scrapy-poet documentation

scrapy-poet allows to use web-poet Page Objects with Scrapy.

web-poet defines a standard for writing reusable and portable extraction and crawling code; please check its docs to learn more.

By using scrapy-poet you’ll be organizing the spider code in a different way, which separates extraction and crawling logic from the I/O, and from the Scrapy implementation details as well. It makes the code more testable and reusable. Furthermore, it opens the door to create generic spider code that works across sites. Integrating a new site in the spider is then just a matter of write a bunch of Page Objects for it.

scrapy-poet also provides a way to integrate third-party APIs (like Splash and AutoExtract) with the spider, without losing testability and reusability. Concrete integrations are not provided by web-poet, but scrapy-poet makes them possbile.

To get started, see Installation and Scrapy Tutorial.

License is BSD 3-clause.

Installation

Installing scrapy-poet

scrapy-poet is a Scrapy extension that runs on Python 3.8 and above.

If you’re already familiar with installation of Python packages, you can install scrapy-poet and its dependencies from PyPI with:

pip install scrapy-poet

Scrapy 2.6.0 or above is required and it has to be installed separately.

Configuring the project

To use scrapy-poet, enable its middlewares in the settings.py file of your Scrapy project:

DOWNLOADER_MIDDLEWARES = {
    "scrapy_poet.InjectionMiddleware": 543,
    "scrapy.downloadermiddlewares.stats.DownloaderStats": None,
    "scrapy_poet.DownloaderStatsMiddleware": 850,
}
SPIDER_MIDDLEWARES = {
    "scrapy_poet.RetryMiddleware": 275,
}
REQUEST_FINGERPRINTER_CLASS = "scrapy_poet.ScrapyPoetRequestFingerprinter"

Things that are good to know

scrapy-poet is written in pure Python and depends on a few key Python packages (among others):

• web-poet, core library used for Page Object pattern

• andi, provides annotation-based dependency injection

• parsel, responsible for css and xpath selectors

Basic Tutorial

In this tutorial, we’ll assume that scrapy-poet is already installed on your system. If that’s not the case, see Installation.

Note

This tutorial can be followed without reading web-poet docs, but for a better understanding it is highly recommended to check them first.

We are going to scrape books.toscrape.com, a website that lists books from famous authors.

This tutorial will walk you through these tasks:

1. Writing a spider to crawl a site and extract data

2. Separating extraction logic from the spider

3. Configuring Scrapy project to use scrapy-poet

4. Changing spider to make use of our extraction logic

If you’re not already familiar with Scrapy, and want to learn it quickly, the Scrapy Tutorial is a good resource.

Creating a spider

Create a new Scrapy project and add a new spider to it. This spider will be called books and it will crawl and extract data from a target website.

import scrapy


class BooksSpider(scrapy.Spider):
    """Crawl and extract books data"""

    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        """Discover book links and follow them"""
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    def parse_book(self, response):
        """Extract data from book pages"""
        yield {
            "url": response.url,
            "name": response.css("title::text").get(),
        }

Separating extraction logic

Let’s create our first Page Object by moving extraction logic out of the spider class.

from web_poet.pages import WebPage


class BookPage(WebPage):
    """Individual book page on books.toscrape.com website, e.g.
    http://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html
    """

    def to_item(self):
        """Convert page into an item"""
        return {
            "url": self.url,
            "name": self.css("title::text").get(),
        }

Now we have a BookPage class that implements the to_item method. This class contains all logic necessary for extracting an item from an individual book page like http://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html, and nothing else. In particular, BookPage is now independent of Scrapy, and is not doing any I/O.

If we want, we can organize code in a different way, and e.g. extract a property from the to_item method:

from web_poet.pages import WebPage


class BookPage(WebPage):
    """Individual book page on books.toscrape.com website"""

    @property
    def title(self):
        """Book page title"""
        return self.css("title::text").get()

    def to_item(self):
        return {
            "url": self.url,
            "name": self.title,
        }

The BookPage class we created can be used without scrapy-poet, and even without Scrapy (note that imports were from web_poet so far). scrapy-poet makes it easy to use web-poet Page Objects (such as BookPage) in Scrapy spiders.

See the Installation page on how to install and configure scrapy-poet in your project.

Changing spider

To use the newly created BookPage class in the spider, change the parse_book method as follows:

class BooksSpider(scrapy.Spider):
    # ...
    def parse_book(self, response, book_page: BookPage):
        """Extract data from book pages"""
        yield book_page.to_item()

parse_book method now has a type annotated argument called book_page. scrapy-poet detects this and makes sure a BookPage instance is created and passed to the callback.

The full spider code would be looking like this:

import scrapy


class BooksSpider(scrapy.Spider):
    """Crawl and extract books data"""

    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        """Discover book links and follow them"""
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    def parse_book(self, response, book_page: BookPage):
        """Extract data from book pages"""
        yield book_page.to_item()

You might have noticed that parse_book is quite simple; it’s just returning the result of the to_item method call. We could use callback_for() helper to reduce the boilerplate.

import scrapy
from scrapy_poet import callback_for


class BooksSpider(scrapy.Spider):
    """Crawl and extract books data"""

    name = "books"
    start_urls = ["http://books.toscrape.com/"]
    parse_book = callback_for(BookPage)

    def parse(self, response):
        """Discovers book links and follows them"""
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

Note

You can also write something like response.follow_all(links, callback_for(BookPage)), without creating an attribute, but currently it won’t work with Scrapy disk queues.

Tip

callback_for() also supports async generators. So if we have the following:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    async def parse_book(self, response: DummyResponse, page: BookPage):
        yield await page.to_item()

It could be turned into:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    parse_book = callback_for(BookPage)

This is useful when the Page Objects uses additional requests, which rely heavily on async/await syntax. More info on this in this tutorial section: Additional Requests.

Final result

At the end of our job, the spider should look like this:

import scrapy
from web_poet.pages import WebPage
from scrapy_poet import callback_for


class BookPage(WebPage):
    """Individual book page on books.toscrape.com website, e.g.
    http://books.toscrape.com/catalogue/a-light-in-the-attic_1000/index.html
    """

    def to_item(self):
        return {
            "url": self.url,
            "name": self.css("title::text").get(),
        }


class BooksSpider(scrapy.Spider):
    """Crawl and extract books data"""

    name = "books"
    start_urls = ["http://books.toscrape.com/"]
    parse_book = callback_for(BookPage)  # extract items from book pages

    def parse(self, response):
        """Discover book links and follow them"""
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

It now looks similar to the original spider, but the item extraction logic is separated from the spider.

Single spider - multiple sites

We have seen that using Page Objects is a great way to isolate the extraction logic from the crawling logic. As a side effect, it is now pretty easy to create a generic spider with a common crawling logic that works across different sites. The unique missing requirement is to be able to configure different Page Objects for different sites, because the extraction logic surely changes from site to site. This is exactly the functionality that overrides provides.

Note that the crawling logic of the BooksSpider is pretty simple and straightforward:

1. Extract all books URLs from the listing page

2. For each book URL found in the step 1, fetch the page and extract the resultant item

This logic should work without any change for different books sites because having pages with lists of books and then detail pages with the individual book is such a common way of structuring sites.

Let’s refactor the spider presented in the former section so that it also supports extracting books from the page bookpage.com/reviews as well.

The steps to follow are:

1. Make our spider generic: move the remaining extraction code from the spider to a Page Object

2. Configure overrides for Books to Scrape

3. Add support for another site (Book Page site)

Making the spider generic

This is almost done. The book extraction logic has been already moved to the BookPage Page Object, but extraction logic to obtain the list of URL to books is already present in the parse method. It must be moved to its own Page Object:

from web_poet.pages import WebPage


class BookListPage(WebPage):

    def book_urls(self):
        return self.css(".image_container a")

Let’s adapt the spider to use this new Page Object:

class BooksSpider(scrapy.Spider):
    name = "books_spider"
    parse_book = callback_for(BookPage)  # extract items from book pages

    def start_requests(self):
        yield scrapy.Request("http://books.toscrape.com/", self.parse)

    def parse(self, response, page: BookListPage):
        yield from response.follow_all(page.book_urls(), self.parse_book)

Warning

We could’ve defined our spider as:

class BooksSpider(scrapy.Spider):
    name = "books_spider"
    start_urls = ["http://books.toscrape.com/"]
    parse_book = callback_for(BookPage)  # extract items from book pages

    def parse(self, response, page: BookListPage):
        yield from response.follow_all(page.book_urls(), self.parse_book)

However, this would result in the following warning message:

A request has been encountered with callback=None which defaults to the parse() method. On such cases, annotated dependencies in the parse() method won’t be built by scrapy-poet. However, if the request has callback=parse, the annotated dependencies will be built.

This means that page isn’t injected into the parse() method, leading to this error:

TypeError: parse() missing 1 required positional argument: ‘page’

This stems from the fact that using start_urls would use the predefined start_requests() method wherein scrapy.Request has callback=None.

