I'm trying to crawl through a webpage and extract a group of links then crawl through the webpages of those links and get the data by returning it through an item loader but having trouble. This is the code I have problem with in my spider class:
def parse(self, response):
#--initialize selector--
for s in response.css(SECTION_SELECTOR):
#--populate object attributes--
yield scrapy.Request( self.link, callback=self.parse_single )
def parse_single(self, response):
#--initialize selector--
for p in response.css(SINGLE_SELECTOR):
#--populate item_loader (l)--
yield l.load_item()
The problem with this approach is that only the items in the last s item are being returned, and the same items are iterated over and over when I save them as a csv file. The loop items in the second parse method are output as hoped with no duplicates.
If I try to switch the yield with return on the first parse method, only the first s item is executed, and again the second parse prints items to file as expected, but only the first s row is outputted with no duplicates.
Please someone explain to me how I can get the code to iterate over all the items in the first loop so they print in the second.
Related
I am using Scrapy with python to scrape a website and I face some difficulties with filling the item that I have created.
The products are properly scraped and everything is working well as long as the info is located within the response.xpath mentioned in the for loop.
'trend' and 'number' are properly added to the Item using ItemLoader.
However, the date of the product is not located within the response.xpath cited below but in the response.css as a title : response.css('title')
import scrapy
import datetime
from trends.items import Trend_item
from scrapy.loader import ItemLoader
#Initiate the spider
class trendspiders(scrapy.Spider):
name = 'milk'
start_urls = ['https://thewebsiteforthebestmilk/ireland/2022-03-16/7/']
def parse(self, response):
for milk_unique in response.xpath('/html/body/main/div/div[2]/div[1]/section[1]/div/div[3]/table/tbody/tr'):
l = ItemLoader(item=Milk_item(), selector=milk_unique, response=response)
l.add_css('milk', 'a::text')
l.add_css('number', 'span.small.text-muted::text')
return l.load_item()
How can I add the 'date' to my item please (found in response.css('title')?
I have tried to add l.add_css('date', "response.css('title')")in the for loop but it returns an error.
Should I create a new parsing function? If yes then how to send the info to the same Item?
I hope I’ve made myself clear.
Thank you very much for your help,
Since the date is outside of the selector you are using for each row, what you should do is extract that first before your for loop, since it doesn't need to be updated on each iteration.
Then with your item loader you can just use l.add_value to load it with the rest of the fields.
For example:
class trendspiders(scrapy.Spider):
name = 'trends'
start_urls = ['https://getdaytrends.com/ireland/2022-03-16/7/']
def parse(self, response):
date_str = response.xpath("//title/text()").get()
for trend_unique in response.xpath('/html/body/main/div/div[2]/div[1]/section[1]/div/div[3]/table/tbody/tr'):
l = ItemLoader(item=Trend_item(), selector=trend_unique, response=response)
l.add_css('trend', 'a::text')
l.add_css('number', 'span.small.text-muted::text')
l.add_value('date', date_str)
yield l.load_item()
If response.css('title').get() gives you the answer you need, why not use the same CSS with add_css:
l.add_css('date', 'title')
Also, .add_css('date', "response.css('title')") is invalid because the second argument a valid CSS selector.
I am trying this sample code
from scrapy.spiders import Spider, Request
import scrapy
class MySpider(Spider):
name = 'toscrapecom'
start_urls = ['http://books.toscrape.com/catalogue/page-1.html']
urls = (
'http://books.toscrape.com/catalogue/page-{}.html'.format(i + 1) for i in range(50)
)
def parse(self, response):
for url in self.urls:
return Request(url)
It crawls all the pages fine. However if I yield an item before the for loop then it crawls only the first page. (as shown below)
from scrapy.spiders import Spider, Request
import scrapy
class MySpider(Spider):
name = 'toscrapecom'
start_urls = ['http://books.toscrape.com/catalogue/page-1.html']
urls = (
'http://books.toscrape.com/catalogue/page-{}.html'.format(i + 1) for i in range(50)
)
def parse(self, response):
yield scrapy.item.Item()
for url in self.urls:
return Request(url)
But I can use yield Request(url) instead of return... and it scrapes the pages backwards from last page to first.
I would like to understand why return does not work anymore once an item is yielded? Can somebody explain this in a simple way?
You ask why the second code does not work, but I don’t think you fully understand why the first code works :)
The for loop of your first code only loops once.
What is happening is:
self.parse() is called for the URL in self.start_urls.
self.parse() gets the first (and only the first!) URL from self.urls, and returns it, exiting self.parse().
When a response for that first URL arrives, self.parse() gets called again, and this time it returns a request (only 1 request!) for the second URL from self.urls, because the previous call to self.parse() already consumed the first URL from it (self.urls is an iterator).
The last step repeats in a loop, but it is not the for loop that does it.
You can change your original code to this and it will work the same way:
def parse(self, response):
try:
return next(self.urls)
except StopIteration:
pass
Because to call items/requests it should be generator function.
You even cannot use yield and return in the same function with the same "meaning", it will raise SyntaxError: 'return' with argument inside generator.
The return is (almost) equivalent to raising StopIteration. In this topic Return and yield in the same function you can find very detailed explanation, with links specification.
