Write a python generator to generate a code example of Yang Hui's triangle

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#生成器生成展示杨辉三角
#原理是在一个2维数组里展示杨辉三角，空的地方用0，输出时，转化为' '
def yang(line):
  n,leng=0,2*line - 1
  f_list = list(range(leng+2)) #预先分配，insert初始胡会拖慢速度，最底下一行，左右也有1个空格
  #全部初始化为0
  for i,v in enumerate(f_list):
    f_list[v] = 0
  ZEROLIST = f_list[:] #预留一个全零的数组
  f_list[leng//2] = 1 #初始的第一行
  re_list =f_list[:]
  n=0
  while n < line:
    n = n+1
    yield re_list
    f_list,re_list = re_list[:],ZEROLIST[:]
    start = leng//2-n #计算一行中第一个1的位置
    end = start + 2*n #计算一行中最后一个1的位置
    while start <= end:
      re_list[start] = f_list[start - 1] + f_list[start+1] #不管是不是1，该位置的数字，都是上一行该位置的左右两个数的和
      start = start + 1
  return &#39;done&#39;

def printList(L):
  n = 0
  p_str = &#39;&#39;
  for value in L:
    ch = str(value)
    if value == 0:
      ch = &#39; &#39;
    p_str = p_str + ch
  print(p_str)

for value in yang(8):
  printList(value)

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