input: Write a function that prints out the Pascal's triangle for a given number of rows. The function should take an integer `n` as input, which represents the number of rows to print. If `n` is 0 or negative, the function should return without printing anything. The function should use a list to generate the next row of the triangle based on the current row, and it should print each row as a list.
  
  def pascal_triangle(n): 
      if n <= 0:
          return
      trow = [1] 
      y = [0] 
      for x in range(n): 
          print(trow) 
          trow=[l+r for l,r in zip(trow + y, y + trow)] 
  
  assert pascal_triangle(5)==None
  assert pascal_triangle(0)==None
  assert pascal_triangle(-3)==None
output: def pascal_triangle(n): 
      if n <= 0:
          return
      trow = [1] 
      y = [0] 
      for x in range(n): 
          print(trow) 
          trow=[l+r for l,r in zip(trow + y, y + trow)]