diff --git a/python/0036-valid-sudoku.py b/python/0036-valid-sudoku.py
index c4ad694d8..f1324fc57 100644
--- a/python/0036-valid-sudoku.py
+++ b/python/0036-valid-sudoku.py
@@ -6,16 +6,17 @@ def isValidSudoku(self, board: List[List[str]]) -> bool:
 
         for r in range(9):
             for c in range(9):
-                if board[r][c] == ".":
+                num = board[r][c]
+                if num == ".":
                     continue
                 if (
-                    board[r][c] in rows[r]
-                    or board[r][c] in cols[c]
-                    or board[r][c] in squares[(r // 3, c // 3)]
+                    num in rows[r]
+                    or num in cols[c]
+                    or num in squares[(r // 3, c // 3)]
                 ):
                     return False
-                cols[c].add(board[r][c])
-                rows[r].add(board[r][c])
-                squares[(r // 3, c // 3)].add(board[r][c])
+                cols[c].add(num)
+                rows[r].add(num)
+                squares[(r // 3, c // 3)].add(num)
 
         return True