initial commit

request_coalescing_py/coalescer.py

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+import asyncio
+from typing import Optional
+
+from request_coalescing_py.models import Item
+from request_coalescing_py.database import DatabaseRepo
+
+
+class CoalescingRepo:
+    def __init__(self, repo: DatabaseRepo):
+        self._repo = repo
+
+        self._queue = asyncio.Queue()
+        self._queued = {}  # map of item_id: future
+
+    async def get_by_id(self, item_id: int) -> "asyncio.Future[Optional[Item]]":
+        # Check if there is an already pending request for that item.
+        fut = self._queued.get(item_id)
+        if fut:
+            return fut
+        
+        # There is not a pending request.
+        fut = asyncio.get_event_loop().create_future()
+        self._queued[item_id] = fut
+        await self._queue.put(item_id)
+        return fut
+
+    async def process_queue(self) -> None:
+        while True:
+            item_id = await self._queue.get()
+            item = await self._repo.get_by_id(item_id)
+            self._queued[item_id].set_result(item)
+            del self._queued[item_id]
+            self._queue.task_done()