One way to avoid this is to always declare the callback in scrapy.Request, just like in the original example.

See the Pitfalls section for more information.

All the extraction logic that is specific to the site is now responsibility of the Page Objects. As a result, the spider is now site-agnostic and will work providing that the Page Objects do their work.

In fact, the spider only responsibility becomes expressing the crawling strategy: “fetch a list of item URLs, follow them, and extract the resultant items”. The code gets clearer and simpler.

Configure overrides for Books to Scrape

It is convenient to create bases classes for the Page Objects given that we are going to have several implementations of the same Page Object (one per each site). The following code snippet introduces such base classes and refactors the existing Page Objects as subclasses of them:

from web_poet.pages import WebPage


# ------ Base page objects ------

class BookListPage(WebPage):

    def book_urls(self):
        return []


class BookPage(WebPage):

    def to_item(self):
        return None

# ------ Concrete page objects for books.toscrape.com (BTS) ------

class BTSBookListPage(BookListPage):

    def book_urls(self):
        return self.css(".image_container a::attr(href)").getall()


class BTSBookPage(BookPage):

    def to_item(self):
        return {
            "url": self.url,
            "name": self.css("title::text").get(),
        }

The spider won’t work anymore after the change. The reason is that it is using the new base Page Objects and they are empty. Let’s fix it by instructing scrapy-poet to use the Books To Scrape (BTS) Page Objects for URLs belonging to the domain toscrape.com. This must be done by configuring SCRAPY_POET_RULES into settings.py:

SCRAPY_POET_RULES = [
    ApplyRule("toscrape.com", BTSBookListPage, BookListPage),
    ApplyRule("toscrape.com", BTSBookPage, BookPage)
]

The spider is back to life! SCRAPY_POET_RULES contain rules that overrides the Page Objects used for a particular domain. In this particular case, Page Objects BTSBookListPage and BTSBookPage will be used instead of BookListPage and BookPage for any request whose domain is toscrape.com.

The right Page Objects will be then injected in the spider callbacks whenever a URL that belongs to the domain toscrape.com is requested.

Add another site

The code is now refactored to accept other implementations for other sites. Let’s illustrate it by adding support for the books in the page bookpage.com/reviews.

We cannot reuse the Books to Scrape Page Objects in this case. The site is different so their extraction logic wouldn’t work. Therefore, we have to implement new ones:

from web_poet.pages import WebPage


class BPBookListPage(WebPage):

    def book_urls(self):
        return self.css("article.post h4 a::attr(href)").getall()


class BPBookPage(WebPage):

    def to_item(self):
        return {
            "url": self.url,
            "name": self.css("body div > h1::text").get().strip(),
        }

The last step is configuring the overrides so that these new Page Objects are used for the domain bookpage.com. This is how SCRAPY_POET_RULES should look like into settings.py:

from web_poet import ApplyRule

SCRAPY_POET_RULES = [
    ApplyRule("toscrape.com", use=BTSBookListPage, instead_of=BookListPage),
    ApplyRule("toscrape.com", use=BTSBookPage, instead_of=BookPage),
    ApplyRule("bookpage.com", use=BPBookListPage, instead_of=BookListPage),
    ApplyRule("bookpage.com", use=BPBookPage, instead_of=BookPage)
]

The spider is now ready to extract books from both sites 😀. The full example can be seen here

On the surface, it looks just like a different way to organize Scrapy spider code - and indeed, it is just a different way to organize the code, but it opens some cool possibilities.

In the examples above we have been configuring the overrides for a particular domain, but more complex URL patterns are also possible. For example, the pattern books.toscrape.com/cataloge/category/ is accepted and it would restrict the override only to category pages.

Note

Also see the url-matcher documentation for more information about the patterns syntax.

Manually defining overrides like this would be inconvenient, most especially for larger projects. Fortunately, scrapy-poet already retrieves the rules defined from web-poet’s default_registry. This is done by setting the default value of the SCRAPY_POET_RULES setting as web_poet.default_registry.get_rules().

However, this only works if page objects are annotated using the web_poet.handle_urls() decorator. You also need to set the SCRAPY_POET_DISCOVER setting so that these rules could be properly imported.

For more info on this, you can refer to these docs:

• scrapy-poet’s Rules from web-poet Tutorial section.

• External web-poet docs.

  • Specifically, the Rules documentation.

Next steps

Now that you know how scrapy-poet is supposed to work, what about trying to apply it to an existing or new Scrapy project?

Also, please check the Rules from web-poet and Providers sections as well as refer to spiders in the “example” folder: https://github.com/scrapinghub/scrapy-poet/tree/master/example/example/spiders

Advanced Tutorial

This section intends to go over the supported features in web-poet by scrapy-poet:

• web_poet.HttpClient

• web_poet.PageParams

These are mainly achieved by scrapy-poet implementing providers for them:

• scrapy_poet.HttpClientProvider

• scrapy_poet.PageParamsProvider

Additional Requests

Using Page Objects using additional requests doesn’t need anything special from the spider. It would work as-is because of the readily available scrapy_poet.HttpClientProvider that is enabled out of the box.

This supplies the Page Object with the necessary web_poet.HttpClient instance.

The HTTP client implementation that scrapy-poet provides to web_poet.HttpClient handles requests as follows:

• Requests go through downloader middlewares, but they do not go through spider middlewares or through the scheduler.

• Duplicate requests are not filtered out.

• In line with the web-poet specification for additional requests, Request.meta["dont_redirect"] is set to True for requests with the HEAD HTTP method.

Suppose we have the following Page Object:

import attr
import web_poet


@attr.define
class ProductPage(web_poet.WebPage):
    http: web_poet.HttpClient

    async def to_item(self):
        item = {
            "url": self.url,
            "name": self.css("#main h3.name ::text").get(),
            "product_id": self.css("#product ::attr(product-id)").get(),
        }

        # Simulates clicking on a button that says "View All Images"
        response: web_poet.HttpResponse = await self.http.get(
            f"https://api.example.com/v2/images?id={item['product_id']}"
        )
        item["images"] = response.css(".product-images img::attr(src)").getall()
        return item

It can be directly used inside the spider as:

import scrapy


class ProductSpider(scrapy.Spider):

    custom_settings = {
        "DOWNLOADER_MIDDLEWARES": {
            "scrapy_poet.InjectionMiddleware": 543,
            "scrapy.downloadermiddlewares.stats.DownloaderStats": None,
            "scrapy_poet.DownloaderStatsMiddleware": 850,
        }
    }

    def start_requests(self):
        for url in [
            "https://example.com/category/product/item?id=123",
            "https://example.com/category/product/item?id=989",
        ]:
            yield scrapy.Request(url, callback=self.parse)

    async def parse(self, response, page: ProductPage):
        return await page.to_item()

Note that we needed to update the parse() method to be an async method, since the to_item() method of the Page Object we’re using is an async method as well.

Page params

Using web_poet.PageParams allows the Scrapy spider to pass any arbitrary information into the Page Object.

Suppose we update the earlier Page Object to control the additional request. This basically acts as a switch to update the behavior of the Page Object:

import attr
import web_poet


@attr.define
class ProductPage(web_poet.WebPage):
    http: web_poet.HttpClient
    page_params: web_poet.PageParams

    async def to_item(self):
        item = {
            "url": self.url,
            "name": self.css("#main h3.name ::text").get(),
            "product_id": self.css("#product ::attr(product-id)").get(),
        }

        # Simulates clicking on a button that says "View All Images"
        if self.page_params.get("enable_extracting_all_images")
            response: web_poet.HttpResponse = await self.http.get(
                f"https://api.example.com/v2/images?id={item['product_id']}"
            )
            item["images"] = response.css(".product-images img::attr(src)").getall()

        return item

Passing the enable_extracting_all_images page parameter from the spider into the Page Object can be achieved by using scrapy.Request.meta attribute. Specifically, any dict value inside the page_params parameter inside scrapy.Request.meta will be passed into web_poet.PageParams.

Let’s see it in action:

import scrapy


class ProductSpider(scrapy.Spider):

    custom_settings = {
        "DOWNLOADER_MIDDLEWARES": {
            "scrapy_poet.InjectionMiddleware": 543,
            "scrapy.downloadermiddlewares.stats.DownloaderStats": None,
            "scrapy_poet.DownloaderStatsMiddleware": 850,
        }
    }

    start_urls = [
        "https://example.com/category/product/item?id=123",
        "https://example.com/category/product/item?id=989",
    ]

    def start_requests(self):
        for url in start_urls:
            yield scrapy.Request(
                url=url,
                callback=self.parse,
                meta={"page_params": {"enable_extracting_all_images": True}}
            )

    async def parse(self, response, page: ProductPage):
        return await page.to_item()

Pitfalls

scrapy.Request without callback

Tip

Note that the pitfalls discussed in this section aren’t applicable to Scrapy >= 2.8 for most cases.

