diff --git a/arcade/gui/property.py b/arcade/gui/property.py
index bc4a84bfc..e939a1bcd 100644
--- a/arcade/gui/property.py
+++ b/arcade/gui/property.py
@@ -10,7 +10,7 @@ class _Obs(Generic[P]):
     Internal holder for Property value and change listeners
     """
 
-    __slots__ = "value", "listeners"
+    __slots__ = ("value", "listeners")
 
     def __init__(self, value: P):
         self.value = value
@@ -26,7 +26,7 @@ class Property(Generic[P]):
     :param default_factory: A callable which returns the default value.
                             Will be called with the property and the instance
     """
-    __slots__ = "name", "default_factory", "obs"
+    __slots__ = ("name", "default_factory", "obs")
     name: str
 
     def __init__(self, default: Optional[P] = None, default_factory: Optional[Callable[[Any, Any], P]] = None):
@@ -112,7 +112,13 @@ class MyObject:
 
 
 class _ObservableDict(dict):
-    # Internal class to observe changes inside a native python dict.
+    """Internal class to observe changes inside a native python dict."""
+
+    __slots__ = (
+        "prop",
+        "obj"
+    )
+
     def __init__(self, prop: Property, instance, *largs):
         self.prop: Property = prop
         self.obj = ref(instance)
@@ -167,7 +173,13 @@ def set(self, instance, value: dict):
 
 
 class _ObservableList(list):
-    # Internal class to observe changes inside a native python list.
+    """Internal class to observe changes inside a native python list."""
+
+    __slots__ = (
+        "prop",
+        "obj"
+    )
+
     def __init__(self, prop: Property, instance, *largs):
         self.prop: Property = prop
         self.obj = ref(instance)
diff --git a/arcade/paths.py b/arcade/paths.py
index 6acd34987..f6b09fba1 100644
--- a/arcade/paths.py
+++ b/arcade/paths.py
@@ -74,7 +74,6 @@ class _AStarGraph(object):
     :param int bottom: Far bottom side y value
     :param int top: Far top side y value
     """
-
     def __init__(self, barriers: Union[List, Tuple, Set],
                  left: int,
                  right: int,