Extend a Scrapy ItemLoader with custom methods
问题 The Scrapy documentation lists all the built-in methods of ItemLoader instances and explains how to declare your own Item Loaders. However, any ItemLoaders you declare will apply to all processed items. You can modify their behavior a little with Item Loader Contexts, but this is frequently not granular enough. Suppose I have a Scrapy project where the spiders and items all inherit the same base spider and item loaders, but the spiders all contain site-specific logic with a handful of common