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Handling Pagination and Following Links

In this tutorial, we will learn about handling pagination and following links when scraping with Scrapy. This is a crucial aspect to understand as most websites spread their data across multiple pages. Hence, to effectively scrape data, a web crawler needs to navigate through these pages.

Scrapy Basics​

Scrapy is a powerful Python framework for web scraping. It allows you to write spiders, which are programs that navigate through websites and scrape data.

Understanding Pagination​

Pagination is a common feature on websites, especially those with large amounts of data. It's a way of dividing content into several pages to make the data more manageable and user-friendly.

For example, an e-commerce site might have thousands of product listings. Instead of displaying all of those listings on one page, they're divided into pages, each containing a certain amount of listings.

To scrape data across multiple pages, Scrapy needs to follow the links to the next pages. This is done by finding the URL of the next page and sending a new request to that URL.

Here's a basic example of how to follow links in a Scrapy spider:

def parse(self, response):
    # Extract data from this page
    # ...

    next_page_url = response.css('a.next::attr(href)').get()
    if next_page_url is not None:
        yield scrapy.Request(response.urljoin(next_page_url))

In this example, the parse method extracts data from the page, then finds the URL of the next page. response.css('a.next::attr(href)').get() uses CSS selectors to find an a element with the class next, and get its href attribute, which is the URL. If the URL exists, it sends a new request to that URL.

Handling Pagination​

The process of following links can be repeated to navigate through all the pages of a website. This is how Scrapy handles pagination.

Here's an example of a Scrapy spider that follows links:

class MySpider(scrapy.Spider):
    name = 'myspider'
    start_urls = ['http://example.com']

    def parse(self, response):
        # Extract data from this page
        # ...

        next_page_url = response.css('a.next::attr(href)').get()
        if next_page_url is not None:
            yield scrapy.Request(response.urljoin(next_page_url), self.parse)

In this example, the spider starts at 'http://example.com', extracts data from the page, then follows the link to the next page. It continues this process for all the pages of the website.

The key here is the callback function to the scrapy.Request call. When Scrapy sends a request to a URL, it needs to know what function to use to parse the response. By passing self.parse as the callback function, we're telling Scrapy to use the same parse function to handle the response of the next page.

Conclusion​

Handling pagination and following links are fundamental aspects of web scraping. They allow a Scrapy spider to navigate through websites and scrape data across multiple pages. Practice with different websites and see how you can extract information from various pages. Happy scraping!