3.3 KiB
asyncio
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.. versionadded:: 2.0
Scrapy has partial support for :mod:`asyncio`. After you :ref:`install the asyncio reactor <install-asyncio>`, you may use :mod:`asyncio` and :mod:`asyncio`-powered libraries in any :doc:`coroutine <coroutines>`.
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Unknown interpreted text role "doc".Installing the asyncio reactor
To enable :mod:`asyncio` support, set the :setting:`TWISTED_REACTOR` setting to 'twisted.internet.asyncioreactor.AsyncioSelectorReactor'.
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Unknown interpreted text role "setting".If you are using :class:`~scrapy.crawler.CrawlerRunner`, you also need to install the :class:`~twisted.internet.asyncioreactor.AsyncioSelectorReactor` reactor manually. You can do that using :func:`~scrapy.utils.reactor.install_reactor`:
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Using custom asyncio loops
You can also use custom asyncio event loops with the asyncio reactor. Set the :setting:`ASYNCIO_EVENT_LOOP` setting to the import path of the desired event loop class to use it instead of the default asyncio event loop.
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Unknown interpreted text role "setting".Windows-specific notes
The Windows implementation of :mod:`asyncio` can use two event loop implementations: :class:`~asyncio.SelectorEventLoop` (default before Python 3.8, required when using Twisted) and :class:`~asyncio.ProactorEventLoop` (default since Python 3.8, cannot work with Twisted). So on Python 3.8+ the event loop class needs to be changed. Scrapy since VERSION does this automatically when you change the :setting:`TWISTED_REACTOR` setting or call :func:`~scrapy.utils.reactor.install_reactor`, but if you install the reactor by other means or use an older Scrapy version you need to call the following code before installing the reactor:
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Unknown interpreted text role "func".import asyncio asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
You can put this in the same function that installs the reactor, if you do that yourself, or in some code that runs before the reactor is installed, e.g. settings.py.
Note
Other libraries you use may require :class:`~asyncio.ProactorEventLoop`, e.g. because it supports subprocesses (this is the case with playwright), so you cannot use them together with Scrapy on Windows (but you should be able to use them on WSL or native Linux).
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Unknown interpreted text role "class".Awaiting on Deferreds
When the asyncio reactor isn't installed, you can await on Deferreds in the coroutines directly. When it is installed, this is not possible anymore, due to specifics of the Scrapy coroutine integration (the coroutines are wrapped into :class:`asyncio.Future` objects, not into :class:`~twisted.internet.defer.Deferred` directly), and you need to wrap them into Futures. Scrapy provides two helpers for this:
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.. autofunction:: scrapy.utils.defer.deferred_to_future
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.. autofunction:: scrapy.utils.defer.maybe_deferred_to_future
Tip
If you need to use these functions in code that aims to be compatible with lower versions of Scrapy that do not provide these functions, down to Scrapy 2.0 (earlier versions do not support :mod:`asyncio`), you can copy the implementation of these functions into your own code.
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