However, if you have code somewhere which directly adds scrapy.Request instances to the downloader, you need to ensure that they don’t use None as the callback value. Instead, you can use the new scrapy.http.request.NO_CALLBACK() value introduced in Scrapy 2.8.

Note

This section only applies to specific cases where spiders define a parse() method.

The TLDR; recommendation is to simply avoid defining a parse() method and instead choose another name.

Scrapy supports declaring scrapy.Request instances without setting any callbacks (i.e. None). For these instances, Scrapy uses the parse() method as its callback.

Let’s take a look at the following code:

import scrapy


class MySpider(scrapy.Spider):
    name = "my_spider"
    start_urls = ["https://books.toscrape.com"]

    def parse(self, response):
        ...

Under the hood, the inherited start_requests() method from scrapy.Spider doesn’t declare any callback value to scrapy.Request:

for url in self.start_urls:
    yield Request(url, dont_filter=True)

Apart from this, there are also some built-in Scrapy < 2.8 features which omit the scrapy.Request callback value:

• scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware

• scrapy.pipelines.images.ImagesPipeline

• scrapy.pipelines.files.FilesPipeline

However, omitting the scrapy.Request callback value presents some problems for scrapy-poet.

Skipped Downloads

Note

This subsection is specific to cases wherein a DummyResponse annotates the response in a parse() method.

Let’s take a look at an example:

import scrapy
from scrapy_poet import DummyResponse


class MySpider(scrapy.Spider):
    name = "my_spider"
    start_urls = ["https://books.toscrape.com"]

    def parse(self, response: DummyResponse):
        ...

In order for the built-in Scrapy < 2.8 features listed above to work properly, scrapy-poet chooses to ignore the DummyResponse annotation completely. This means that the response is downloaded instead of being skipped.

Otherwise, scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware might not work properly and would not visit the robots.txt file from the website.

Moreover, this scrapy-poet behavior avoids the problem of the images or files being missing when the following pipelines are used:

• scrapy.pipelines.images.ImagesPipeline

• scrapy.pipelines.files.FilesPipeline

Note that the following UserWarning is emitted when encountering such scenario:

A request has been encountered with callback=None which defaults to the parse() method. If the parse() method is annotated with scrapy_poet.DummyResponse (or its subclasses), we’re assuming this isn’t intended and would simply ignore this annotation.

To avoid the said warning and this scrapy-poet behavior from occurring, it’d be best to avoid defining a parse() method and instead choose any other name.

Dependency Building

Note

This subsection is specific to cases wherein dependencies are provided by scrapy-poet in the parse() method.

Let’s take a look at the following code:

import attrs
import scrapy

from myproject.page_objects import MyPage


class MySpider(scrapy.Spider):
    name = "my_spider"
    start_urls = ["https://books.toscrape.com"]

    def parse(self, response: scrapy.http.Response, page: MyPage):
        ...

In the above example, this error would be raised: TypeError: parse() missing 1 required positional argument: 'page'.

The reason for this scrapy-poet behavior is to prevent the wasted dependency building (which could be expensive in some cases) when the parse() method is unintentionally used.

For example, if a spider is using the scrapy.pipelines.images.ImagesPipeline, scrapy-poet’s scrapy_poet.downloadermiddlewares.InjectionMiddleware could be wasting precious compute resources to fulfill one or more dependencies that won’t be used at all. Specifically, the page argument to the parse() method is not utilized. If there are a million of images to be downloaded, then the page instance is created a million times as well.

The following UserWarning is emitted on such scenario:

A request has been encountered with callback=None which defaults to the parse() method. On such cases, annotated dependencies in the parse() method won’t be built by scrapy-poet. However, if the request has callback=parse, the annotated dependencies will be built.

As the warning message suggests, this could be fixed by ensuring that the callback is not None:

class MySpider(scrapy.Spider):
    name = "my_spider"

    def start_requests(self):
        yield scrapy.Request("https://books.toscrape.com", callback=self.parse)

    def parse(self, response: scrapy.http.Response, page: MyPage):
        ...

The UserWarning is only shown when the parse() method declares any dependency that is fullfilled by any provider declared in SCRAPY_POET_PROVIDERS. This means that the following code doesn’t produce the warning nor attempts to skip any dependency from being built because there is none:

class MySpider(scrapy.Spider):
    name = "my_spider"
    start_urls = ["https://books.toscrape.com"]

    def parse(self, response: scrapy.http.Response):
        ...

Similarly, the best way to completely avoid the said warning and this scrapy-poet behavior is to avoid defining a parse() method and instead choose any other name.

Opening a response in a web browser

When using scrapy-poet, the open_in_browser function from Scrapy may raise the following exception:

TypeError: Unsupported response type: HttpResponse

To avoid that, use the open_in_browser function from scrapy_poet.utils instead:

from scrapy_poet.utils import open_in_browser

Rules from web-poet

scrapy-poet fully supports the functionalities of web_poet.ApplyRule. It uses the registry from web_poet called web_poet.RulesRegistry which provides functionalties for:

• Returning the page object override if it exists for a given URL.

• Returning the page object capable of producing an item for a given URL.

A list of web_poet.ApplyRule can be configured by passing it to the SCRAPY_POET_RULES setting.

In this section, we go over its instead_of parameter for overrides and to_return for item returns. However, please make sure you also read web-poet’s Rules documentation to see all of the expected behaviors of the rules.

Overrides

This functionality opens the door to configure specific Page Objects depending on the request URL domain. Please have a look to Scrapy Tutorial to learn the basics about overrides before digging deeper in the content of this page.

Tip

Some real-world examples on this topic can be found in:

• Example 1: shorter example

• Example 2: longer example

• Example 3: rules using web_poet.handle_urls() decorator and retrieving them via web_poet.RulesRegistry.get_rules

Page Objects refinement

Any web_poet.pages.Injectable or page input can be overridden. But the overriding mechanism stops for the children of any already overridden type. This opens the door to refining existing Page Objects without getting trapped in a cyclic dependency. For example, you might have an existing Page Object for book extraction:

class BookPage(ItemPage):
    def to_item(self):
        ...

Imagine this Page Object obtains its data from an external API. Therefore, it is not holding the page HTML code. But you want to extract an additional attribute (e.g. ISBN) that was not extracted by the original Page Object. Using inheritance is not enough in this case, though. No problem, you can just override it using the following Page Object:

class ISBNBookPage(WebPage):

    def __init__(self, response: HttpResponse, book_page: BookPage):
        super().__init__(response)
        self.book_page = book_page

    def to_item(self):
        item = self.book_page.to_item()
        item['isbn'] = self.css(".isbn-class::text").get()
        return item

And then override it for a particular domain using settings.py:

SCRAPY_POET_RULES = [
    ApplyRule("example.com", use=ISBNBookPage, instead_of=BookPage)
]

This new Page Object gets the original BookPage as dependency and enrich the obtained item with the ISBN from the page HTML.

Note

By design overrides rules are not applied to ISBNBookPage dependencies as it is an overridden type. If they were, it would end up in a cyclic dependency error because ISBNBookPage would depend on itself!

Note

This is an alternative more compact way of writing the above Page Object using attr.define:

@attr.define
class ISBNBookPage(WebPage):
    book_page: BookPage

    def to_item(self):
        item = self.book_page.to_item()
        item['isbn'] = self.css(".isbn-class::text").get()
        return item

Overrides rules

The following example configures an override that is only applied for book pages from books.toscrape.com:

from web_poet import ApplyRule


SCRAPY_POET_RULES = [
    ApplyRule(
        for_patterns=Patterns(
            include=["books.toscrape.com/cataloge/*index.html|"],
            exclude=["/catalogue/category/"]),
        use=MyBookPage,
        instead_of=BookPage
    )
]

Note how category pages are excluded by using a exclude pattern. You can find more information about the patterns syntax in the url-matcher documentation.

Decorate Page Objects with the rules

Having the rules along with the Page Objects is a good idea, as you can identify with a single sight what the Page Object is doing along with where it is applied. This can be done by decorating the Page Objects with web_poet.handle_urls() provided by web-poet.

Tip

Make sure to read the Rules documentation of web-poet to learn all of its other functionalities that is not covered in this section.

Let’s see an example:

from web_poet import handle_urls


@handle_urls("toscrape.com", instead_of=BookPage)
class BTSBookPage(BookPage):

    def to_item(self):
        return {
            'url': self.url,
            'name': self.css("title::text").get(),
        }

The web_poet.handle_urls() decorator in this case is indicating that the class BSTBookPage should be used instead of BookPage for the domain toscrape.com.

Using the rules in scrapy-poet

scrapy-poet automatically uses the rules defined by page objects annotated with the web_poet.handle_urls() decorator by having the default value of the SCRAPY_POET_RULES setting set to web_poet.default_registry.get_rules(), which returns a List[ApplyRule]. Moreover, you also need to set the SCRAPY_POET_DISCOVER setting so that these rules could be properly imported.

