【scrapy】基礎知識

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Items

Item objects are simple containers used to collect the scraped data.They provide a dictionary-like api with a convenient syntax for declaring their available fields.

import scrapy;

class Product(scrapy.Item):

　　name=scrapy.Field()

　　price=scrapy.Field()

　　stock=scrapy.Field()

　　last_updated=scrapy.Field(serializer=str)

Extending Items

you can extend Items(to add more fields or to change some metadata for some fields)by declaring a subclass of your original Item.

class DiscountedProduct(Product):

　　discount_percent=scrapy.Field(serializer=str)

You can also extend fields metadata by using the previous field metadata and appending more values,or changind existing values.

class SpecificProduct(Product):

　　name=scrapy.Field(Product.fields[‘name‘],serializer=my_serializer)

Item Objects

1.class scrapy.item.Item([arg])

Return a new Item optionally initialized from the given argument

The only additional attribute provided by Items is:fields

2.Field objects

class scrapy.item.Field([arg])

The Field class is just an alias to the built-in dict class and doesn‘t provide any extra functionality or attributes.