For example I want to crawl three similar urls:
https://example.com/book1
https://example.com/book2
https://example.com/book3
What I want is in the pipeline.py, that I create 3 files named book1, book2 and book3, and write the 3 books' data correctly and separately
In the spider.py, I know the three books' name which as the file name, but not in the pipeline.py
They have a same structure, so I decide to code like below:
class Book_Spider(scrapy.Spider):
def start_requests(self):
for url in urls:
yield scrapy.Request(url, self.parse)
def parse(self, response):
# item handling
yield item
Now, how can I do?
Smith, If you want to know book name in pipeline.py. there are two options either you make a item field for book_file_name and populate it accordingly as you want. or you can extract it from url field which is also a item field and can access in pipline.py
I'd like to do something special to those each one of the landing urls in start_urls, and then the spider'd follow all the nextpages and crawl deeper. So my code's roughly like this:
def init_parse(self, response):
item = MyItem()
# extract info from the landing url and populate item fields here...
yield self.newly_parse(response)
yield item
return
parse_start_url = init_parse
def newly_parse(self, response):
item = MyItem2()
newly_soup = BeautifulSoup(response.body)
# parse, return or yield items
return item
The code won't work because spider only allows return item, request or None but I yield self.newly_parse, so how can I achieve this in scrapy?
My not so elegant solution:
put the init_parse function inside newly_parse and implement an is_start_url check in the beginning, if response.url is inside start_urls, we'll go through the init_parse procedure.
Another ugly solution
Separate out the code where # parse, return or yield items happens and make it a class method or generator, and call this method or generator both inside init_parse and newly_parse.
If you're going to yield multiple items under newly_parse your line under init_parse should be:
for item in self.newly_parse(response):
yield item
as self.newly_parse will return a generator which you will need to iterate through first as scrapy won't recognize it.
Disclaimer: I'm fairly new to Scrapy.
To put my question plainly: How can I retrieve an Item property from a link on a page and get the results back into the same Item?
Given the following sample Spider:
class SiteSpider(Spider):
site_loader = SiteLoader
...
def parse(self, response):
item = Place()
sel = Selector(response)
bl = self.site_loader(item=item, selector=sel)
bl.add_value('domain', self.parent_domain)
bl.add_value('origin', response.url)
for place_property in item.fields:
parse_xpath = self.template.get(place_property)
# parse_xpath will look like either:
# '//path/to/property/text()'
# or
# {'url': '//a[#id="Location"]/#href',
# 'xpath': '//div[#class="directions"]/span[#class="address"]/text()'}
if isinstance(parse_xpath, dict): # place_property is at a URL
url = sel.xpath(parse_xpath['url_elem']).extract()
yield Request(url, callback=self.get_url_property,
meta={'loader': bl, 'parse_xpath': parse_xpath,
'place_property': place_property})
else: # parse_xpath is just an xpath; process normally
bl.add_xpath(place_property, parse_xpath)
yield bl.load_item()
def get_url_property(self, response):
loader = response.meta['loader']
parse_xpath = response.meta['parse_xpath']
place_property = response.meta['place_property']
sel = Selector(response)
loader.add_value(place_property, sel.xpath(parse_xpath['xpath'])
return loader
I'm running these spiders against multiple sites, and most of them have the data I need on one page and it works just fine. However, some sites have certain properties on a sub-page (ex., the "address" data existing at the "Get Directions" link).
The "yield Request" line is really where I have the problem. I see the items move through the pipeline, but they're missing those properties that are found at other URLs (IOW, those properties that get to "yield Request"). The get_url_property callback is basically just looking for an xpath within the new response variable, and adding that to the item loader instance.
Is there a way to do what I'm looking for, or is there a better way? I would like to avoid making a synchronous call to get the data I need (if that's even possible here), but if that's the best way, then maybe that's the right approach. Thanks.
If I understand you correctly, you have (at least) two different cases:
The crawled page links to another page containing the data (1+ further request necessary)
The crawled page contains the data (No further request necessary)
In your current code, you call yield bl.load_item() for both cases, but in the parse callback. Note that the request you yield is executed some later point in time, thus the item is incomplete and that's why you're missing the place_property key from the item for the first case.
Possible Solution
A possible solution (If I understood you correctly) Is to exploit the asynchronous behavior of Scrapy. Only minor changes to your code are involved.
For the first case, you pass the item loader to another request, which will then yield it. This is what you do in the isinstance if clause. You'll need to change the return value of the get_url_property callback to actually yield the loaded item.
For the second case, you can return the item directly,
thus simply yield the item in the else clause.
The following code contains the changes to your example.
Does this solve your problem?
def parse(self, response):
# ...
if isinstance(parse_xpath, dict): # place_property is at a URL
url = sel.xpath(parse_xpath['url_elem']).extract()
yield Request(url, callback=self.get_url_property,
meta={'loader': bl, 'parse_xpath': parse_xpath,
'place_property': place_property})
else: # parse_xpath is just an xpath; process normally
bl.add_xpath(place_property, parse_xpath)
yield bl.load_item()
def get_url_property(self, response):
loader = response.meta['loader']
# ...
loader.add_value(place_property, sel.xpath(parse_xpath['xpath'])
yield loader.load_item()
Related to that problem is the question of chaining requests, for which I have noted a similar solution.