习题14:建一个塔

[
  '     *     ', 
  '    ***    ', 
  '   *****   ', 
  '  *******  ', 
  ' ********* ', 
  '***********'
]

def make_tower(n_floors):
    l = []
    for i in range(n_floors):
        stars = '*'*(2*i + 1)
        spaces = ' '*(n_floors-k)
        l.append(spaces+stars+spaces)
    return l