Note

For more info and advanced features of web-poet’s web_poet.handle_urls() and its registry, kindly read the web-poet documentation, specifically its Rules documentation.

Item Returns

scrapy-poet also supports a convenient way of asking for items directly. This is made possible by the to_return parameter of web_poet.ApplyRule. The to_return parameter specifies which item a page object is capable of returning for a given URL.

Let’s check out an example:

import attrs
import scrapy
from web_poet import WebPage, handle_urls, field
from scrapy_poet import DummyResponse


@attrs.define
class Product:
    name: str


@handle_urls("example.com")
@attrs.define
class ProductPage(WebPage[Product]):

    @field
    def name(self) -> str:
        return self.css("h1.name ::text").get("")


class MySpider(scrapy.Spider):
    name = "myspider"

    def start_requests(self):
        yield scrapy.Request(
            "https://example.com/products/some-product", self.parse
        )

    # We can directly ask for the item here instead of the page object.
    def parse(self, response: DummyResponse, item: Product):
        return item

From this example, we can see that:

• Spider callbacks can directly ask for items as dependencies.

• The Product item instance directly comes from ProductPage.

• This is made possible by the ApplyRule("example.com", use=ProductPage, to_return=Product) instance created from the @handle_urls decorator on ProductPage.

Note

The slightly longer alternative way to do this is by declaring the page object itself as the dependency and then calling its .to_item() method. For example:

@handle_urls("example.com")
@attrs.define
class ProductPage(WebPage[Product]):
    product_image_page: ProductImagePage

    @field
    def name(self) -> str:
        return self.css("h1.name ::text").get("")

    @field
    async def image(self) -> Image:
        return await self.product_image_page.to_item()


class MySpider(scrapy.Spider):
    name = "myspider"

    def start_requests(self):
        yield scrapy.Request(
            "https://example.com/products/some-product", self.parse
        )

    async def parse(self, response: DummyResponse, product_page: ProductPage):
        return await product_page.to_item()

For more information about all the expected behavior for the to_return parameter in web_poet.ApplyRule, check out web-poet Rules documentation.

Stats

scrapy-poet tracks web-poet stats as part of Scrapy stats, prefixed with poet/stats/.

Injector stats

The injector produces some stats also. These are:

• cache stats have the poet/cache prefix.

• injected dependencies stats have the poet/injector prefix.

Providers

Note

This document assumes a good familiarity with web-poet concepts; make sure you’ve read web-poet docs.

This page is mostly aimed at developers who want to extend scrapy-poet, not to developers who are writing extraction and crawling code using scrapy-poet.

Creating providers

Providers are responsible for building dependencies needed by Injectable objects. A good example would be the scrapy_poet.HttpResponseProvider, which builds and provides a web_poet.HttpResponse instance for Injectables that need it, like the web_poet.WebPage.

import attr
from typing import Set, Callable

import web_poet
from scrapy_poet.page_input_providers import PageObjectInputProvider
from scrapy import Response


class HttpResponseProvider(PageObjectInputProvider):
    """This class provides ``web_poet.HttpResponse`` instances."""
    provided_classes = {web_poet.HttpResponse}

    def __call__(self, to_provide: Set[Callable], response: Response):
        """Build a ``web_poet.HttpResponse`` instance using a Scrapy ``Response``"""
        return [
            web_poet.HttpResponse(
                url=response.url,
                body=response.body,
                status=response.status,
                headers=web_poet.HttpResponseHeaders.from_bytes_dict(response.headers),
            )
        ]

You can implement your own providers in order to extend or override current scrapy-poet behavior. All providers should inherit from this base class: PageObjectInputProvider.

Please, check the docs provided in the following API reference for more details: PageObjectInputProvider.

Cache Support in Providers

scrapy-poet also supports caching of the provided dependencies from the providers. For example, HttpResponseProvider supports this right off the bat. It’s able to do this by inheriting the CacheDataProviderMixin and implementing all of its abstractmethods.

So, extending from the previous example we’ve tackled above to support cache would lead to the following code:

import web_poet
from scrapy_poet.page_input_providers import (
    CacheDataProviderMixin,
    PageObjectInputProvider,
)

class HttpResponseProvider(PageObjectInputProvider, CacheDataProviderMixin):
    """This class provides ``web_poet.HttpResponse`` instances."""
    provided_classes = {web_poet.HttpResponse}

    def __call__(self, to_provide: Set[Callable], response: Response):
        """Build a ``web_poet.HttpResponse`` instance using a Scrapy ``Response``"""
        return [
            web_poet.HttpResponse(
                url=response.url,
                body=response.body,
                status=response.status,
                headers=web_poet.HttpResponseHeaders.from_bytes_dict(response.headers),
            )
        ]

    def fingerprint(self, to_provide: Set[Callable], request: Request) -> str:
        """Returns a fingerprint to identify the specific request."""
        # Implementation here

    def serialize(self, result: Sequence[Any]) -> Any:
        """Serializes the results of this provider. The data returned will
        be pickled.
        """
        # Implementation here

    def deserialize(self, data: Any) -> Sequence[Any]:
        """Deserialize some results of the provider that were previously
        serialized using the serialize() method.
        """
        # Implementation here

Take note that even if you’re using providers that supports the Caching interface, it’s only going to be used if the SCRAPY_POET_CACHE has been enabled in the settings.

The caching of provided dependencies is very useful for local development of Page Objects, as it lowers down the waiting time for your Responses (or any type of external dependency for that manner) by caching them up locally.

Currently, the data is cached using a sqlite database in your local directory. This is implemented using SqlitedictCache.

The cache mechanism that scrapy-poet currently offers is quite different from the HttpCacheMiddleware which Scrapy has. Although they are quite similar in its intended purpose, scrapy-poet’s cached data is directly tied to its appropriate provider. This could be anything that could stretch beyond Scrapy’s Responses (e.g. Network Database queries, API Calls, AWS S3 files, etc).

Note

The scrapy_poet.injection.Injector maintains a .weak_cache which stores the instances created by the providers as long as the corresponding scrapy.Request instance exists. This means that the instances created by earlier providers can be accessed and reused by latter providers. This is turned on by default and the instances are stored in memory.

Configuring providers

The list of available providers should be configured in the spider settings. For example, the following configuration should be included in the settings to enable a new provider MyProvider:

"SCRAPY_POET_PROVIDERS": {MyProvider: 500}

The number used as value (500) defines the provider priority. See Scrapy Middlewares configuration dictionaries for more information.

Note

The providers in scrapy_poet.DEFAULT_PROVIDERS, which includes a provider for web_poet.HttpResponse, are always included by default. You can disable any of them by listing it in the configuration with the priority None.

Ignoring requests

Sometimes requests could be skipped, for example, when you’re fetching data using a third-party API such as Auto Extract or querying a database.

In cases like that, it makes no sense to send the request to Scrapy’s downloader as it will only waste network resources. But there’s an alternative to avoid making such requests, you could use DummyResponse type to annotate your response arguments.

That could be done in the spider’s parser method:

def parser(self, response: DummyResponse, page: MyPageObject):
    pass

Spider method that has its first argument annotated as DummyResponse is signaling that it is not going to use the response, so it should be safe to not download scrapy Response as usual.

This type annotation is already applied when you use the callback_for() helper: the callback which is created by callback_for doesn’t use Response, it just calls page object’s to_item method.

If neither spider callback nor any of the input providers are using Response, InjectionMiddleware skips the download, returning a DummyResponse instead. For example:

def get_cached_content(key: str):
    # get cached html response from db or other source
    pass


@attr.define
class CachedData:
    key: str
    value: str


class CachedDataProvider(PageObjectInputProvider):
    provided_classes = {CachedData}

    def __call__(self, to_provide: List[Callable], request: scrapy.Request):
        return [
            CachedData(
                key=request.url,
                value=get_cached_content(request.url)
            )
        ]


@attr.define
class MyPageObject(ItemPage):
    content: CachedData

    def to_item(self):
        return {
            "url": self.content.key,
            "content": self.content.value,
        }


class MySpider(scrapy.Spider):
    name = "my_spider"

    def start_requests(self):
        yield scrapy.Request("http://books.toscrape.com/", self.parse_page)

    def parse_page(self, response: DummyResponse, page: MyPageObject):
        # request will be IGNORED because neither spider callback
        # not MyPageObject seem like to be making use of its response
        yield page.to_item()

Although, if the spider callback is not using Response, but the Page Object uses it, the request is not ignored, for example:

def parse_content(html: str):
    # parse content from html
    pass


@attr.define
class MyResponseData:
    url: str
    html: str


class MyResponseDataProvider(PageObjectInputProvider):
    provided_classes = {MyResponseData}

    def __call__(self, to_provide: Set[Callable], response: Response):
        return [
            MyResponseData(
                url=response.url,
                html=response.content,
            )
        ]


class MyPageObject(ItemPage):
    response: MyResponseData

    def to_item(self):
        return {
            "url": self.response.url,
            "content": parse_content(self.response.html),
        }


class MySpider(scrapy.Spider):
    name = "my_spider"

    def start_requests(self):
        yield scrapy.Request("http://books.toscrape.com/", self.parse_page)

    def parse_page(self, response: DummyResponse, page: MyPageObject):
        # request will be PROCESSED because spider callback is not
        # making use of its response, but MyPageObject seems like to be
        yield page.to_item()

Note

The code above is just for example purposes. If you need to use scrapy.http.Response instances in your Page Objects, use built-in web_poet.WebPage — it has response attribute with web_poet.HttpResponse; no additional configuration is needed, as there is HttpResponseProvider enabled in scrapy-poet by default.

