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