diff --git a/conftest.py b/conftest.py index 05b4ccdad..117087790 100644 --- a/conftest.py +++ b/conftest.py @@ -75,6 +75,12 @@ def only_asyncio(request, reactor_pytest): pytest.skip('This test is only run with --reactor=asyncio') +@pytest.fixture(autouse=True) +def only_not_asyncio(request, reactor_pytest): + if request.node.get_closest_marker('only_not_asyncio') and reactor_pytest == 'asyncio': + pytest.skip('This test is only run without --reactor=asyncio') + + def pytest_configure(config): if config.getoption("--reactor") == "asyncio": install_reactor("twisted.internet.asyncioreactor.AsyncioSelectorReactor") diff --git a/docs/topics/asyncio.rst b/docs/topics/asyncio.rst index 82c5f271f..28241ae24 100644 --- a/docs/topics/asyncio.rst +++ b/docs/topics/asyncio.rst @@ -39,5 +39,22 @@ 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. +.. _asyncio-await-dfd: +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: + +.. autofunction:: scrapy.utils.defer.deferred_to_future +.. 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. diff --git a/docs/topics/coroutines.rst b/docs/topics/coroutines.rst index 0904637b0..2aef755c7 100644 --- a/docs/topics/coroutines.rst +++ b/docs/topics/coroutines.rst @@ -75,23 +75,28 @@ coroutines, functions that return Deferreds and functions that return :term:`awaitable objects ` such as :class:`~asyncio.Future`. This means you can use many useful Python libraries providing such code:: - class MySpider(Spider): + class MySpiderDeferred(Spider): # ... - async def parse_with_deferred(self, response): + async def parse(self, response): additional_response = await treq.get('https://additional.url') additional_data = await treq.content(additional_response) # ... use response and additional_data to yield items and requests - async def parse_with_asyncio(self, response): + class MySpiderAsyncio(Spider): + # ... + async def parse(self, response): async with aiohttp.ClientSession() as session: async with session.get('https://additional.url') as additional_response: - additional_data = await r.text() + additional_data = await additional_response.text() # ... use response and additional_data to yield items and requests .. note:: Many libraries that use coroutines, such as `aio-libs`_, require the :mod:`asyncio` loop and to use them you need to :doc:`enable asyncio support in Scrapy`. +.. note:: If you want to ``await`` on Deferreds while using the asyncio reactor, + you need to :ref:`wrap them`. + Common use cases for asynchronous code include: * requesting data from websites, databases and other services (in callbacks, diff --git a/docs/topics/item-pipeline.rst b/docs/topics/item-pipeline.rst index 5351a2293..391751364 100644 --- a/docs/topics/item-pipeline.rst +++ b/docs/topics/item-pipeline.rst @@ -190,6 +190,8 @@ item. import scrapy from itemadapter import ItemAdapter + from scrapy.utils.defer import maybe_deferred_to_future + class ScreenshotPipeline: """Pipeline that uses Splash to render screenshot of @@ -202,7 +204,7 @@ item. encoded_item_url = quote(adapter["url"]) screenshot_url = self.SPLASH_URL.format(encoded_item_url) request = scrapy.Request(screenshot_url) - response = await spider.crawler.engine.download(request, spider) + response = await maybe_deferred_to_future(spider.crawler.engine.download(request, spider)) if response.status != 200: # Error happened, return item. diff --git a/pytest.ini b/pytest.ini index 6de08c78d..fa5d6b34f 100644 --- a/pytest.ini +++ b/pytest.ini @@ -20,5 +20,6 @@ addopts = --ignore=docs/utils markers = only_asyncio: marks tests as only enabled when --reactor=asyncio is passed + only_not_asyncio: marks tests as only enabled when --reactor=asyncio is not passed filterwarnings= ignore::DeprecationWarning:twisted.web.test.test_webclient diff --git a/scrapy/utils/defer.py b/scrapy/utils/defer.py index b02bfdccb..d7adc0a77 100644 --- a/scrapy/utils/defer.py +++ b/scrapy/utils/defer.py @@ -3,9 +3,16 @@ Helper functions for dealing with Twisted deferreds """ import asyncio import inspect -from collections.abc