Pyupgrade to python3.8 (#3616)

* Upgrade to Python 3.8 syntax

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

data_structures/binary_tree/segment_tree_other.py

@@ -7,7 +7,7 @@ from collections.abc import Sequence
 from queue import Queue
 
 
-class SegmentTreeNode(object):
+class SegmentTreeNode:
     def __init__(self, start, end, val, left=None, right=None):
         self.start = start
         self.end = end
@@ -17,10 +17,10 @@ class SegmentTreeNode(object):
         self.right = right
 
     def __str__(self):
-        return "val: %s, start: %s, end: %s" % (self.val, self.start, self.end)
+        return f"val: {self.val}, start: {self.start}, end: {self.end}"
 
 
-class SegmentTree(object):
+class SegmentTree:
     """
     >>> import operator
     >>> num_arr = SegmentTree([2, 1, 5, 3, 4], operator.add)

data_structures/heap/heap.py

@@ -1,7 +1,7 @@
 #!/usr/bin/python3
 
 
-class Heap(object):
+class Heap:
     """
     >>> unsorted = [103, 9, 1, 7, 11, 15, 25, 201, 209, 107, 5]
     >>> h = Heap()

data_structures/linked_list/deque_doubly.py

@@ -20,7 +20,7 @@ class _DoublyLinkedBase:
             self._next = link_n
 
         def has_next_and_prev(self):
-            return " Prev -> {0}, Next -> {1}".format(
+            return " Prev -> {}, Next -> {}".format(
                 self._prev is not None, self._next is not None
             )