input: Write a function to print out Pascal's triangle for a given number of rows. The function should return nothing, it should only print the rows of the triangle. If the given number of rows is 0 or less, it should not print anything.
  assert pascal_triangle(5)==None
  assert pascal_triangle(0)==None
  assert pascal_triangle(-3)==None
  assert pascal_triangle(3)==None
  assert pascal_triangle(1)==None
output: def pascal_triangle(n):
      if n <= 0:
          return
      for line in range(1, n + 1):
          C = 1
          for i in range(1, line + 1):
              print(C, end=" ")
              C = C * (line - i) // i
          print()