# 列表生成式
lst = []
for i in range(10):
    lst.append(i * 2)
print(lst)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# 相当于：
lst = [i * 2 for i in range(10)]
print(lst)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# 列表生成器：循环迭代，推断下一元素
lst = (i * 2 for i in range(10))
print(lst)
# <generator object <genexpr> at 0x0000000004200CF0>

"""生成器：
只用调用是才会生成相应的数据
只记录当前位置
只有一个__next__()
"""

# 菲波那切数列Fibonacci
def fib(max):  # 此时不能叫函数，应该叫生成器
    n = 0
    a, b = 0, 1
    while n < max:
        yield b  # 返回当前值，并保存当前状态
        a, b = b, a+b  # 同时赋值
        n = n+ 1
    return "异常消息"  # 输出异常信息

f = fib(10)
print("===")
print(f.__next__())  # 下一个值
print("===")
print(f.__next__())

print("==start loop==")
# for i in f:
#     print(i)
while True:
    try:
        g = next(f)
        print(g)
    except StopIteration as e:
        print("value of e :", e.value)
        break

"""OUT:
===
1
===
1
==start loop==
2
3
5
8
13
21
34
55
value of e : 异常消息
"""