam, (str, int, float, bool, type(None))):
+    obj_type = type(obj_jam)
+    if obj_type in (str, int, float, bool, type(None)):
         return obj_jam
-    elif isinstance(obj_jam, dict):
+    elif obj_type == dict:
         return _restore_dict(obj_jam)
-    elif isinstance(obj_jam, list):
+    elif obj_type == list:
         restored_list = []
         for val in obj_jam:
             restored_list.append(restore(val))
@@ -140,7 +142,7 @@ def restore(obj_jam):
 def _restore_dict(dict_jam):
     restored_dict = {}
     for k, val in dict_jam.items():
-        if not isinstance(k, str):
+        if type(k) != str:
             raise Exception("Non-string dictionary keys are not restorable")
         if k != class_key:
             restored_dict[k] = restore(val)

tests/test_preserve.py

@@ -45,6 +45,17 @@ def test_data_with_preservable(primitive_data):
     assert obj_attrs_and_type_equal(restored_data["preservable"], primitive_data["preservable"])
 
 
+
+def test_subclass_of_raw_preservable():
+    class RawPreservableSubclass(dict):
+        pass
+
+    # A subclass _shouldn't_ be preservable by default, as if it was restore() would
+    # return an instance of the parent class.
+    with pytest.raises(Exception, match="is not preservable"):
+        preserve.restore(preserve.preserve(RawPreservableSubclass()))
+
+
 def test_plain_class():
     # plain class is not preservable
     with pytest.raises(Exception, match="is not preservable"):