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Spider Control

ruia.Spider is used to control the whole spider, it provides the following functions:

  • Normalize your code
  • Maintain a event loop
  • Manage requests and responses
  • Concurrency control
  • Manage middlewares and plugins

Although it works well, to use only ruia.Item to create a spider, ruia recommend to use ruia.Spider to implement a stronger spider.

Normalize your code

ruia.Spider requires a class property start_urls as the entry point of a spider. Inner, ruia will iterate start_urls, and send a request to server for each request. After receiving server response, ruia will call spider.parse(response), and this is the main part of your spider.

Here's a simple parse example, to simply save response fields to a text file. We only have to define start_urls, and implement a parse method.

import aiofiles

from ruia import Spider, Item, TextField, AttrField


class HackerNewsItem(Item):
    target_item = TextField(css_select='tr.athing')
    title = TextField(css_select='a.storylink')
    url = AttrField(css_select='a.storylink', attr='href')

class HackerNewsSpider(Spider):
    start_urls = [f'https://news.ycombinator.com/news?p={index}' for index in range(3)]

    async def parse(self, response):
        async for item in HackerNewsItem.get_items(html=response.html):
            yield item

    async def process_item(self, item: HackerNewsItem):
        """Ruia build-in method"""
        async with aiofiles.open('./hacker_news.txt', 'a') as f:
            await f.write(str(item.title) + '\n')

aiofiles is a third-party library to operate files in asynchronous way. It provides APIs the same as python standard open function.

Now, we have written a spider, and time to start crawling.

import aiofiles

from ruia import Spider, Item, TextField, AttrField


class HackerNewsItem(Item):
    target_item = TextField(css_select='tr.athing')
    title = TextField(css_select='a.storylink')
    url = AttrField(css_select='a.storylink', attr='href')

class HackerNewsSpider(Spider):
    start_urls = [f'https://news.ycombinator.com/news?p={index}' for index in range(3)]

    async def parse(self, response):
        async for item in HackerNewsItem.get_items(html=response.html):
            yield item

    async def process_item(self, item: HackerNewsItem):
        """Ruia build-in method"""
        async with aiofiles.open('./hacker_news.txt', 'a') as f:
            await f.write(str(item.title) + '\n')

if __name__ == '__main__':
    HackerNewsSpider.start()

Done. Now your code is more readable and maintainable.

Send Further Requests

I don't think that just crawling the catalogue of news satisfied you. Next we will crawl news itself. Hacker news gathers news from many websites, it's not easy to parse each article of it. For this example, we'll crawl Github Developer Documentation.

If you are a user of scrapy, perhaps you'd like this essay for migration: Write Spiders like Scrapy.

Ruia provides a better way to send further requests by new asynchronous syntax async/await. It provides more readability and is more flexible. In any parse method, just yield a coroutine, and the coroutine will be processed by ruia.

Here is a simple pseudo-code.

from ruia import Spider


class MySpider(Spider):
    async def parse(self, response):
        next_response = await self.request(f'{response.url}/next')
        yield self.parse_next_page(next_response, metadata='nothing')

    async def parse_next_page(self, response, metadata):
        print(response.html)

It works well, except you want to yield many coroutines in a for loop. Look at the following pseudo-code:

from ruia import Spider


class MySpider(Spider):
    async def parse(self, response):
        for i in range(10):
            response = await self.request(f'https://some.site/{i}')
            yield self.parse_next(response)

    async def parse_next(self, response):
        print(response.html)

You will find the requests in the for loop runs in a synchronous way! Oh, awful. To solve this problem, ruia provides a multiple_request method. Here is an example for Github Developer Documentation.

# Target: https://developer.github.com/v3/
from ruia import *


class CatalogueItem(Item):
    target_item = TextField(css_select='.sidebar-menu a')
    title = TextField(css_select='a')
    link = AttrField(css_select='a', attr='href')

    async def clean_link(self, value):
        return f'https://developer.github.com{value}'


class PageItem(Item):
    content = HtmlField(css_select='.content')


class GithubDeveloperSpider(Spider):
    start_urls = ['https://developer.github.com/v3/']
    concurrency = 5

    async def parse(self, response: Response):
        catalogue = []
        async for cat in CatalogueItem.get_items(html=response.html):
            if '#' in cat.link:
                continue
            catalogue.append(cat)
        urls = [page.link for page in catalogue][:10]
        async for response in self.multiple_request(urls, is_gather=True):
            title = catalogue[response.index].title
            yield self.parse_page(response, title)

    async def parse_page(self, response, title):
        item = await PageItem.get_item(html=response.html)
        print(title, len(item.content))


if __name__ == '__main__':
    GithubDeveloperSpider.start()

