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Spider

Spider is the entrypoint of the crawler program. It combines Item, Middleware, Request and other models, to build a strong crawler for you. You should focus on the following two functions:

  • Spider.start: the entrypoint
  • parse: The first parse function, required for subclass of Spider

Core arguments

Spider.start arguments:

  • after_start: a hook after starting the crawler
  • before_stop: a hook before starting the crawler
  • middleware: Middleware class, can be an object of Middleware(), or a list of Middleware()
  • loop: event loop

Usage

import aiofiles

from ruia import AttrField, TextField, Item, Spider


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']

    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()

Controlling the max number of concurrency

Define an attribute concurrency at the subclass of Spider. Here is an example:

import ruia


class MySpider(ruia.Spider):

    start_urls = ['https://news.ycombinator.com']
    concurrency = 3

    async def parse(self, res):
        pass

How It Works?

Spider will read links in start_urls, and maintains a asynchronous queue. The queue is a producer consumer model, and the loop will run until no more request functions.