不造理解的对不对

vv阿甘vv

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个人很迷惑，怎么也想不出来怎么写，看了下面同学们的回复，又在网上查询相关解释，现将个人理解写下来

输出杨辉三角如下：

[1] 
[1, 1] 
[1, 2, 1] 
[1, 3, 3, 1] 
[1, 4, 6, 4. 1] 
[1, 5, 10, 10, 5, 1] 
[1, 6, 15, 20, 15, 6, 1] 
[1, 7, 21, 35, 35, 21, 7, 1] 
[1, 8, 28, 56, 70, 56, 28, 8, 1] 
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]

代码实现如下


def triangles():
    L = [1]
    while True:
        yield L
        L.append(0)
        L = [L[i-1] + L[i] for i in range(len(L))]

n = 0
for m in triangles():
    print(m)
    n = n + 1
    if n == 10:
        break

解释下

L = [1]  # 定义一个只有一个值得list
yield L # 遇到yield就返回L ,此时返回第一行 [1]
L.append(0) # 给L添加个元素0，此时L = [1,0]
此时 L 里面有两个元素，len(L) = 2,range(len(L)) = range(2) = [0,1]
L = [L[i-1] + L[i] for i in range(len(L))]
  = [L[-1] + L[0],L[0] + L[1]]
  = [0 + 1, 1 + 0]
  = [1, 1]

### 此时yield 返回第二行 [1,1]

接下来看第三行

# 首先 L.append(0), L = [1, 1, 0]
# 那么 len(L) = 3, range(len(L)) = [0, 1, 2]

L = [L[i-1] + L[i] for i in range(len(L))]
  = [L[-1] + L[0], L[0] + L[1], L[1] + L[2]]
  = [0 + 1, 1 + 1, 1 + 0]
  = [1, 2, 1]
# 此时yield返回第三行 [1, 2, 1]

接下来第四行

# 首先L.append(0), 则L = [1, 2, 1, 0]
# 那么 len(L) = 4, range(len(L)) = [0, 1, 2, 3]

L = [L[i-1] + L[i] for i in range(len(L))]
  = [L[-1] + L[0], L[0] + L[1], L[1] + [2], L[2] + L[3]]
  = [0 + 1, 1 + 2, 2 + 1, 1 + 0]
  = [1, 3, 3, 1]