Wrapper to assign futures to the correct event loop

Author: elacuesta

scrapy_playwright/__init__.py

@@ -1 +1,6 @@
 __version__ = "0.0.40"
+
+
+from ._utils import ensure_future  # noqa: F401
+from .handler import ScrapyPlaywrightDownloadHandler  # noqa: F401
+from .page import PageMethod  # noqa: F401

scrapy_playwright/_utils.py

@@ -129,10 +129,14 @@ async def _process_queue(cls) -> None:
             cls._coro_queue.task_done()
 
     @classmethod
-    def _deferred_from_coro(cls, coro) -> Deferred:
+    def _ensure_future(cls, coro: Awaitable) -> asyncio.Future:
         future: asyncio.Future = asyncio.Future()
         asyncio.run_coroutine_threadsafe(cls._coro_queue.put((coro, future)), cls._loop)
-        return scrapy.utils.defer.deferred_from_coro(future)
+        return future
+
+    @classmethod
+    def _deferred_from_coro(cls, coro: Awaitable) -> Deferred:
+        return scrapy.utils.defer.deferred_from_coro(cls._ensure_future(coro))
 
     @classmethod
     def start(cls, caller_id: int) -> None:
@@ -158,3 +162,24 @@ def stop(cls, caller_id: int) -> None:
             asyncio.run_coroutine_threadsafe(cls._coro_queue.join(), cls._loop)
             cls._loop.call_soon_threadsafe(cls._loop.stop)
             cls._thread.join()
+
+
+def ensure_future(coro: Awaitable) -> asyncio.Future:
+    """Wrap a coroutine in a Future assigned to the threaded event loop.
+
+    On windows, Playwright runs in an event loop of its own in a separate thread.
+    If Playwright coroutines are awaited directly, they are assigned to the main
+    thread's event loop, resulting in: "ValueError: The future belongs to a
+    different loop than the one specified as the loop argument"
+
+    Usage:
+    ```
+    from playwright.async_api import Page
+    from scrapy_playwright import ensure_future
+
+    async def parse(self, response):
+        page: Page = response.meta["playwright_page"]
+        await ensure_future(page.screenshot(path="example.png", full_page=True))
+    ```
+    """
+    return _ThreadedLoopAdapter._ensure_future(coro)