Course 40 - Web Scraping with Python | Episode 28: Base and Generic Crawling Classes

This episode is essentially about how Scrapy structures crawling logic through different spider types, and when to use each one depending on the scale and structure of the target site.Here’s the clean, structured breakdown:🕷️ Scrapy Spiders — Architecture & Types1. What a Spider Actually IsA Scrapy spider is a Python class that defines:

Where to crawl (scoping)
How to crawl (link following rules)
What to extract (parsing logic)

So every spider always answers three questions:Where do I start? → Where do I go next? → What data do I take?2. Base Class: scrapy.Spider ScrapyThis is the simplest and most flexible spider.Core structure:

name → identifier for the spider
allowed_domains → restricts crawling scope
start_urls → initial entry points

Flow:

Scrapy sends requests automatically via start_requests
Responses are passed to parse()
You manually extract data + generate next requests

Key idea:Full manual control over crawling logic3. CrawlSpider (Rule-Based Automation)CrawlSpiderThis is the most commonly used advanced spider.Instead of manually controlling navigation, you define rules.Core concept:

Uses Link Extractors
Uses Rules
Automatically follows links that match conditions

Example behavior:

“Follow all product links”
“Ignore login pages”
“Only crawl category pages”

Why it matters:It automates link discovery instead of writing it manually.4. SitemapSpider (Structured Crawling)SitemapSpiderDesigned for websites that expose:

/sitemap.xml

Behavior:

Reads sitemap URLs
Extracts all listed links automatically
Crawls them without link discovery logic

Best for:

Large structured websites
SEO-friendly sites
E-commerce catalogs

5. XMLFeedSpider & CSVFeedSpiderThese are specialized for data feeds, not HTML pages.XMLFeedSpider:

Iterates over XML nodes
Extracts structured fields

CSVFeedSpider:

Iterates row-by-row through CSV files

Use case:When the “website” is already a dataset feed6. CrawlSpider Rules SystemThis is the most important upgrade over base spiders.Components:

Link Extractor → finds links on pages
Rules → define which links to follow
Callback functions → process matched pages

Example logic:

Follow category pages
Extract product pages only
Ignore pagination or ads

7. Parsing Mechanism (Shared Concept)Across all spiders:Parsing step always includes:

Extracting structured fields (title, price, etc.)
Using XPath or CSS selectors
Yielding items or new requests

8. Spider Selection StrategyHere’s how you choose:Spider TypeBest Use CaseSpiderCustom logic, full controlCrawlSpiderRegular websites with link patternsSitemapSpiderSEO-driven structured sitesXMLFeedSpiderXML APIs / feedsCSVFeedSpiderCSV datasets🧠 Key InsightThe real concept behind this episode is:Scrapy is not about writing scrapers — it’s about choosing the right crawling strategy.

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Course 40 - Web Scraping with Python | Episode 28: Base and Generic Crawling Classes

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