3.12.3 introduces a breaking change when using DjangoRedis 4.12.1

[Bradleywboggs]

3.12.3 introduces a breaking change when using DjangoRedis 4.12.1

For a request without a cached throttling history, the change in the class SimpleRateThrottle,
at rest_framework/throttling.py::124:
self.history = self.cache.get(self.key, deque())
causes a TypeError to be raised in the same class in the throttle_success method specifically at line 141:
self.cache.set(self.key, self.history, self.duration

The root of the problem is that DjangoRedis json-serializes the value before inserting into the cache, but deques are not json serializable. So the solution would appear to be to cast the value as a deque on get and as a list onset or just keep the history as a list.
e.g.

self.history = deque(self.cache.get(self.key, []))
....
self.cache.set(self.key, list(self.history), self.duration)

@tomchristie

[tomchristie]

Good example of how even innocuous looking changes have an attached risk.

---

🙂 - "Hey, PR #7849 for keeping the history as a deque instead of list. Makes sense, right?"
"...Um, I guess, yup. There might be some risks we've not foreseen." - 🤔
😀 - "Can't see any."
"No me neither. Okay, I guess this may as well go in." - 👍

... (not much) time passes ...

<unforeseen risks become surfaced> 😑

---

Anyways, just another data point for erring on the side of keeping code churn to an absolute minimum wherever possible.

I'll go ahead and revert this, and likely roll a new release.

[Bradleywboggs]

Haha! I totally get it! Thanks for the quick response.