Python Rapid Development of Scrapy, a Distributed Search Engine-craw scrapy item loader

Create autocrawler files with commands

Creating crawler files is based on the master scrapy to create crawler files

Scrapy genspider-l View scrapy's available master for creating crawler files

Available templates: Master description
Create basic crawler files

crawl Create Autocrawler Files
Create crawler files for crawling csv data

Create crawling xml data crawler files

Create a base master crawler, the same goes for the rest

Scrapy genspider-t master name crawler file name to crawl the domain name to create a base master crawler, the same as other
For example: scrapy genspider-t crawl Lagou

First, configure to receive data fields

default_output_processor = TakeFirst() defaults to use the ItemLoader class to load the items container class to fill in the data, which is a list type and can be retrieved from the list through the TakeFirst() method.

Input_processor = MapCompose (preprocessing function) sets the preprocessing function for the data field, which can be multiple functions

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# -*- coding: utf-8 -*-

# Define here the models for your scraped items
# See documentation in:
#Item. py, the file is specially used to receive data information from the crawler, which is equivalent to container file.

import scrapy
from scrapy.loader.processors import MapCompose,TakeFirst
from scrapy.loader import ItemLoader                #Importing the ItemLoader class also loads the items container class to fill in the data.

class LagouItemLoader(ItemLoader):                  #Custom Loader inherits the ItemLoader class and calls it on the crawler page to populate the data into the Item class
    default_output_processor = TakeFirst()          #By default, the ItemLoader class is used to load the items container class to fill in the data, which is a list type. The contents of the list can be obtained through the TakeFirst() method.

def tianjia(value):                                 #Custom Data Preprocessing Function
    return 'Hawking Recording Network'+value                        #Return the processed data to Item

class LagouItem(scrapy.Item):                       #Setting the information container class that the crawler gets
    title = scrapy.Field(                           #Receiving title information from Crawlers
        input_processor = MapCompose(tianjia),      #When the name of the data preprocessing function is passed into the MapCompose method for processing, the formal parameter value of the data preprocessing function automatically receives the field title.

The second step is to write the automatic crawler and use the ItemLoader class to load the items container class to fill the data.

Rule() Sets crawler rules
LinkExtractor() Sets url rules
callback='callback function name'
follow=True means to go deeper in crawling pages

LinkExtractor() makes rule judgment on the url acquired by the crawler
Allo= r'jobs/'is a regular expression, which means that only if it conforms to this url format can it be extracted.
deny= r'jobs/'is a regular expression that indicates that it conforms to this url format, does not extract and discard, as opposed to allow.
Allo_domains= indicates that the connection under this domain name is extracted
deny_domains= denotes that connections under this domain name are not withdrawn and discarded
The restrict_xpaths= xpath expression indicates that the crawler can use the xpath expression to restrict it to extract only the URL s of the specified area of a page
Rest_css= CSS selector, which means that the crawler can use CSS selector to restrict the URL to extract only one page's specified area
Tags='a'means that the crawler searches for url through a tag, which is set by default and can be done by default.
Attrs='href'denotes the href attribute of the tag a, which has been set by default and can be done by default.

Inheriting ItemLoader class with custom Loader class, loading items container class to fill data

ItemLoader() instantiates an ItemLoader object to load the ItemLoader container class and fill in the data, the same usage as ItemLoader inherited by custom Loader
First parameter: Note parentheses for the items container class to fill in the data.
The second parameter is response:

Method under ItemLoader object:
The add_xpath('field name','xpath expression') method fills the specified field with the data obtained from the XPath expression
The add_css('field name','css selector') method fills in the specified field with the data obtained by the CSS selector
The add_value('field name', string content) method fills the specified string data into the specified field
The load_item() method has no parameters and generates all the data. After the load_item() method is yield ed, the data is filled in the fields of the specified class of the items container.

Crawler files

# -*- coding: utf-8 -*-
import scrapy
from scrapy.linkextractors import LinkExtractor
from scrapy.spiders import CrawlSpider, Rule
from adc.items import LagouItem,LagouItemLoader  #Import items container classes, and ItemLoader classes

class LagouSpider(CrawlSpider):                     #Create reptiles
    name = 'lagou'                                  #Reptilian name
    allowed_domains = ['']             #Initial domain name
    start_urls = [''] start url

    rules = (
        #Configuration crawl list page rule
        Rule(LinkExtractor(allow=('ggwa/.*')), follow=True),

        #Configuration crawl content page rule
        Rule(LinkExtractor(allow=('post/\d+.html.*')), callback='parse_job', follow=True),

    def parse_job(self, response):                  #Callback function, note: Because the source code of the CrawlS template creates the parse callback function, remember that we can't create the function with the parse name.
        #Using ItemLoader class to load items container class to fill data
        item_loader = LagouItemLoader(LagouItem(), response=response)
        article_item = item_loader.load_item()

        yield article_item

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Schematic diagram of file and crawler file

Keywords: Python xml REST network

Added by broseph on Thu, 05 Sep 2019 06:50:35 +0300