Our crawler starts with start_urls and parse method as usual. We get a list of urls. Then we call self.multiple_request method to send further requests.

multiple_request(urls, **kwargs) method requires a positional argument urls. It is a list of string. It also accept any other arguments like ruia.Request. Pay attention to use async for statement.

multiple_request method returns an asynchronous generator. It yields responses. You may want to use enumerate to get the index of responses like this:

async def parse(self, response):
    urls = [f'https://site.com/{page}' for page in range(10)]
    async for response in self.multiple_request(urls):
        pass

Then you will get an Exception, telling you that enumerate cannot process asynchronous generator. ruia provides a property for every response object: response.index. It is useful when you want to pass some context to the next parsing method. The order of responses currently is just the same as urls, but it's an unstable feature. Use response.index to get its position.

multiple_request has another argument is_gather, which indicates whether ruia should run the requests together or not. If is_gather=True, then the requests will run together. If not, the requests will run one by one.

is_gather=True is usually better, except one condition: we have a catalogue contains 1000 pages. If we use gather=True, we will get the response after 1000 requests. It may take too long before parsing.

Concurrency Control

Let's repeat the Github Developer spider.

# Target: https://developer.github.com/v3/
from ruia import *


class CatalogueItem(Item):
    target_item = TextField(css_select='.sidebar-menu a')
    title = TextField(css_select='a')
    link = AttrField(css_select='a', attr='href')

    async def clean_link(self, value):
        return f'https://developer.github.com{value}'


class PageItem(Item):
    content = HtmlField(css_select='.content')


class GithubDeveloperSpider(Spider):
    start_urls = ['https://developer.github.com/v3/']
    concurrency = 5

    async def parse(self, response: Response):
        catalogue = []
        async for cat in CatalogueItem.get_items(html=response.html):
            catalogue.append(cat)
        for page in catalogue[:20]:
            if '#' in page.link:
                continue
            yield Request(url=page.link, metadata={'title': page.title}, callback=self.parse_page)

    async def parse_page(self, response: Response):
        item = await PageItem.get_item(html=response.html)
        title = response.metadata['title']
        print(title, len(item.content))


if __name__ == '__main__':
    GithubDeveloperSpider.start()

This time, there's a line added:

    concurrency = 5

Here's a brief introduction about concurrency. Some websites are friendly to crawlers, while some are not. If you visit a website too frequently, you will be banned from the server. Besides, to be a good crawler, we should protect the server, rather than making it crash. Not every server can burden a huge spider.

To protect both, we have to control our concurrency. Concurrency means the connection numbers in a time. In this case, we set it to 5.

Let's have a short look on the log.

Output:
[2019:01:23 00:01:59]-ruia-INFO  spider : Spider started!
[2019:01:23 00:01:59]-ruia-WARNINGspider : ruia tried to use loop.add_signal_handler but it is not implemented on this platform.
[2019:01:23 00:01:59]-ruia-WARNINGspider : ruia tried to use loop.add_signal_handler but it is not implemented on this platform.
[2019:01:23 00:01:59]-Request-INFO  request: <GET: https://developer.github.com/v3/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/media/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/oauth_authorizations/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/auth/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/troubleshooting/>
[2019:01:23 00:02:01]-Request-INFO  request: <GET: https://developer.github.com/v3/previews/>
Overview 38490
[2019:01:23 00:02:02]-Request-INFO  request: <GET: https://developer.github.com/v3/versions/>
OAuth Authorizations API 66565
[2019:01:23 00:02:02]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/>
Media Types 8652
[2019:01:23 00:02:02]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/events/>
Troubleshooting 2551
[2019:01:23 00:02:02]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/events/types/>
API Previews 19537
[2019:01:23 00:02:02]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/feeds/>
Other Authentication Methods 6651
[2019:01:23 00:02:03]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/notifications/>
Versions 1344
Feeds 14090
[2019:01:23 00:02:03]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/starring/>
Activity 2178
[2019:01:23 00:02:04]-Request-INFO  request: <GET: https://developer.github.com/v3/activity/watching/>
[2019:01:23 00:02:05]-Request-INFO  request: <GET: https://developer.github.com/v3/checks/>
Events 11844
Starring 55228
[2019:01:23 00:02:05]-Request-INFO  request: <GET: https://developer.github.com/v3/checks/runs/>
[2019:01:23 00:02:05]-Request-INFO  request: <GET: https://developer.github.com/v3/checks/suites/>
Event Types & Payloads 1225037
Notifications 65679
Watching 35775
Checks 7379
Check Runs 116607
[2019:01:23 00:02:06]-ruia-INFO  spider : Stopping spider: ruia
Check Suites 115330
[2019:01:23 00:02:06]-ruia-INFO  spider : Total requests: 18
[2019:01:23 00:02:06]-ruia-INFO  spider : Time usage: 0:00:07.342048
[2019:01:23 00:02:06]-ruia-INFO  spider : Spider finished!

