Develop Reference

How to give scrapy spider a new task only once the current one has received a response from the server

I have a list of entries in a database that each corresponds to some scraping task. Only once one is finished, do I want the spider to continue to the next one. Here is some pseudocode that gives the idea of what I want to do though it is not exactly what I want because it uses a while loop creating a massive backlog of entries waiting to be processed.
def start_requests(self):
while True:
rec = GetDocumentAndMarkAsProcessing()
if rec == None:
break;
script = getScript(rec)
yield SplashRequest(..., callback=self.parse, endpoint="execute",
args={
'lua_source': script
}
)
def parse(self, response):
... store results in database ...
How can I make scrapy work on the next entry only when it has received a response from the previous SplashRequest for the previous entry?
I am not sure if simple callback functions would be enough to do the trick or if I need something more sophisticated.

All I needed to do was explicitly call another request with yield in the parse function with parse as the callback itself. So in the end I have something like this:
def start_requests(self):
rec = GetDocumentAndMarkAsProcessing()
script = getScript(rec)
yield SplashRequest(..., callback=self.parse, endpoint="execute",
args={
'lua_source': script
}
)
def parse(self, response):
... store results in database ...
rec = GetDocumentAndMarkAsProcessing()
script = getScript(rec)
yield SplashRequest(..., callback=self.parse, endpoint="execute",
args={
'lua_source': script
}
)

I believe you might be able to achieve this by setting CONCURRENT_REQUESTS to 1 in your settings.py. That will make it so the crawler only sends one request at a time, although I admit I am not sure how the timing works on the second request - whether it sends it when the callback is finished executing or when the response is retrieved.

Unable to force scrapy to make a callback using the url that got redirected

I've created a python script using scrapy to scrape some information available in a certain webpage. The problem is the link I'm trying with gets redirected very often. However, when I try few times using requests, I get the desired content.
In case of scrapy, I'm unable to reuse the link because I found it redirecting no matter how many times I try. I can even catch the main url using response.meta.get("redirect_urls")[0] meant to be used resursively within parse method. However, it always gets redirected and as a result callback is not taking place.
This is my current attempt (the link used within the script is just a placeholder):
import scrapy
from scrapy.crawler import CrawlerProcess
class StackoverflowSpider(scrapy.Spider):
handle_httpstatus_list = [301, 302]
name = "stackoverflow"
start_url = 'https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean'
def start_requests(self):
yield scrapy.Request(self.start_url,meta={"lead_link":self.start_url},callback=self.parse)
def parse(self,response):
if response.meta.get("lead_link"):
self.lead_link = response.meta.get("lead_link")
elif response.meta.get("redirect_urls"):
self.lead_link = response.meta.get("redirect_urls")[0]
try:
if response.status!=200 :raise
if not response.css("[itemprop='text'] > h2"):raise
answer_title = response.css("[itemprop='text'] > h2::text").get()
print(answer_title)
except Exception:
print(self.lead_link)
yield scrapy.Request(self.lead_link,meta={"lead_link":self.lead_link},dont_filter=True, callback=self.parse)
if __name__ == "__main__":
c = CrawlerProcess({
'USER_AGENT': 'Mozilla/5.0',
})
c.crawl(StackoverflowSpider)
c.start()
Question: How can I force scrapy to make a callback using the url that got redirected?

As far as I understand, you want to scrape a link until it stops redirecting and you finally get http status 200
If yes, then you have to first remove handle_httpstatus_list = [301, 302] from your code
Then create a CustomMiddleware in middlewares.py
class CustomMiddleware(object):
def process_response(self, request, response, spider):
if not response.css("[itemprop='text'] > h2"):
logging.info('Desired text not found so re-scraping' % (request.url))
req = request.copy()
request.dont_filter = True
return req
if response.status in [301, 302]:
original_url = request.meta.get('redirect_urls', [response.url])[0]
logging.info('%s is redirecting to %s, so re-scraping it' % (request._url, request.url))
request._url = original_url
request.dont_filter = True
return request
return response
Then your spider should look like something this
class StackoverflowSpider(scrapy.Spider):
name = "stackoverflow"
start_url = 'https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean'
custom_settings = {
'DOWNLOADER_MIDDLEWARES': {
'YOUR_PROJECT_NAME.middlewares.CustomMiddleware': 100,
}
}
def start_requests(self):
yield scrapy.Request(self.start_url,meta={"lead_link":self.start_url},callback=self.parse)
def parse(self,response):
answer_title = response.css("[itemprop='text'] > h2::text").get()
print(answer_title)
If you tell me which site you are scraping then I can help you out, you can email me as well which is on my profile