Requests concurrency

DummyRequests are meant to skip downloads, so it makes sense not checking for concurrent requests, delays, or auto throttle settings since we won’t be making any download at all.

By default, if your parser or its page inputs need a regular Request, this request is downloaded through Scrapy, and all the settings and limits are respected, for example:

• CONCURRENT_REQUESTS

• CONCURRENT_REQUESTS_PER_DOMAIN

• CONCURRENT_REQUESTS_PER_IP

• RANDOMIZE_DOWNLOAD_DELAY

• all AutoThrottle settings

• DownloaderAwarePriorityQueue logic

But be aware when using third-party libraries to acquire content for a page object. If you make an HTTP request in a provider using some third-party async library (aiohttp, treq, etc.), CONCURRENT_REQUESTS option will be respected, but not the others.

To have other settings respected, in addition to CONCURRENT_REQUESTS, you’d need to use crawler.engine.download or something like that. Alternatively, you could implement those limits in the library itself.

Attaching metadata to dependencies

Note

This feature requires Python 3.9+.

Providers can support dependencies with arbitrary metadata attached and use that metadata when creating them. Attaching the metadata is done by wrapping the dependency class in typing.Annotated:

@attr.define
class MyPageObject(ItemPage):
    response: Annotated[HtmlResponse, "foo", "bar"]

To handle this you need the following changes in your provider:

from andi.typeutils import strip_annotated
from scrapy_poet import PageObjectInputProvider
from web_poet.annotated import AnnotatedInstance


class Provider(PageObjectInputProvider):
    ...

    def is_provided(self, type_: Callable) -> bool:
        # needed so that you can list just the base type in provided_classes
        return super().is_provided(strip_annotated(type_))

    def __call__(self, to_provide):
        result = []
        for cls in to_provide:
            metadata = getattr(cls, "__metadata__", None)
            obj = ...  # create the instance using cls and metadata
            if metadata:
                # wrap the instance into a web_poet.annotated.AnnotatedInstance object
                obj = AnnotatedInstance(obj, metadata)
            result.append(obj)
        return result

Tests for Page Objects

web-poet provides tools for testing page objects. scrapy-poet projects can use a Scrapy command to easily generate tests:

scrapy savefixture my_project.pages.MyItemPage 'https://quotes.toscrape.com/page/1/'

This will request the provided page, create an instance of the provided page object for this page, request its to_item() method and save both the page object dependencies and the resulting item as a test fixture. These fixtures can then be used with the pytest plugin provided by web-poet.

Configuring the test location

The SCRAPY_POET_TESTS_DIR setting specifies where to create the tests. It can be set in the project settings or with the -s command argument.

Handling time fields

The tests generated by savefixture set the frozen_time metadata value to the time of the test creation.

Using spiders

By default savefixture creates a simple spider that uses the project settings and makes one request to the URL provided to the command. It may be needed instead to use a real spider from the project, for example because of its custom_settings. In this case you can pass the spider name as the third argument:

scrapy savefixture my_project.pages.MyItemPage 'https://quotes.toscrape.com/page/1/' toscrape_listing

The command will try to run the spider overriding its start_requests(), so it should run just one request but it can break on spiders with complicated logic, e.g. ones that use spider_idle to schedule requests or modify items returned from to_item(). You may need to adapt your spiders to this, for example checking if the special _SCRAPY_POET_SAVEFIXTURE setting is set to True and using more simple logic in this case.

Configuring the item adapter

As documented in Item adapters, fixtures can use custom item adapters. The savefixture command uses the adapter specified in the SCRAPY_POET_TESTS_ADAPTER setting to save the fixture.

Settings

Configuring the settings denoted below would follow the usual methods used by Scrapy.

SCRAPY_POET_PROVIDERS

Default: {}

A dict wherein the keys would be the providers available for your Scrapy project while the values denotes the priority of the provider.

More info on this at this section: Providers.

SCRAPY_POET_OVERRIDES

Deprecated. Use SCRAPY_POET_RULES instead.

SCRAPY_POET_RULES

Default: web_poet.default_registry.get_rules()

Accepts a List[ApplyRule] which sets the rules to use.

Warning

Although SCRAPY_POET_RULES already has values set from the return value of web_poet.default_registry.get_rules(), make sure to also set the SCRAPY_POET_DISCOVER setting below.

There are sections dedicated for this at Scrapy Tutorial and Rules from web-poet.

SCRAPY_POET_DISCOVER

Default: []

A list of packages/modules (i.e. List[str]) which scrapy-poet will look for page objects annotated with the web_poet.handle_urls() decorator. Each package/module is passed into web_poet.consume_modules where each module from a package is recursively loaded.

This ensures that when using the default value of SCRAPY_POET_RULES set to web_poet.default_registry.get_rules(), it should contain all the intended rules.

Note that it’s also possible for SCRAPY_POET_RULES to have rules not specified in SCRAPY_POET_DISCOVER (e.g. when the annotated page objects are inside your Scrapy project). However, it’s recommended to still use SCRAPY_POET_DISCOVER to ensure all the intended rules are properly loaded.

SCRAPY_POET_CACHE

Default: None

The caching mechanism in the providers can be enabled by either setting this to True which configures the file path of the cache into a .scrapy/ dir in your local Scrapy project.

On the other hand, you can also set this as a str pointing to any path relative to your local Scrapy project.

SCRAPY_POET_CACHE_ERRORS

Default: False

When this is set to True, any error that arises when retrieving dependencies from providers would be cached. This could be useful in cases during local development wherein you outright know that retrieving the dependency would fail and would choose to ignore it. Caching such errors would reduce the waiting time when developing Page Objects.

It’s recommended to set this off into False by default since you might miss out on sporadic errors.

SCRAPY_POET_TESTS_DIR

Default: fixtures

Sets the location where the savefixture command creates tests.

More info at Tests for Page Objects.

SCRAPY_POET_TESTS_ADAPTER

Default: None

Sets the class, or its import path, that will be used as an adapter in the generated test fixtures.

More info at Configuring the item adapter.

SCRAPY_POET_REQUEST_FINGERPRINTER_BASE_CLASS

The default value is the default value of the REQUEST_FINGERPRINTER_CLASS setting for the version of Scrapy currently installed (e.g. "scrapy.utils.request.RequestFingerprinter").

You can assign a request fingerprinter class to this setting to configure a custom request fingerprinter class to use for requests.

This class is used to generate a base fingerprint for a request. If that request uses dependency injection, that fingerprint is then modified to account for requested dependencies. Otherwise, the fingerprint is used as is.

Note

Annotations of annotated dependencies are serialized with repr() for fingerprinting purposes. If you find a real-world scenario where this is a problem, please open an issue.

API Reference

API

scrapy_poet.callback_for(page_or_item_cls: Type) → Callable

Create a callback for an web_poet.ItemPage subclass or an item class.

The generated callback returns the output of the to_item method, i.e. extracts a single item from a web page, using a Page Object.

This helper allows to reduce the boilerplate when working with Page Objects. For example, instead of this:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    def parse_book(self, response: DummyResponse, page: BookPage):
        return page.to_item()

It allows to write this:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    parse_book = callback_for(BookPage)

It also supports producing an async generator callable if the Page Objects’s to_item method is a coroutine which uses the async/await syntax.

So if we have the following:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    async def parse_book(self, response: DummyResponse, page: BookPage):
        yield await page.to_item()

It could be turned into:

class BooksSpider(scrapy.Spider):
    name = "books"
    start_urls = ["http://books.toscrape.com/"]

    def parse(self, response):
        links = response.css(".image_container a")
        yield from response.follow_all(links, self.parse_book)

    parse_book = callback_for(BookPage)

The generated callback could be used as a spider instance method or passed as an inline/anonymous argument. Make sure to define it as a spider attribute (as shown in the example above) if you’re planning to use disk queues, because in this case Scrapy is able to serialize your request object.

class scrapy_poet.DummyResponse(*args: Any, **kwargs: Any)

This class is returned by the InjectionMiddleware when it detects that the download could be skipped. It inherits from scrapy.http.Response and signals and stores the URL and references the original scrapy.Request.

