生成器

要创建一个generator，有很多种方法。第一种方法很简单，只要把一个列表生成式的[]改成()，就创建了一个generator：

https://www.liaoxuefeng.com/wiki/0014316089557264a6b348958f449949df42a6d3a2e542c000/0014317799226173f45ce40636141b6abc8424e12b5fb27000

>>> L = [x * x for x in range(10)]
>>> L
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
>>> g = (x * x for x in range(10))
>>> g
<generator object <genexpr> at 0x1022ef630>

一个生成器的例子：

def triangles():
    a=[1]
    yield [1]
    while 1:
        b=[1]
        for i,x in enumerate(a):
            if i==0:
                continue
            b.append(x+a[i-1])
        b.append(1)
        yield b
        a=b

n = 0
results = []
for t in triangles():
    print(t)
    results.append(t)
    n = n + 1
    if n == 10:
        break
if results == [
    [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]
]:
    print('测试通过!')
else:
    print('测试失败!')