python_Day4：杨辉三角，利用generator 输出

上个list元素两两相加等于下一个内部元素

def triangles(num):
    l = []
    if num == 1:
        l = [1]
        yield l
    else:
        l = [1]
        yield l
        l = [1,1]
        yield l
        while len(l) < num:
            new_l = []
            for i in range(len(l) - 1):
                n = l[i] + l[i + 1]
                new_l.append(n)
            new_l.insert(0, 1)
            new_l.append(1)
            l = new_l
            yield l
g = triangles(10)
for i in g:
    print(i)