If you want to skip downloads, you can type annotate your parse method with this class.

def parse(self, response: DummyResponse):
    pass

If there’s no Page Input that depends on a scrapy.http.Response, the InjectionMiddleware is going to skip download and provide a DummyResponse to your parser instead.

Injection Middleware

An important part of scrapy-poet is the Injection Middleware. It’s responsible for injecting Page Input dependencies before the request callbacks are executed.

class scrapy_poet.downloadermiddlewares.InjectionMiddleware(crawler: Crawler)

This is a Downloader Middleware that’s supposed to:

• check if request downloads could be skipped

• inject dependencies before request callbacks are executed

__init__(crawler: Crawler) → None

Initialize the middleware

process_request(request: Request, spider: Spider) → DummyResponse | None

This method checks if the request is really needed and if its download could be skipped by trying to infer if a scrapy.http.Response is going to be used by the callback or a Page Input.

If the scrapy.http.Response can be ignored, a DummyResponse instance is returned on its place. This DummyResponse is linked to the original scrapy.Request instance.

With this behavior, we’re able to optimize spider executions avoiding unnecessary downloads. That could be the case when the callback is actually using another source like external APIs such as Zyte’s AutoExtract.

process_response(request: Request, response: Response, spider: Spider) → Generator[Deferred, object, Response]

This method fills scrapy.Request.cb_kwargs with instances for the required Page Objects found in the callback signature.

In other words, this method instantiates all web_poet.Injectable subclasses declared as request callback arguments and any other parameter with a PageObjectInputProvider configured for its type.

Page Input Providers

The Injection Middleware needs a standard way to build the Page Inputs dependencies that the Page Objects uses to get external data (e.g. the HTML). That’s why we have created a colletion of Page Object Input Providers.

The current module implements a Page Input Provider for web_poet.HttpResponse, which is in charge of providing the response HTML from Scrapy. You could also implement different providers in order to acquire data from multiple external sources, for example, from scrapy-playwright or from an API for automatic extraction.

class scrapy_poet.page_input_providers.HttpClientProvider(injector)

This class provides web_poet.HttpClient instances.

__call__(to_provide: Set[Callable], crawler: Crawler)

Creates an web_poet.HttpClient instance using Scrapy’s downloader.

class scrapy_poet.page_input_providers.HttpRequestProvider(injector)

This class provides web_poet.HttpRequest instances.

__call__(to_provide: Set[Callable], request: Request)

Builds a web_poet.HttpRequest instance using a scrapy.http.Request instance.

class scrapy_poet.page_input_providers.HttpResponseProvider(injector)

This class provides web_poet.HttpResponse instances.

__call__(to_provide: Set[Callable], response: Response)

Builds a web_poet.HttpResponse instance using a scrapy.http.Response instance.

class scrapy_poet.page_input_providers.ItemProvider(injector)

async __call__(to_provide: Set[Callable], request: Request, response: Response) → List[Any]

Call self as a function.

__init__(injector)

Initializes the provider. Invoked only at spider start up.

class scrapy_poet.page_input_providers.PageObjectInputProvider(injector)

This is the base class for creating Page Object Input Providers.

A Page Object Input Provider (POIP) takes responsibility for providing instances of some types to Scrapy callbacks. The types a POIP provides must be declared in the class attribute provided_classes.

POIPs are initialized when the spider starts by invoking the __init__ method, which receives the scrapy_poet.injection.Injector instance as argument.

The __call__ method must be overridden, and it is inside this method where the actual instances must be build. The default __call__ signature is as follows:

def __call__(self, to_provide: Set[Callable]) -> Sequence[Any]:

Therefore, it receives a list of types to be provided and return a list with the instances created (don’t get confused by the Callable annotation. Think on it as a synonym of Type).

Additional dependencies can be declared in the __call__ signature that will be automatically injected. Currently, scrapy-poet is able to inject instances of the following classes:

• Request

• Response

• Crawler

• Settings

• StatsCollector

Finally, __call__ function can execute asynchronous code. Just either prepend the declaration with async to use futures or annotate it with @inlineCallbacks for deferred execution. Additionally, you might want to configure Scrapy TWISTED_REACTOR to support asyncio libraries.

The available POIPs should be declared in the spider setting using the key SCRAPY_POET_PROVIDERS. It must be a dictionary that follows same structure than the Scrapy Middlewares configuration dictionaries.

A simple example of a provider:

class BodyHtml(str): pass

class BodyHtmlProvider(PageObjectInputProvider):
    provided_classes = {BodyHtml}

    def __call__(self, to_provide, response: Response):
        return [BodyHtml(response.css("html body").get())]

The provided_classes class attribute is the set of classes that this provider provides. Alternatively, it can be a function with type Callable[[Callable], bool] that returns True if and only if the given type, which must be callable, is provided by this provider.

__init__(injector)

Initializes the provider. Invoked only at spider start up.

is_provided(type_: Callable) → bool

Return True if the given type is provided by this provider based on the value of the attribute provided_classes

class scrapy_poet.page_input_providers.PageParamsProvider(injector)

This class provides web_poet.PageParams instances.

__call__(to_provide: Set[Callable], request: Request)

Creates a web_poet.PageParams instance based on the data found from the meta["page_params"] field of a scrapy.http.Response instance.

class scrapy_poet.page_input_providers.RequestUrlProvider(injector)

This class provides web_poet.RequestUrl instances.

__call__(to_provide: Set[Callable], request: Request)

Builds a web_poet.RequestUrl instance using scrapy.Request instance.

class scrapy_poet.page_input_providers.ResponseUrlProvider(injector)

__call__(to_provide: Set[Callable], response: Response)

Builds a web_poet.RequestUrl instance using a scrapy.http.Response instance.

class scrapy_poet.page_input_providers.ScrapyPoetStatCollector(stats)

__init__(stats)

inc(key: str, value: int | float = 1) → None

Increment the value of stat key by value, or set it to value if key has no value.

set(key: str, value: Any) → None

Set the value of stat key to value.

class scrapy_poet.page_input_providers.StatsProvider(injector)

This class provides web_poet.Stats instances.

__call__(to_provide: Set[Callable], crawler: Crawler)

Creates an web_poet.Stats instance using Scrapy’s stat collector.

Cache

class scrapy_poet.cache.SerializedDataCache(directory: str | PathLike)

Stores dependencies from Providers in a persistent local storage using web_poet.serialization.SerializedDataFileStorage

__init__(directory: str | PathLike) → None

Injection

class scrapy_poet.injection.Injector(crawler: Crawler, *, default_providers: Mapping | None = None, registry: RulesRegistry | None = None)

Keep all the logic required to do dependency injection in Scrapy callbacks. Initializes the providers from the spider settings at initialization.

__init__(crawler: Crawler, *, default_providers: Mapping | None = None, registry: RulesRegistry | None = None)

build_callback_dependencies(request: Request, response: Response)

Scan the configured callback for this request looking for the dependencies and build the corresponding instances. Return a kwargs dictionary with the built instances.

build_instances(request: Request, response: Response, plan: Plan)

Build the instances dict from a plan including external dependencies.

build_instances_from_providers(request: Request, response: Response, plan: Plan)

Build dependencies handled by registered providers

build_plan(request: Request) → Plan

Create a plan for building the dependencies required by the callback

discover_callback_providers(request: Request) → Set[PageObjectInputProvider]

Discover the providers that are required to fulfil the callback dependencies

is_scrapy_response_required(request: Request)

Check whether Scrapy’s Request’s Response is going to be used.

scrapy_poet.injection.get_callback(request, spider)

Get the scrapy.Request.callback of a scrapy.Request.

scrapy_poet.injection.get_injector_for_testing(providers: Mapping, additional_settings: Dict | None = None, registry: RulesRegistry | None = None) → Injector

Return an Injector using a fake crawler. Useful for testing providers

scrapy_poet.injection.get_response_for_testing(callback: Callable) → Response

Return a scrapy.http.Response with fake content with the configured callback. It is useful for testing providers.

scrapy_poet.injection.is_callback_requiring_scrapy_response(callback: ~typing.Callable, raw_callback: ~typing.Any = <object object>) → bool

Check whether the request’s callback method requires the response. Basically, it won’t be required if the response argument in the callback is annotated with DummyResponse.

scrapy_poet.injection.is_class_provided_by_any_provider_fn(providers: List[PageObjectInputProvider]) → Callable[[Callable], bool]

Return a function of type Callable[[Type], bool] that return True if the given type is provided by any of the registered providers.

The is_provided method from each provider is used.

scrapy_poet.injection.is_provider_requiring_scrapy_response(provider)

Check whether injectable provider makes use of a valid scrapy.http.Response.

Injection errors

exception scrapy_poet.injection_errors.InjectionError

exception scrapy_poet.injection_errors.MalformedProvidedClassesError

exception scrapy_poet.injection_errors.NonCallableProviderError

exception scrapy_poet.injection_errors.ProviderDependencyDeadlockError

This is raised when it’s not possible to create the dependencies due to deadlock.

