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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> </head>

asyncio

Scrapy supports :mod:`asyncio` natively. New projects created with :command:`startproject` have asyncio enabled by default, and you can use :mod:`asyncio` and :mod:`asyncio`-powered libraries in any :doc:`coroutine <coroutines>`.

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The rest of this page covers advanced topics. If you are starting a new project, no additional setup is needed.

Configuring the asyncio reactor

New projects generated with :command:`startproject` have the asyncio reactor configured by default. No manual setup is needed.

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The :setting:`TWISTED_REACTOR` setting controls which Twisted reactor Scrapy uses. Its default value is 'twisted.internet.asyncioreactor.AsyncioSelectorReactor', which enables :mod:`asyncio` support.

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If you are using :class:`~scrapy.crawler.AsyncCrawlerRunner` or :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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.. code-block:: python

    install_reactor("twisted.internet.asyncioreactor.AsyncioSelectorReactor")

Handling a pre-installed reactor

twisted.internet.reactor and some other Twisted imports install the default Twisted reactor as a side effect. Once a Twisted reactor is installed, it is not possible to switch to a different reactor at run time.

If you :ref:`configure the asyncio Twisted reactor <install-asyncio>` and, at run time, Scrapy complains that a different reactor is already installed, chances are you have some such imports in your code.

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You can usually fix the issue by moving those offending module-level Twisted imports to the method or function definitions where they are used. For example, if you have something like:

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.. code-block:: python

    from twisted.internet import reactor


    def my_function():
        reactor.callLater(...)

Switch to something like:

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.. code-block:: python

    def my_function():
        from twisted.internet import reactor

        reactor.callLater(...)

Alternatively, you can try to :ref:`manually install the asyncio reactor <install-asyncio>`, with :func:`~scrapy.utils.reactor.install_reactor`, before those imports happen.

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Integrating Deferred code and asyncio code

Coroutine functions can await on Deferreds by wrapping them into :class:`asyncio.Future` objects. 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 don't need to support reactors other than the default :class:`~twisted.internet.asyncioreactor.AsyncioSelectorReactor`, you can use :func:`~scrapy.utils.defer.deferred_to_future`, otherwise you should use :func:`~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 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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Coroutines and futures can be wrapped into Deferreds (for example, when a Scrapy API requires passing a Deferred to it) using the following helpers:

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.. autofunction:: scrapy.utils.defer.deferred_from_coro

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.. autofunction:: scrapy.utils.defer.deferred_f_from_coro_f

The following function helps with a reverse wrapping:

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.. autofunction:: scrapy.utils.defer.ensure_awaitable

Enforcing asyncio as a requirement

If you are writing a :ref:`component <topics-components>` that requires asyncio to work, use :func:`scrapy.utils.asyncio.is_asyncio_available` to :ref:`enforce it as a requirement <enforce-component-requirements>`. For example:

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.. code-block:: python

    from scrapy.utils.asyncio import is_asyncio_available


    class MyComponent:
        def __init__(self):
            if not is_asyncio_available():
                raise ValueError(
                    f"{MyComponent.__qualname__} requires the asyncio support. "
                    f"Make sure you have configured the asyncio reactor in the "
                    f"TWISTED_REACTOR setting. See the asyncio documentation "
                    f"of Scrapy for more information."
                )

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.. autofunction:: scrapy.utils.asyncio.is_asyncio_available

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.. autofunction:: scrapy.utils.reactor.is_asyncio_reactor_installed

Using Scrapy without a Twisted reactor

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.. versionadded:: 2.15.0

Warning

This is currently experimental and may not be suitable for production use.

It's possible to use Scrapy without installing a Twisted reactor at all, by setting the :setting:`TWISTED_REACTOR_ENABLED` setting to False. In this mode Scrapy will use the asyncio event loop directly, and most of the Scrapy functionality will work in the same way.

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Doing this provides several benefits in certain use cases:

Limitations

As some Scrapy features and components require a reactor, they don't work and are disabled without it. Replacements that don't require a reactor may be added in future Scrapy versions. The following features are not available:

Note that importing Twisted modules and, among other things, creating and using :class:`~twisted.internet.defer.Deferred` objects doesn't require a reactor, so code that uses :class:`~twisted.internet.defer.Deferred`, :class:`~twisted.python.failure.Failure` and some other Twisted APIs will not necessarily stop working.

