input: Write a function that prints out Pascal's triangle for a given number of rows. The function should accept an integer `n` as input and print the first `n` rows of Pascal's triangle. If `n` is less than 1, the function should return without printing anything.
  
  def pascal_triangle(n): 
      if n < 1:
          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) is None
  assert pascal_triangle(0) is None
  assert pascal_triangle(-3) is None
output: def pascal_triangle(n): 
      if n < 1:
          return
      trow = [1] 
      y = [0] 
      for x in range(n): 
          print(trow) 
          trow=[l+r for l,r in zip(trow + y, y + trow)]