You may want to see this.
If you need to prevent redirecting it is possible by request meta:
request = scrapy.Request(self.start_url,meta={"lead_link":self.start_url},callback=self.parse)
request.meta['dont_redirect'] = True
yield request
Due to documentation this is a way to stop redirecting.

Unable to use proxies one by one until there is a valid response

I've written a script in python's scrapy to make a proxied requests using either of the newly generated proxies by get_proxies() method. I used requests module to fetch the proxies in order to reuse them in the script. However, the problem is the proxy my script chooses to use may not be the good one always so sometimes it doesn't fetch valid response.
How can I let my script keep trying with different proxies until there is a valid response?
My script so far:
import scrapy
import random
import requests
from itertools import cycle
from bs4 import BeautifulSoup
from scrapy.http.request import Request
from scrapy.crawler import CrawlerProcess
class ProxySpider(scrapy.Spider):
name = "sslproxies"
check_url = "https://stackoverflow.com/questions/tagged/web-scraping"
proxy_link = "https://www.sslproxies.org/"
def start_requests(self):
proxylist = self.get_proxies()
random.shuffle(proxylist)
proxy_ip_port = next(cycle(proxylist))
print(proxy_ip_port) #Checking out the proxy address
request = scrapy.Request(self.check_url, callback=self.parse,errback=self.errback_httpbin,dont_filter=True)
request.meta['proxy'] = "http://{}".format(proxy_ip_port)
yield request
def get_proxies(self):
response = requests.get(self.proxy_link)
soup = BeautifulSoup(response.text,"lxml")
proxy = [':'.join([item.select_one("td").text,item.select_one("td:nth-of-type(2)").text]) for item in soup.select("table.table tbody tr") if "yes" in item.text]
return proxy
def parse(self, response):
print(response.meta.get("proxy")) #Compare this to the earlier one whether they both are the same
def errback_httpbin(self, failure):
print("Failure: "+str(failure))
if __name__ == "__main__":
c = CrawlerProcess({
'USER_AGENT': 'Mozilla/5.0',
'DOWNLOAD_TIMEOUT' : 5,
})
c.crawl(ProxySpider)
c.start()
PS My intension is to seek any solution the way I've started here.

As we know http response needs to pass all middlewares in order to reach spider methods.
It means that only requests with valid proxies can proceed to spider callback functions.
In order to use valid proxies we need to check ALL proxies first and after that choose only from valid proxies.
When our previously chosen proxy doesn't work anymore - we mark this proxy as not valid and choose new one from remaining valid proxies in spider errback.
import scrapy
from scrapy.crawler import CrawlerProcess
from scrapy.http.request import Request
class ProxySpider(scrapy.Spider):
name = "sslproxies"
check_url = "https://stackoverflow.com/questions/tagged/web-scraping"
proxy_link = "https://www.sslproxies.org/"
current_proxy = ""
proxies = {}
def start_requests(self):
yield Request(self.proxy_link,callback=self.parse_proxies)
def parse_proxies(self,response):
for row in response.css("table#proxylisttable tbody tr"):
if "yes" in row.extract():
td = row.css("td::text").extract()
self.proxies["http://{}".format(td[0]+":"+td[1])]={"valid":False}
for proxy in self.proxies.keys():
yield Request(self.check_url,callback=self.parse,errback=self.errback_httpbin,
meta={"proxy":proxy,
"download_slot":proxy},
dont_filter=True)
def parse(self, response):
if "proxy" in response.request.meta.keys():
#As script reaches this parse method we can mark current proxy as valid
self.proxies[response.request.meta["proxy"]]["valid"] = True
print(response.meta.get("proxy"))
if not self.current_proxy:
#Scraper reaches this code line on first valid response
self.current_proxy = response.request.meta["proxy"]
#yield Request(next_url, callback=self.parse_next,
# meta={"proxy":self.current_proxy,
# "download_slot":self.current_proxy})
def errback_httpbin(self, failure):
if "proxy" in failure.request.meta.keys():
proxy = failure.request.meta["proxy"]
if proxy == self.current_proxy:
#If current proxy after our usage becomes not valid
#Mark it as not valid
self.proxies[proxy]["valid"] = False
for ip_port in self.proxies.keys():
#And choose valid proxy from self.proxies
if self.proxies[ip_port]["valid"]:
failure.request.meta["proxy"] = ip_port
failure.request.meta["download_slot"] = ip_port
self.current_proxy = ip_port
return failure.request
print("Failure: "+str(failure))
if __name__ == "__main__":
c = CrawlerProcess({
'USER_AGENT': 'Mozilla/5.0',
'COOKIES_ENABLED': False,
'DOWNLOAD_TIMEOUT' : 10,
'DOWNLOAD_DELAY' : 3,
})
c.crawl(ProxySpider)
c.start()

