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🛑 A rate limited wrapper for Python's thread safe queues.

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# 🛑 RateLimitQueue

A rate limited wrapper for Python's thread safe queues.

Some external APIs have rate limits that allow faster-than-consecutive queries, e.g. if the rate limit is very high or the API response is quite slow. To make the most of the API, the best option is often to make API calls from multiple threads. Then you can put the requests or URLs to call in a `queue.Queue` and have the threads consume the URLs as they make the calls. However, you still have to make sure that the total calls from all your threads don't exceed the rate limit, which requires some nontrivial coordination.

The `ratelimitqueue` package extends the three built-in Python queues from from `queue` package - `Queue`, `LifoQueue`, and `PriorityQueue` - with configurable, rate limited counterparts. Specifically, the `get()` method is rate limited across all threads so that workers can safely consume from the queue in an unlimited loop, and putting the items in the queue doesn't need to require blocking the main thread.

## 🔌 Installation

To get started, install `ratelimitqueue` with `pip`:

```bash
pip install ratelimitqueue
```

## 🌟 Examples

The most basic usage is rate limiting calls in the main thread by pre-loading a `RateLimitQueue`. For a rate limit of 2 calls per second:

```python
rlq = ratelimitqueue.RateLimitQueue(calls=2, per=1)

# load up the queue
for url in LIST_OF_URLS:
    rlq.put(url)

# make the calls
while rlq.qsize() > 0:
    url = rlq.get()
    make_call_to_api(url)
    rlq.task_done()

```

A more typical use case would be to have a pool of workers making API calls in parallel:

```python
rlq = ratelimitqueue.RateLimitQueue(calls=3, per=2)
n_workers = 4

def worker(rlq):
    """Makes API calls on URLs from queue until it is empty."""
    while rlq.qsize() > 0:
        url = rlq.get()
        make_call_to_slow_api(url)
        rlq.task_done()

# load up the queue
for url in LIST_OF_URLS:
    rlq.put(url)

# make the calls
with multiprocessing.dummy.Pool(n_workers, worker, (rlq,)) as pool:
    rlq.join()

```

Working versions of these examples can be found in the [examples directory](https://github.com/JohnPaton/ratelimitqueue/tree/master/examples).

ratelimitqueue

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