bpo-20774: Add a JSON serializer to collections.deque

[lisroach]

PR for issue 20774, adding a JSON serializer to collections.deque.

https://bugs.python.org/issue20774

[mention-bot]

@lisroach, thanks for your PR! By analyzing the history of the files in this pull request, we identified @tiran, @benjaminp and @loewis to be potential reviewers.

[rhettinger]

Over this looks good. Can you please add some tests.

[Birne94]

Wouldn't you need to decrease the reference counter to mo and deque_type after using them?

[brettcannon]

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[sakurai-youhei]

For those who arrived here like me when searching quick solution to encode dqeue object into JSON; Below code (as per documentation) shall be good enough.

from collections import deque
from json import dumps, JSONEncoder

class JSONEncoderSupportingArbitraryIterators(JSONEncoder):
    def default(self, o):
        try:
            iterable = iter(o)
        except TypeError:
            pass
        else:
            return list(iterable)
        # Let the base class default method raise the TypeError
        return JSONEncoder.default(self, o)

dumps(deque(range(10)), cls=JSONEncoderSupportingArbitraryIterators)

[carlbordum]

@lisroach are you interested in writting the tests, or may I? :)

[lisroach]

Sorry, just realized I had this sitting for so long! @carlbordum feel free to add more tests if you think of them :)

[matrixise]

Maybe you could remove this blank line

[matrixise]

Why this line ?

[csabella]

@lisroach, should this pull request be closed based on the performance benchmarks mentioned on the bug tracker or were you still working on this change? Thanks!

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[erlend-aasland]

@lisroach, are you going to follow up this PR?

[kumaraditya303]

Closing because of lack of response and conflicts, feel free to reopen if you want to work on this.