old_contents: def graph_dfs(matrix):
      rows, cols = len(matrix), len(matrix[0])
      visited = set()
      directions = ((0, 1), (0, -1), (1, 0), (-1, 0))
      def dfs(i, j):
          if (i, j) in visited:
              return
          visited.add((i, j))
          # Traverse neighbors.
          for direction in directions:
              next_i, next_j = i + direction[0], j + direction[1]
              if 0 <= next_i < rows and 0 <= next_j < cols: # Check boundary.
                  # Add any other checking here ^
                  dfs(next_i, next_j)
  
      for i in range(rows):
          for j in range(cols):
              dfs(i, j)
  
  # Follow up:
  # 1) Diagonal cells are considered neighbors
  # 2) View the matrix like Earth, right boundary is adjacent to the left boundary, top adjacent to left, etc.
  def graph_dfs_diagonals(matrix):
      rows, cols = len(matrix), len(matrix[0])
      visited = set()
      # Change 1: Add 4 more diagonal directions.
      directions = ((0, 1), (0, -1), (1, 0), (-1, 0), (-1, -1), (1, 1), (1, -1), (-1, 1))
      def dfs(i, j):
          if (i, j) in visited:
              return
          print(matrix[i][j])
          visited.add((i, j))
          for direction in directions:
              # Change 2: No more boundary, use modulo to allow traversal that exceed boundaries to wrap around.
              next_i, next_j = (i + direction[0] + rows) % rows, (j + direction[1] + cols) % cols
              dfs(next_i, next_j)
  
      for i in range(rows):
          for j in range(cols):
              dfs(i, j)
  
  graph_dfs([
      [1, 2, 3, 4],
      [5, 6, 7, 8],
      [9, 10, 11, 12],
  ])
  
new_contents: def graph_dfs(matrix):
      rows, cols = len(matrix), len(matrix[0])
      visited = set()
      directions = ((0, 1), (0, -1), (1, 0), (-1, 0))
      def dfs(i, j):
          if (i, j) in visited:
              return
          visited.add((i, j))
          # Traverse neighbors.
          for direction in directions:
              next_i, next_j = i + direction[0], j + direction[1]
              if 0 <= next_i < rows and 0 <= next_j < cols: # Check boundary.
                  # Add any other checking here ^
                  dfs(next_i, next_j)
  
      for i in range(rows):
          for j in range(cols):
              dfs(i, j)
  
  # Follow up:
  # 1) Diagonal cells are considered neighbors
  # 2) View the matrix like Earth, right boundary is adjacent to the left boundary, top adjacent to left, etc.
  def graph_dfs_diagonals_and_boundary_wrap(matrix):
      rows, cols = len(matrix), len(matrix[0])
      visited = set()
      # Change 1: Add 4 more diagonal directions.
      directions = ((0, 1), (0, -1), (1, 0), (-1, 0), (-1, -1), (1, 1), (1, -1), (-1, 1))
      def dfs(i, j):
          if (i, j) in visited:
              return
          print(matrix[i][j])
          visited.add((i, j))
          for direction in directions:
              # Change 2: No more boundary, use modulo to allow traversal that exceed boundaries to wrap around.
              next_i, next_j = (i + direction[0] + rows) % rows, (j + direction[1] + cols) % cols
              dfs(next_i, next_j)
  
      for i in range(rows):
          for j in range(cols):
              dfs(i, j)
  
  graph_dfs([
      [1, 2, 3, 4],
      [5, 6, 7, 8],
      [9, 10, 11, 12],
  ])
  
subject: Rename dfs extension function