diff --git a/dynamic_programming/longest_arithmetic_subsequence.py b/dynamic_programming/longest_arithmetic_subsequence.py
index 74cb11b0b..781af9ef6 100644
--- a/dynamic_programming/longest_arithmetic_subsequence.py
+++ b/dynamic_programming/longest_arithmetic_subsequence.py
@@ -9,6 +9,7 @@ Note that:
   seq.length - 1).
 """
 
+
 def longest_arithmetic_subsequence(nums: list[int]) -> int:
     """
     Finds the length of the longest arithmetic subsequence in a given array of integers.
@@ -40,7 +41,7 @@ def longest_arithmetic_subsequence(nums: list[int]) -> int:
     """
     if nums is None:
         raise ValueError("Input array cannot be None")
-    
+
     if len(nums) == 0:
         return 0
 
@@ -61,6 +62,7 @@ def longest_arithmetic_subsequence(nums: list[int]) -> int:
 
 if __name__ == "__main__":
     import doctest
+
     doctest.testmod()
     # Sample test case
     nums = [3, 6, 9, 12]