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Other differences

When :setting:`TWISTED_REACTOR_ENABLED` is set to False, Scrapy will change the defaults of some other settings:

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Thus, :class:`~scrapy.core.downloader.handlers._httpx.HttpxDownloadHandler` is used by default for making HTTP(S) requests. Please refer to its documentation for its differences and limitations compared to :class:`~scrapy.core.downloader.handlers.http11.HTTP11DownloadHandler`.

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Additionally, :class:`~scrapy.crawler.AsyncCrawlerProcess` will install a :term:`meta path finder` that prevents :mod:`twisted.internet.reactor` from being imported.

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Adding support to existing code

Code that doesn't directly use Twisted APIs or APIs that depend on Twisted ones doesn't need special support for running without a reactor.

Here are some examples of APIs and patterns that need a replacement:

Scrapy provides unified helpers for some of these examples:

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.. autofunction:: scrapy.utils.asyncio.call_later

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.. autofunction:: scrapy.utils.asyncio.create_looping_call

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.. autoclass:: scrapy.utils.asyncio.AsyncioLoopingCall

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.. autofunction:: scrapy.utils.asyncio.run_in_thread

If your code needs to know whether the reactor is available, you can either check for the value of the :setting:`TWISTED_REACTOR_ENABLED` setting (you need access to the :class:`~scrapy.crawler.Crawler` instance to do this) or use the following function:

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.. autofunction:: scrapy.utils.reactorless.is_reactorless

In general, code that doesn't use the reactor (directly or indirectly) can be used unmodified both with the asyncio reactor and without a reactor. This includes code that converts Deferreds to futures and vice versa as described in :ref:`asyncio-await-dfd`.

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Troubleshooting

ImportError: Import of twisted.internet.reactor is forbidden when running without a Twisted reactor [...]: Scrapy is configured to run without a reactor, but some code imported :mod:`twisted.internet.reactor`, most likely because that code needs a reactor to be used. You need to stop using this code or set :setting:`TWISTED_REACTOR_ENABLED` back to True. It's also possible that the reactor isn't really needed but was installed due to the problem described in :ref:`asyncio-preinstalled-reactor`, in which case it should be enough to fix the problematic imports.

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RuntimeError: TWISTED_REACTOR_ENABLED is False but a Twisted reactor is installed: Scrapy is configured to run without a reactor, but a reactor is already installed before the Scrapy code is executed. If you are trying to set :setting:`TWISTED_REACTOR_ENABLED` via :ref:`per-spider settings <spider-settings>`, it's currently unsupported.

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RuntimeError: We expected a Twisted reactor to be installed but it isn't: Scrapy is configured to run with a reactor and not to install one, but a reactor wasn't installed before the Scrapy code is executed. If you are trying to set :setting:`TWISTED_REACTOR_ENABLED` via :ref:`per-spider settings <spider-settings>`, it's currently unsupported.

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RuntimeError: <class> doesn't support TWISTED_REACTOR_ENABLED=False: The listed class cannot be used with :setting:`TWISTED_REACTOR_ENABLED` set to False. There may be a replacement in the :ref:`documentation above <asyncio-without-reactor>` or the documentation of the affected class.

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Windows-specific notes

The Windows implementation of :mod:`asyncio` can use two event loop implementations, :class:`~asyncio.ProactorEventLoop` (default) and :class:`~asyncio.SelectorEventLoop`. However, only :class:`~asyncio.SelectorEventLoop` works with Twisted.

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Scrapy changes the event loop class to :class:`~asyncio.SelectorEventLoop` automatically when installing the asyncio reactor.

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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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Note

This problem doesn't apply when not using the reactor, see :ref:`asyncio-without-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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Switching to a non-asyncio reactor

If for some reason your code doesn't work with the asyncio reactor, you can use a different reactor by setting the :setting:`TWISTED_REACTOR` setting to its import path (e.g. 'twisted.internet.epollreactor.EPollReactor') or to None, which will use the default reactor for your platform. If you are using :class:`~scrapy.crawler.AsyncCrawlerRunner` or :class:`~scrapy.crawler.AsyncCrawlerProcess` you also need to switch to their Deferred-based counterparts: :class:`~scrapy.crawler.CrawlerRunner` or :class:`~scrapy.crawler.CrawlerProcess` respectively.

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