diff --git a/pydatastructs/linear_data_structures/arrays.py b/pydatastructs/linear_data_structures/arrays.py
index bf96ee5..cc92c93 100644
--- a/pydatastructs/linear_data_structures/arrays.py
+++ b/pydatastructs/linear_data_structures/arrays.py
@@ -63,9 +63,9 @@ class OneDimensionalArray(Array):
 
     .. [1] https://en.wikipedia.org/wiki/Array_data_structure#One-dimensional_arrays
     '''
-    
-    __slots__ = ['_size', '_data']
-    
+
+    __slots__ = ['_size', '_data', '_dtype']
+
     def __new__(cls, dtype=NoneType, *args, **kwargs):
         if dtype == NoneType or len(args) not in (1, 2):
             raise ValueError("1D array cannot be created due to incorrect"
diff --git a/pydatastructs/miscellaneous_data_structures/stack.py b/pydatastructs/miscellaneous_data_structures/stack.py
index e7f75a8..9b82ca4 100644
--- a/pydatastructs/miscellaneous_data_structures/stack.py
+++ b/pydatastructs/miscellaneous_data_structures/stack.py
@@ -84,8 +84,8 @@ class Stack(object):
 
 class ArrayStack(Stack):
 
-    __slots__ = ['maxsize', 'top', 'items']
-    
+    __slots__ = ['maxsize', 'top', 'items', 'dtype']
+
     def __new__(cls, maxsize=None, top=0, items=None, dtype=int):
         if not _check_type(maxsize, int):
             raise ValueError("maxsize is missing.")
diff --git a/pydatastructs/trees/binary_trees.py b/pydatastructs/trees/binary_trees.py
index a1d2aec..e8fb820 100644
--- a/pydatastructs/trees/binary_trees.py
+++ b/pydatastructs/trees/binary_trees.py
@@ -182,9 +182,7 @@ class BinarySearchTree(BinaryTree):
 
     pydatastructs.trees.binary_tree.BinaryTree
     """
-    
-    __slots__ = ['root_idx', 'comparator', 'tree', 'size']
-    
+
     def insert(self, key, data):
         walk = self.root_idx
         if self.tree[walk].key == None:
@@ -305,9 +303,6 @@ class AVLTree(BinarySearchTree):
     balance_factor = lambda self, node: self.right_height(node) - \
                                         self.left_height(node)
 
-    
-    __slots__ = ['root_idx', 'comparator', 'tree', 'size']
-    
     def _right_rotate(self, j, k):
         y = self.tree[k].right
         if y != None: