python 迭代器、生成器

In [7]: L = [2, 3, 5, 7]
   ...: for x in L:
   ...:     print(x)
   ...: else:
   ...:     print(‘循环结束‘)
   ...: print("---------------")
   ...: it = iter(L)  # 从L中获取一个迭代器
   ...: while True:
   ...:     try:
   ...:         x = next(it)
   ...:         print(x)
   ...:     except StopIteration:
   ...:         print("循环结束")
   ...:         break
   ...:
2
3
5
7
循环结束
---------------
2
3
5
7
循环结束

In [9]: L = [2, 3, 5, 7]
   ...: it = iter(L)  # 用L对象返回能访问L的迭代器, it绑定迭代器
   ...: next(it)  # 2
   ...: next(it)  # 3
   ...: next(it)  # 5
   ...: next(it)  # 7
   ...: next(it)  # StopIteration 通知(没有数据)
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-9-b65817a9e736> in <module>
      5 next(it)  # 5
      6 next(it)  # 7
----> 7 next(it)  # StopIteration 通知(没有数据)

StopIteration:

In [10]:      

In [66]: def myyield():
    ...:     yield 2
    ...:     yield 3
    ...:     yield 5
    ...:     yield 7
    ...:     print("生成结束")
    ...:
    ...:
    ...: for x in myyield():
    ...:     print(x)
    ...:
2
3
5
7
生成结束

In [67]: def myyield():
    ...:     print("即将生成2")
    ...:     yield 2
    ...:     print("即将生成3")
    ...:     yield 3
    ...:     print("即将生成5")
    ...:     yield 5
    ...:     print("即将生成7")
    ...:     yield 7
    ...:     print("生成结束")
    ...:
    ...: gen = myyield()  # gen 绑定一个生成器对象
    ...: it = iter(gen)  # 用生成器返回一个迭代器
    ...:
    ...: # 从迭代器获取一个数据(此时生成器函数才开始执行)
    ...: print(next(it))
即将生成2
2

In [68]: print(next(it))
即将生成3
3

In [69]: print(next(it))
即将生成5
5

In [70]: print(next(it))
即将生成7
7

In [71]: print(next(it))
生成结束
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-71-4d0222393be1> in <module>
----> 1 print(next(it))

StopIteration:

In [72]:

# 用生成器函数生成一定范围内的自然数
def myinteger(n):
    i = 0  # 自然数从0开始
    while i < n:
        yield i
        i += 1

for x in myinteger(3):
    print(x)

In [21]: gen = (x ** 2 for x in range(1, 5))
    ...: it = iter(gen)
    ...: next(it)  # 1
Out[21]: 1

In [22]: next(it)
Out[22]: 4

In [23]: next(it)
Out[23]: 9

In [24]: next(it)
Out[24]: 16

In [25]: next(it)
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-25-bc1ab118995a> in <module>
----> 1 next(it)

StopIteration: