input: Write a function to print Pascal's triangle for a given number of rows. If the number of rows is greater than or equal to 1, the function should print each row of the triangle. If the number of rows is less than 1, the function should do nothing.
  def pascal_triangle(n): 
      trow = [1] 
      y = [0] 
      for x in range(max(n, 0)): 
          print(trow) 
          trow=[l+r for l,r in zip(trow + y, y + trow)] 
  
  assert pascal_triangle(5)
  assert pascal_triangle(0)
  assert pascal_triangle(3)
  assert pascal_triangle(-1)
  assert pascal_triangle(1)
output: def pascal_triangle(n): 
      trow = [1] 
      y = [0] 
      for x in range(max(n, 0)): 
          print(trow) 
          trow=[l+r for l,r in zip(trow + y, y + trow)]