How to use Python scrapy for myltiple URL's - scrapy

Question

my question is similar to this post:
How to use scrapy for Amazon.com links after "Next" Button?
I want my crawler to traverse through all "Next" links. I've searched a lot, but most people ether focus on how to parse the ULR or simply put all URL's in the initial URL list.
So far, I am able to visit the first page and parse the next page's link. But I don't know how to visit that page using the same crawler(spider). I tried to append the new URL into my URL list, it does appended (I checked the length), but later it doesn't visit the link. I have no idea why...
Note that in my case, I only know the first page's URL. Second page's URL can only be obtained after visiting the first page. The same, (i+1)'th page's URL is hidden in the i'th page.
In the parse function, I can parse and print the correct next page link URL. I just don't know how to visit it.
Please help me. Thank you!
import scrapy
from bs4 import BeautifulSoup
class RedditSpider(scrapy.Spider):
name = "test2"
allowed_domains = ["http://www.reddit.com"]
urls = ["https://www.reddit.com/r/LifeProTips/search?q=timestamp%3A1427232122..1437773560&sort=new&restrict_sr=on&syntax=cloudsearch"]
def start_requests(self):
for url in self.urls:
yield scrapy.Request(url, self.parse, meta={
'splash': {
'endpoint': 'render.html',
'args': { 'wait': 0.5 }
}
})
`
def parse(self, response):
page = response.url[-10:]
print(page)
filename = 'reddit-%s.html' % page
#parse html for next link
soup = BeautifulSoup(response.body, 'html.parser')
mydivs = soup.findAll("a", { "rel" : "nofollow next" })
link = mydivs[0]['href']
print(link)
self.urls.append(link)
with open(filename, 'wb') as f:
f.write(response.body)
Update
Thanks to Kaushik's answer, I figured out how to make it work. Though I still don't know why my original idea of appending new URL's doesn't work...
The updated code is as follow:
import scrapy
from bs4 import BeautifulSoup
class RedditSpider(scrapy.Spider):
name = "test2"
urls = ["https://www.reddit.com/r/LifeProTips/search?q=timestamp%3A1427232122..1437773560&sort=new&restrict_sr=on&syntax=cloudsearch"]
def start_requests(self):
for url in self.urls:
yield scrapy.Request(url, self.parse, meta={
'splash': {
'endpoint': 'render.html',
'args': { 'wait': 0.5 }
}
})
def parse(self, response):
page = response.url[-10:]
print(page)
filename = 'reddit-%s.html' % page
with open(filename, 'wb') as f:
f.write(response.body)
#parse html for next link
soup = BeautifulSoup(response.body, 'html.parser')
mydivs = soup.findAll("a", { "rel" : "nofollow next" })
if len(mydivs) != 0:
link = mydivs[0]['href']
print(link)
#yield response.follow(link, callback=self.parse)
yield scrapy.Request(link, callback=self.parse)

Answer 1

What you require is explained very well in the Scrapy docs . I don't think you would need any other explanation other than that. Suggest going through it once for better understanding.
A brief explanation first though:
To follow a link to the next page, Scrapy provides many methods. The most basic methods is using the http.Request method
Request object :
class scrapy.http.Request(url[, callback,
method='GET', headers, body, cookies, meta, encoding='utf-8',
priority=0, dont_filter=False, errback, flags])
>>> yield scrapy.Request(url, callback=self.next_parse)
url (string) – the URL of this request
callback (callable) – the function that will be called with the response of this request (once its downloaded) as its first parameter.
For convenience though, Scrapy has inbuilt shortcut for creating Request objects by using response.follow where the url can be an absolute path or a relative path.
follow(url, callback=None, method='GET', headers=None, body=None,
cookies=None, meta=None, encoding=None, priority=0, dont_filter=False,
errback=None)
>>> yield response.follow(url, callback=self.next_parse)
In case if you have to move through to the next link by passing values to a form or any other type of input field, you can use the Form Request objects. The FormRequest class extends the base Request with functionality
for dealing with HTML forms. It uses lxml.html forms to pre-populate
form fields with form data from Response objects.
Form Request object
from_response(response[, formname=None,
formid=None, formnumber=0, formdata=None, formxpath=None,
formcss=None, clickdata=None, dont_click=False, ...])
If you want to simulate a HTML Form POST in your spider and send a couple of key-value fields, you can return a FormRequest object (from your spider) like this:
return [FormRequest(url="http://www.example.com/post/action",
formdata={'name': 'John Doe', 'age': '27'},
callback=self.after_post)]
Note : If a Request doesn’t specify a callback, the spider’s parse() method will be used. If exceptions are raised during processing, errback is called instead.