For example:

• Page object named “ChickenPage” require “EggPage” as a dependency.

• Page object named “EggPage” require “ChickenPage” as a dependency.

exception scrapy_poet.injection_errors.UndeclaredProvidedTypeError

Contributing

scrapy-poet is an open-source project. Your contribution is very welcome!

Issue Tracker

If you have a bug report, a new feature proposal or simply would like to make a question, please check our issue tracker on Github: https://github.com/scrapinghub/scrapy-poet/issues

Source code

Our source code is hosted on Github: https://github.com/scrapinghub/scrapy-poet

Before opening a pull request, it might be worth checking current and previous issues. Some code changes might also require some discussion before being accepted so it might be worth opening a new issue before implementing huge or breaking changes.

Testing

We use tox to run tests with different Python versions:

tox

The command above also runs type checks; we use mypy.

Changelog

0.22.3 (2024-04-25)

• scrapy_poet.utils.testing.make_crawler() now respects setting priorities when it receives a Settings object instead of a dict.

0.22.2 (2024-04-24)

• HttpRequestProvider, added in 0.17.0, is now actually enabled by default.

0.22.1 (2024-03-07)

• Fixed scrapy savefixture not finding page object modules when used outside a Scrapy project.

0.22.0 (2024-03-04)

• Now requires web-poet >= 0.17.0 and time_machine >= 2.7.1.

• Removed scrapy_poet.AnnotatedResult, use web_poet.annotated.AnnotatedInstance instead.

• Added support for annotated dependencies to the scrapy savefixture command.

• Test improvements.

0.21.0 (2024-02-08)

• Added a .weak_cache to scrapy_poet.injection.Injector which stores instances created by providers as long as the scrapy.Request exists.

• Fixed the incorrect value of downloader/response_count in the stats due to additional counting of scrapy_poet.api.DummyResponse.

• Fixed the detection of scrapy_poet.api.DummyResponse when some type hints are annotated using strings.

0.20.1 (2024-01-24)

• ScrapyPoetRequestFingerprinter now supports item dependencies.

0.20.0 (2024-01-15)

• Add ScrapyPoetRequestFingerprinter, a request fingerprinter that uses request dependencies in the fingerprint generation.

0.19.0 (2023-12-26)

• Now requires andi >= 0.6.0.

• Changed the implementation of resolving and building item dependencies from page objects. Now andi custom builders are used to create a single plan that includes building page objects and items. This fixes problems such as providers being called multiple times.

  • ItemProvider is now no-op. It’s no longer enabled by default and users should also stop enabling it.

  • PageObjectInputProvider.allow_prev_instances and code related to it were removed so custom providers may need updating.

• Fixed some tests.

0.18.0 (2023-12-12)

• Now requires andi >= 0.5.0.

• Add support for dependency metadata via typing.Annotated (requires Python 3.9+).

0.17.0 (2023-12-11)

• Now requires web-poet >= 0.15.1.

• HttpRequest dependencies are now supported, via HttpRequestProvider (enabled by default).

• Enable StatsProvider, which provides Stats dependencies, by default.

• More robust disabling of InjectionMiddleware in the scrapy savefixture command.

• Official support for Python 3.12.

0.16.1 (2023-11-02)

• Fix the bug that caused requests produced by HttpClientProvider to be treated as if they need arguments of the parse callback as dependencies, which could cause returning an empty response and/or making extra provider calls.

0.16.0 (2023-09-26)

• Now requires time_machine >= 2.2.0.

• ItemProvider now supports page objects that declare a dependency on the same type of item that they return, as long as there is an earlier page object input provider that can provide such dependency.

• Fix running tests with Scrapy 2.11.

0.15.1 (2023-09-15)

• scrapy-poet stats now also include counters for injected dependencies (poet/injector/<dependency import path>).

• All scrapy-poet stats that used to be prefixed with scrapy-poet/ are now prefixed with poet/ instead.

0.15.0 (2023-09-12)

• Now requires web-poet >= 0.15.0.

• Web-poet stats are now supported.

0.14.0 (2023-09-08)

• Python 3.7 support has been dropped.

• Caching is now built on top of web-poet serialization, extending caching support to additional inputs, while making our code simpler, more reliable, and more future-proof.

  This has resulted in a few backward-incompatible changes:

  • The scrapy_poet.page_input_providers.CacheDataProviderMixin mixin class has been removed. Providers no longer need to use it or reimplement its methods.

  • The SCRAPY_POET_CACHE_GZIP setting has been removed.

• Added scrapy_poet.utils.open_in_browser, an alternative to scrapy.utils.response.open_in_browser that supports scrapy-poet.

• Fixed some documentation links.

0.13.0 (2023-05-08)

• Now requires web-poet >= 0.12.0.

• The scrapy savefixture command now uses the adapter from the SCRAPY_POET_TESTS_ADAPTER setting to save the fixture.

• Fix a typo in the docs.

0.12.0 (2023-04-26)

• Now requires web-poet >= 0.11.0.

• The scrapy savefixture command can now generate tests that expect that to_item() raises a specific exception (only web_poet.exceptions.PageObjectAction and its descendants are expected).

• Fixed an error when using scrapy shell with scrapy_poet.InjectionMiddleware enabled.

• Add a twine check CI check.

0.11.0 (2023-03-17)

• The scrapy savefixture command can now generate a fixture using an existing spider.

0.10.1 (2023-03-03)

• More robust time freezing in scrapy savefixture command.

0.10.0 (2023-02-24)

• Now requires web-poet >= 0.8.0.

• The savefixture command now also saves requests made via the web_poet.page_inputs.client.HttpClient dependency and their responses.

0.9.0 (2023-02-17)

• Added support for item classes which are used as dependencies in page objects and spider callbacks. The following is now possible:

  import attrs
  import scrapy
  from web_poet import WebPage, handle_urls, field
  from scrapy_poet import DummyResponse
  
  @attrs.define
  class Image:
      url: str
  
  @handle_urls("example.com")
  class ProductImagePage(WebPage[Image]):
      @field
      def url(self) -> str:
          return self.css("#product img ::attr(href)").get("")
  
  @attrs.define
  class Product:
      name: str
      image: Image
  
  @handle_urls("example.com")
  @attrs.define
  class ProductPage(WebPage[Product]):
      # ✨ NEW: The page object can ask for items as dependencies. An instance
      # of ``Image`` is injected behind the scenes by calling the ``.to_item()``
      # method of ``ProductImagePage``.
      image_item: Image
  
      @field
      def name(self) -> str:
          return self.css("h1.name ::text").get("")
  
      @field
      def image(self) -> Image:
          return self.image_item
  
  class MySpider(scrapy.Spider):
      name = "myspider"
  
      def start_requests(self):
          yield scrapy.Request(
              "https://example.com/products/some-product", self.parse_product
          )
  
      # ✨ NEW: We can directly use the item here instead of the page object.
      def parse_product(self, response: DummyResponse, item: Product) -> Product:
          return item
  

  In line with this, the following new features were made:

  • New scrapy_poet.page_input_providers.ItemProvider which makes the usage above possible.

  • An item class is now supported by scrapy_poet.callback_for() alongside the usual page objects. This means that it won’t raise a TypeError anymore when not passing a subclass of web_poet.pages.ItemPage.

  • New exception: scrapy_poet.injection_errors.ProviderDependencyDeadlockError. This is raised when it’s not possible to create the dependencies due to a deadlock in their sub-dependencies, e.g. due to a circular dependency between page objects.

• New setting named SCRAPY_POET_RULES having a default value of web_poet.default_registry.get_rules. This deprecates SCRAPY_POET_OVERRIDES.

• New setting named SCRAPY_POET_DISCOVER to ensure that SCRAPY_POET_RULES have properly loaded all intended rules annotated with the @handle_urls decorator.

• New utility functions in scrapy_poet.utils.testing.

• The frozen_time value inside the test fixtures won’t contain microseconds anymore.

• Supports the new scrapy.http.request.NO_CALLBACK() introduced in Scrapy 2.8. This means that the Pitfalls (introduced in scrapy-poet==0.7.0) doesn’t apply when you’re using Scrapy >= 2.8, unless you’re using third-party middlewares which directly uses the downloader to add scrapy.Request instances with callback set to None. Otherwise, you need to set the callback value to scrapy.http.request.NO_CALLBACK().

• Fix the TypeError that’s raised when using Twisted <= 21.7.0 since scrapy-poet was using twisted.internet.defer.Deferred[object] type annotation before which was not subscriptable in the early Twisted versions.

• Fix the twisted.internet.error.ReactorAlreadyInstalledError error raised when using the scrapy savefixture command and Twisted < 21.2.0 is installed.

• Fix test configuration that doesn’t follow the intended commands and dependencies in these tox environments: min, asyncio-min, and asyncio. This ensures that page objects using asyncio should work properly, alongside the minimum specified Twisted version.