import Coroutine +from asyncio import Future from functools import wraps -from typing import Any, Callable, Generator, Iterable +from typing import ( + Any, + Callable, + Coroutine, + Generator, + Iterable, + Union +) from twisted.internet import defer from twisted.internet.defer import Deferred, DeferredList, ensureDeferred @@ -171,3 +178,55 @@ def maybeDeferred_coro(f: Callable, *args, **kw) -> Deferred: return defer.fail(result) else: return defer.succeed(result) + + +def deferred_to_future(d: Deferred) -> Future: + """ + .. versionadded:: VERSION + + Return an :class:`asyncio.Future` object that wraps *d*. + + When :ref:`using the asyncio reactor `, you cannot await + on :class:`~twisted.internet.defer.Deferred` objects from :ref:`Scrapy + callables defined as coroutines `, you can only await on + ``Future`` objects. Wrapping ``Deferred`` objects into ``Future`` objects + allows you to wait on them:: + + class MySpider(Spider): + ... + async def parse(self, response): + d = treq.get('https://example.com/additional') + additional_response = await deferred_to_future(d) + """ + return d.asFuture(asyncio.get_event_loop()) + + +def maybe_deferred_to_future(d: Deferred) -> Union[Deferred, Future]: + """ + .. versionadded:: VERSION + + Return *d* as an object that can be awaited from a :ref:`Scrapy callable + defined as a coroutine `. + + What you can await in Scrapy callables defined as coroutines depends on the + value of :setting:`TWISTED_REACTOR`: + + - When not using the asyncio reactor, you can only await on + :class:`~twisted.internet.defer.Deferred` objects. + + - When :ref:`using the asyncio reactor `, you can only + await on :class:`asyncio.Future` objects. + + If you want to write code that uses ``Deferred`` objects but works with any + reactor, use this function on all ``Deferred`` objects:: + + class MySpider(Spider): + ... + async def parse(self, response): + d = treq.get('https://example.com/additional') + extra_response = await maybe_deferred_to_future(d) + """ + if not is_asyncio_reactor_installed(): + return d + else: + return deferred_to_future(d) diff --git a/tests/test_pipelines.py b/tests/test_pipelines.py index ff3af9a74..8e432b913 100644 --- a/tests/test_pipelines.py +++ b/tests/test_pipelines.py @@ -6,6 +6,7 @@ from twisted.internet.defer import Deferred from twisted.trial import unittest from scrapy import Spider, signals, Request +from scrapy.utils.defer import maybe_deferred_to_future, deferred_to_future from scrapy.utils.test import get_crawler, get_from_asyncio_queue from tests.mockserver import MockServer @@ -31,18 +32,38 @@ class DeferredPipeline: class AsyncDefPipeline: async def process_item(self, item, spider): - await defer.succeed(42) + d = Deferred() + from twisted.internet import reactor + reactor.callLater(0, d.callback, None) + await maybe_deferred_to_future(d) item['pipeline_passed'] = True return item class AsyncDefAsyncioPipeline: async def process_item(self, item, spider): + d = Deferred() + from twisted.internet import reactor + reactor.callLater(0, d.callback, None) + await deferred_to_future(d) await asyncio.sleep(0.2) item['pipeline_passed'] = await get_from_asyncio_queue(True) return item +class AsyncDefNotAsyncioPipeline: + async def process_item(self, item, spider): + d1 = Deferred() + from twisted.internet import reactor + reactor.callLater(0, d1.callback, None) + await d1 + d2 = Deferred() + reactor.callLater(0, d2.callback, None) + await maybe_deferred_to_future(d2) + item['pipeline_passed'] = True + return item + + class ItemSpider(Spider): name = 'itemspider' @@ -99,3 +120,10 @@ class PipelineTestCase(unittest.TestCase): crawler = self._create_crawler(AsyncDefAsyncioPipeline) yield crawler.crawl(mockserver=self.mockserver) self.assertEqual(len(self.items), 1) + + @mark.only_not_asyncio() + @defer.inlineCallbacks + def test_asyncdef_not_asyncio_pipeline(self): + crawler = self._create_crawler(AsyncDefNotAsyncioPipeline) + yield crawler.crawl(mockserver=self.mockserver) + self.assertEqual(len(self.items), 1)