Python 如何部分使用可迭代生成器（没有 `next`）？

Question

我有一个 class 充当可迭代生成器（根据），我想使用 for 循环部分使用它。

我不能使用 next（比如 Python -- consuming one generator inside various consumers），因为第一个部分消耗使用了一个只接受迭代器的库。如何从库函数停止的地方开始继续使用生成器？

（相关：Pause Python Generator, ）

class gen(): # 
    def __iter__(self):
        for i in range(20):
            yield i

# I want to partially consume in the first loop and finish in the second
my_gen_2 = gen()
for i in my_gen_2:  # imagine this is the internal implementation of the library function
    print(i)
    if i > 10:      # the real break condition is when iterfzf recieves user input
        break

for i in my_gen_2:  # i'd like to process the remaining elements instead of starting over
    print('p2', i)

# the confusion boils down to this
my_gen = gen()
for i in my_gen:
    print(i)    # prints 1 through 20 as expected
for i in my_gen:
    print('part two', i)    # prints something, even though the generator should have been "consumed"?

Answer 1

每次循环中的迭代生成器，都会得到一个新的迭代器。例如：

class gen(): # 
    def __init__(self):
        self.count = 0
    def __iter__(self):
        self.count += 1
        print("Hallo iter {0}".format(self.count))
        yield self.count

my_gen = gen()
>>> for i in my_gen:
...    pass
Hallo iter 1
>>> for i in my_gen:
...    pass
Hallo iter 2

如果您想使用旧的迭代器，只需使用 gen().__iter__()

>>> my_gen = gen().__iter__()
>>> for i in my_gen:
...    pass
Hallo iter 1
>>> for i in my_gen:
...    pass

Answer 2

正如@napuzba 指出的那样，__iter__ returns 每次使用时都是一个全新的生成器。相反，将状态存储在 self:

class gen():
    def __init__(self):
        self.count = 0
    def __iter__(self):
        while self.count < 20:
            self.count += 1
            yield self.count

Python 如何部分使用可迭代生成器（没有 `next`）？

Python how to partially consume an iterable generator (without `next`)?

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