you need write a downloader middleware, to install a process_exception hook, scrapy calls this hook when exception raised. in the hook, you could return a new Request object, with dont_filter=True flag, to let scrapy reschedule the request until it succeeds.
in the meanwhile, you could verify response extensively in process_response hook, check the status code, response content etc., and reschedule request as necessary.
in order to change proxy easily, you should use built-in HttpProxyMiddleware, instead of tinker with environ:
request.meta['proxy'] = proxy_address
take a look at this project as an example.

Getting a New ASP.NET Session ID after Expiration in Scrapy

I have written a scraper in Scrapy 1.5 that successfully navigates to a webpage (running ASP.NET running on IIS version 8.5), submits a form, and then gets to scraping. After a few hours, all of the pages start returning blank data. I believe that my ASP.NET session id is expiring when this happens. I can never make it through the entire table (several thousand pages) while crawling at a respectful rate, but the table doesn't change from session to session. My approach was to scrape until the pages were returned blank, then go back to the form submission page and resubmit the form. I am keeping track of the page number so that I can pick up where I left off. The problem is that when I resubmit the form, the pages are still returned blank. If I stop the scraper, and set the count variable manually to the last page scraped, it works fine when I restart the scraper. Using fiddler I can see that the only thing that is different is that I have a new ASP.NET session id. So my question is, how can I clear out my ASP.NET session id so that I am given a new one and I can continue scraping? Here is a redacted version of the spider:
class assessorSpider(scrapy.Spider):
name = 'redacted'
allowed_domains = ['redacted.redacted']
start_urls = ['http://redacted.redacted/search.aspx']
base_url = start_urls[0]
rows_selector = '#T1 > tbody:nth-child(3) > tr'
numberOfPages = -1
count = 1
def parse(self, response):
#ASP.NET Session Id gets stored in the headers after initial search
frmdata = {'id':'frmSearch', 'SearchField':'%','cmdGo':'Go'}
yield scrapy.FormRequest(url = self.base_url, formdata = frmdata, callback = self.parse_index)
self.log('Search submitted')
def parse_index(self, response):
self.log('proceeding to next page')
rows = response.css(self.rows_selector)
if (len(rows) < 50 and self.count != self.numberOfPages):
self.log('Deficient rows. Resubmitting')
yield scrapy.Request(callback=self.parse, url = self.base_url, headers='')
self.log('Ready to yield value')
for row in rows:
value = {
#a whole bunch of css selectors
}
yield value
if self.numberOfPages == -1:
self.numberOfPages = response.css('a.button::attr(href)')[2].extract().split('=')[-1]
self.count = self.count + 1
if self.count <= self.numberOfPages:
self.log( self.base_url + '?page=' + str(self.count))
yield scrapy.Request(callback=self.parse_index, url = self.base_url + '?page=' + str(self.count))
Note: I have read that making a request with an expired ASP.NET session id should result in a new one being issued (depending on how the site is set up), so it is possible that scrapy is not accepting the new session id. I am not sure how to diagnose this issue.