Focus on the first several lines.

[2019:01:23 00:01:54]-Request-INFO  request: <GET: https://developer.github.com/v3/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/media/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/oauth_authorizations/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/auth/>
[2019:01:23 00:02:00]-Request-INFO  request: <GET: https://developer.github.com/v3/troubleshooting/>
[2019:01:23 00:02:05]-Request-INFO  request: <GET: https://developer.github.com/v3/previews/>
Overview 38490
[2019:01:23 00:02:07]-Request-INFO  request: <GET: https://developer.github.com/v3/versions/>
OAuth Authorizations API 66565

The first request is at our requesting the catalogue page. Then, our spider send 5 requests at almost same time, at [00:02:00]. 5 seconds later, at [00:02:05], our spider receives a response, and then sent another request. The response was parsed immediately. 2 seconds later, at [00:02:07], our spider receives another response, and sent another request. Then, it parsed the response immediately.

That is to say, at any time, there are 5 connections between spider and server. That is concurrency control.

Hey, notice that our spider sent 5 requests at same time! Thanks to python's asyncio library, we can write asynchronous crawler easier and faster. Coroutines runs faster than multi-threadings.

Use Middleware

Ruia provides mainly two ways to enhance itself.

Firstly let's talk about middlewares. Middlewares are used to process a request before it's sending and to process a response after it's receiving In a word, it is something between your spider and server.

Here is a simple middleware named ruia-ua, it is used to automatically add random User-Agent to your requests.

Firstly, install ruia-ua.

pip install ruia-ua

Then, add it to your spider.

from ruia import AttrField, TextField, Item, Spider
from ruia_ua import middleware


class HackerNewsItem(Item):
    target_item = TextField(css_select='tr.athing')
    title = TextField(css_select='a.storylink')
    url = AttrField(css_select='a.storylink', attr='href')

    async def clean_title(self, value):
        return value


class HackerNewsSpider(Spider):
    start_urls = ['https://news.ycombinator.com/news?p=1', 'https://news.ycombinator.com/news?p=2']
    concurrency = 10

    async def parse(self, res):
        async for item in HackerNewsItem.get_items(html=res.html):
            print(item.title)


if __name__ == '__main__':
    HackerNewsSpider.start(middleware=middleware)

ruia.Spider has an argument middleware. It receives a list or a single middleware.

Use Plugin

If you want better control of your spider, try to use some plugins.

ruia-pyppeteer is a ruia plugin used for loading JavaScript.

Firstly, install ruia-pyppeteer.

pip install ruia_pyppeteer
# New features
pip install git+https://github.com/ruia-plugins/ruia-pyppeteer

Note

When you use load_js, it will download a recent version of Chromium (~100MB). This only happens once.

Here is a simple example to show how to load JavaScript.

import asyncio

from ruia_pyppeteer import PyppeteerRequest as Request

request = Request("https://www.jianshu.com/", load_js=True)
response = asyncio.get_event_loop().run_until_complete(request.fetch())
print(response.html)

Here is an example to use it in your spider:

from ruia import AttrField, TextField, Item

from ruia_pyppeteer import PyppeteerSpider as Spider
from ruia_pyppeteer import PyppeteerRequest as Request


class JianshuItem(Item):
    target_item = TextField(css_select='ul.list>li')
    author_name = TextField(css_select='a.name')
    author_url = AttrField(attr='href', css_select='a.name')

    async def clean_author_url(self, author_url):
        return f"https://www.jianshu.com{author_url}"


class JianshuSpider(Spider):
    start_urls = ['https://www.jianshu.com/']
    concurrency = 10
    # Load js on the first request
    load_js = True

    async def parse(self, response):
        async for item in JianshuItem.get_items(html=response.html):
            # Loading js by using PyppeteerRequest
            yield Request(url=item.author_url, load_js=self.load_js, callback=self.parse_item)

    async def parse_item(self, response):
        print(response)

if __name__ == '__main__':
    JianshuSpider.start()