Item Pipeline  After an item has been scraped by a spider, it is
sent to the Item Pipeline which process it through several
components that are executed sequentially.  Each item pipeline
component (sometimes referred as just “Item Pipeline”) is a
Python class that implements a simple method. They receive an
Item and perform an action over it, also deciding if the Item
should continue through the pipeline or be dropped and no longer
processed.  Typical use for item pipelines are:    • cleansing
HTML data   • checking for duplicates (and dropping them)   •
storing the scraped item in a database  Writing your own item
pipeline  Writing your own item pipeline is easy. Each item
pipeline component is a single Python class that must implement
the following method:  process_item(item, spider)  This method
is called for every item pipeline component and must either
return a Item (or any descendant class) object or raise a
DropItem exception. Dropped items are no longer processed by
further pipeline components.    • i