There are two things that come to mind:
1) Your "start a fresh session" request might be getting rejected by the downloader: By default, it filters URLs that it's already seen, such as your base url. Try yield scrapy.Request(callback=self.parse, url = self.base_url, dont_filter=True, headers='') in your "reset the session request"
2) If that doesn't work (or perhaps in addition to):
I'm pretty new to Scrapy and Python, so there might be a more direct method to "reset your cookies" but specifying a fresh cookiejar should work.
https://doc.scrapy.org/en/latest/topics/downloader-middleware.html#multiple-cookie-sessions-per-spider
The cookiejar is essentially a dict-like object that is tracking your current session's cookies. You can specify the cookiejar key by using meta.
# Set up a new session if bad news:
if (len(rows) < 50 and self.count != self.numberOfPages):
self.log('Deficient rows. Resubmitting')
yield scrapy.Request(
callback=self.parse,
url=self.base_url,
dont_filter=True,
meta={
# Since you are already tracking a counter,
# this might make for a reasonable "next cookiejar id"
'cookiejar': self.count
}
)
Now that you are specifying a new cookiejar, you are in a new session. You must take account for this in your other requests, checking whether a cookiejar is set, and continuing to pass this value. Otherwise you end up back in the default cookiejar. It might be easiest to manage this expectation from the very beginning by defining start_requests:
def start_requests(self):
return [
scrapy.Request(
url,
dont_filter=True,
meta={'cookiejar': self.count}
) for url in self.start_urls
]
Now your other request objects just need to implement the following pattern to "stay in the same session", such as in your parse method:
yield scrapy.FormRequest(
url = self.base_url,
formdata = frmdata,
callback = self.parse_index,
meta={
'cookiejar': response.meta.get('cookiejar')
}
)

How to redirect after form post with scrapy_splash package?

I'm using Python, Scrapy, Splash, and the scrapy_splash package to scrap a website.
I'm able to log in using the SplashRequest object in scrapy_splash.
Login creates a cookie which gives me access to a portal page. To this point all works.
On the portal page, there is a form element wrapping a number of buttons. When clicked the action URL gets updated and a form submission is triggered. The form submission results in a 302 redirect.
I tried the same approach with the SplashRequest, however, I'm unable to capture the SSO query parameter that is returned with the redirect. I've tried to read the header Location parameter without success.
I've also tried using lua scripts in combination with the SplashRequest object, however, I'm still unable to access the redirect Location object.
Any guidance would be greatly appreciated.
I realize there are other solutions (i.e. selenium) available however the above tech is what we are using across a large number of other scripts and I hesitate to add new tech for this specific use case.
# Lua script to capture cookies and SSO query parameter from 302 Redirect
lua_script = """
function main(splash)
if splash.args.cookies then
splash:init_cookies(splash.args.cookies)
end
assert(splash:go{
splash.args.url,
headers=splash.args.headers,
http_method=splash.args.http_method,
body=splash.args.body,
formdata=splash.args.formdata
})
assert(splash:wait(0))
local entries = splash:history()
local last_response = entries[#entries].response
return {
url = splash:url(),
headers = last_response.headers,
http_status = last_response.status,
cookies = splash:get_cookies(),
html = splash:html(),
}
end
"""
def parse(self, response):
yield SplashRequest(
url='https://members.example.com/login',
callback=self.portal_page,
method='POST',
endpoint='execute',
args={
'wait': 0.5,
'lua_source': self.lua_script,
'formdata': {
'username': self.login,
'password': self.password
},
}
)
def portal_page(self, response):
yield SplashRequest(
url='https://data.example.com/portal'
callback=self.data_download,
args={
'wait': 0.5,
'lua_source': self.lua_script,
'formdata': {}
},
)
def data_download(self, response):
print(response.body.decode('utf8')

I updated the question above with a working example.
I changed a few things however the problem I was having was directly related to missing the splash:init_cookies(splash.args.cookies) reference.
I also converted from using SplashFormRequest to SplashRequest, refactored the splash:go block and removed a reference to the specific form.
Thanks again #MikhailKorobov for your help.