• Various improvements to tests and documentation.

• Backward incompatible changes:

  • For the scrapy_poet.page_input_providers.PageObjectInputProvider base class:

    • It now accepts an instance of scrapy_poet.injection.Injector in its constructor instead of scrapy.crawler.Crawler. Although you can still access the scrapy.crawler.Crawler via the Injector.crawler attribute.

    • scrapy_poet.page_input_providers.PageObjectInputProvider.is_provided() is now an instance method instead of a class method.

  • The scrapy_poet.injection.Injector’s attribute and constructor parameter called overrides_registry is now simply called registry.

  • Removed the SCRAPY_POET_OVERRIDES_REGISTRY setting which overrides the default registry.

  • The scrapy_poet.overrides module which contained OverridesRegistryBase and OverridesRegistry has now been removed. Instead, scrapy-poet directly uses web_poet.rules.RulesRegistry.

    Everything should pretty much the same except for web_poet.rules.RulesRegistry.overrides_for() now accepts str, web_poet.page_inputs.http.RequestUrl, or web_poet.page_inputs.http.ResponseUrl instead of scrapy.http.Request.

  • This also means that the registry doesn’t accept tuples as rules anymore. Only web_poet.rules.ApplyRule instances are allowed. The same goes for SCRAPY_POET_RULES (and the deprecated SCRAPY_POET_OVERRIDES).

  • The following type aliases have been removed:

    • scrapy_poet.overrides.RuleAsTuple

    • scrapy_poet.overrides.RuleFromUser

0.8.0 (2023-01-24)

• Now requires web-poet >= 0.7.0 and time_machine.

• Added a savefixture command that creates a test for a page object. See Tests for Page Objects for more information.

0.7.0 (2023-01-17)

• Fixed the issue where a new page object containing a new response data is not properly created when web_poet.exceptions.core.Retry is raised.

• In order for the above fix to be possible, overriding the callback dependencies created by scrapy-poet via scrapy.http.Request.cb_kwargs is now unsupported. This is a backward incompatible change.

• Fixed the broken scrapy_poet.page_input_providers.HttpResponseProvider.fingerprint() which errors out when running a Scrapy job using the SCRAPY_POET_CACHE enabled.

• Improved behavior when spider.parse() method arguments are supposed to be provided by scrapy-poet. Previously, it was causing unnecessary work in unexpected places like scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware, scrapy.pipelines.images.ImagesPipeline or scrapy.pipelines.files.FilesPipeline. It is also a reason web_poet.page_inputs.client.HttpClient might not be working in page objects. Now these cases are detected, and a warning is issued.

  As of Scrapy 2.7, it is not possible to fix the issue completely in scrapy-poet. Fixing it would require Scrapy changes; some 3rd party libraries may also need to be updated.

  Note

  The root of the issue is that when request.callback is None, parse() callback is assumed normally. But sometimes callback=None is used when scrapy.http.Request is added to the Scrapy’s downloader directly, in which case no callback is used. Middlewares, including scrapy-poet’s, can’t distinguish between these two cases, which causes all kinds of issues.

  We recommend all scrapy-poet users to modify their code to avoid the issue. Please don’t define parse() method with arguments which are supposed to be filled by scrapy-poet, and rename the existing parse() methods if they have such arguments. Any other name is fine. It avoids all possible issues, including incompatibility with 3rd party middlewares or pipelines.

  See the new Pitfalls documentation for more information.

  There are backwards-incompatible changes related to this issue. They only affect you if you don’t follow the advice of not using parse() method with scrapy-poet.

  • When the parse() method has its response argument annotated with scrapy_poet.api.DummyResponse, for instance: def parse(self, response: DummyResponse), the response is downloaded instead of being skipped.

  • When the parse() method has dependencies that are provided by scrapy-poet, the scrapy_poet.downloadermiddlewares.InjectionMiddleware won’t attempt to build any dependencies anymore.

    This causes the following code to have this error TypeError: parse() missing 1 required positional argument: 'page'.:

    class MySpider(scrapy.Spider):
        name = "my_spider"
        start_urls = ["https://books.toscrape.com"]
    
        def parse(self, response: scrapy.http.Response, page: MyPage):
            ...
    

• scrapy_poet.injection.is_callback_requiring_scrapy_response() now accepts an optional raw_callback parameter meant to represent the actual callback attribute value of scrapy.http.Request since the original callback parameter could be normalized to the spider’s parse() method when the scrapy.http.Request has callback set to None.

• Official support for Python 3.11

• Various updates and improvements on docs and examples.

0.6.0 (2022-11-24)

• Now requires web-poet >= 0.6.0.

  • All examples in the docs and tests now use web_poet.WebPage instead of web_poet.ItemWebPage.

  • The new instead_of parameter of the @handle_urls decorator is now preferred instead of the deprecated overrides parameter.

  • scrapy_poet.callback_for doesn’t require an implemented to_item method anymore.

  • The new web_poet.rules.RulesRegistry is used instead of the old web_poet.overrides.PageObjectRegistry.

  • The Registry now uses web_poet.ApplyRule instead of web_poet.OverrideRule.

• Provider for web_poet.ResponseUrl is added, which allows to access the response URL in the page object. This triggers a download unlike the provider for web_poet.RequestUrl.

• Fixes the error when using scrapy shell while the scrapy_poet.InjectionMiddleware is enabled.

• Fixes and improvements on code and docs.

0.5.1 (2022-07-28)

Fixes the minimum web-poet version being 0.5.0 instead of 0.4.0.

0.5.0 (2022-07-28)

This release implements support for page object retries, introduced in web-poet 0.4.0.

To enable retry support, you need to configure a new spider middleware in your Scrapy settings:

SPIDER_MIDDLEWARES = {
    "scrapy_poet.RetryMiddleware": 275,
}

web-poet 0.4.0 is now the minimum required version of web-poet.

0.4.0 (2022-06-20)

This release is backwards incompatible, following backwards-incompatible changes in web-poet 0.2.0.

The main new feature is support for web-poet >= 0.2.0, including support for async def to_item methods, making additional requests in the to_item method, new Page Object dependencies, and the new way to configure overrides.

Changes in line with web-poet >= 0.2.0:

• web_poet.HttpResponse replaces web_poet.ResponseData as a dependency to use.

• Additional requests inside Page Objects: a provider for web_poet.HttpClient, as well as web_poet.HttpClient backend implementation, which uses Scrapy downloader.

• callback_for now supports Page Objects which define async def to_item method.

• Provider for web_poet.PageParams is added, which uses request.meta["page_params"] value.

• Provider for web_poet.RequestUrl is added, which allows to access the request URL in the page object without triggering the download.

• We have these backward incompatible changes since the web_poet.OverrideRule follow a different structure:

  • Deprecated PerDomainOverridesRegistry in lieu of the newer OverridesRegistry which provides a wide variety of features for better URL matching.

  • This resuls in a newer format in the SCRAPY_POET_OVERRIDES setting.

Other changes:

• New scrapy_poet/dummy_response_count value appears in Scrapy stats; it is the number of times DummyResponse is used instead of downloading the response as usual.

• scrapy.utils.reqser deprecated module is no longer used by scrapy-poet.

Dependency updates:

• The minimum supported Scrapy version is now 2.6.0.

• The minimum supported web-poet version is now 0.2.0.

0.3.0 (2022-01-28)

• Cache mechanism using SCRAPY_POET_CACHE

• Fixed and improved docs

• removed support for Python 3.6

• added support for Python 3.10

0.2.1 (2021-06-11)

• Improved logging message for DummyResponse

• various internal cleanups

0.2.0 (2021-01-22)

• Overrides support

0.1.0 (2020-12-29)

• New providers interface

  • One provider can provide many types at once

  • Single instance during the whole spider lifespan

  • Registration is now explicit and done in the spider settings

• CI is migrated from Travis to Github Actions

• Python 3.9 support

0.0.3 (2020-07-19)

• Documentation improvements

• providers can now access various Scrapy objects: Crawler, Settings, Spider, Request, Response, StatsCollector

0.0.2 (2020-04-28)

The repository is renamed to scrapy-poet, and split into two:

• web-poet (https://github.com/scrapinghub/web-poet) contains definitions and code useful for writing Page Objects for web data extraction - it is not tied to Scrapy;

• scrapy-poet (this package) provides Scrapy integration for such Page Objects.

API of the library changed in a backwards incompatible way; see README and examples.

New features:

• DummyResponse annotation allows to skip downloading of scrapy Response.

• callback_for works for Scrapy disk queues if it is used to create a spider method (but not in its inline form)

• Page objects may require page objects as dependencies; dependencies are resolved recursively and built as needed.

• InjectionMiddleware supports async def and asyncio providers.

0.0.1 (2019-08-28)

Initial release.

License

Copyright (c) Scrapinghub All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of ScrapingHub nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.