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Item Pipeline

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.. module:: scrapy.contrib.pipeline
   :synopsis: Item Pipeline manager and built-in pipelines

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.

Item pipeline are usually implemented on each project. Typical usage for item pipelines are:

  • HTML cleansing
  • validation
  • persistence (storing the scraped item)

Writing your own item pipeline

Writing your own item pipeline is easy. Each item pipeline component is a single Python class that must define the following method:

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.. method:: process_item(domain, item)

domain is a string with the domain of the spider which scraped the item

item is a :class:`~scrapy.item.Item` with the item scraped

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This method is called for every item pipeline component and must either return a :class:`~scrapy.item.Item` (or any descendant class) object or raise a :exc:`~scrapy.core.exceptions.DropItem` exception. Dropped items are no longer processed by further pipeline components.

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Item pipeline example

Let's take a look at following hypothetic pipeline that adjusts the price attribute for those items that do not include VAT (price_excludes_vat attribute), and drops those items which don't contain a price:

from scrapy.core.exceptions import DropItem

class PricePipeline(object):

    vat_factor = 1.15

    def process_item(self, domain, item):
        if item['price']:
            if item['price_excludes_vat']:
                item['price'] = item['price'] * self.vat_factor
            return item
        else:
            raise DropItem("Missing price in %s" % item)

Item pipeline example with resources per domain

Sometimes you need to keep resources about the items processed grouped per domain, and delete those resource when a domain finish.

An example is a filter that looks for duplicate items, and drops those items that were already processed. Let say that our items has an unique id, but our spider returns multiples items with the same id:

from scrapy.xlib.pydispatch import dispatcher
from scrapy.core import signals
from scrapy.core.exceptions import DropItem

class DuplicatesPipeline(object):
    def __init__(self):
        self.domaininfo = {}
        dispatcher.connect(self.domain_opened, signals.domain_opened)
        dispatcher.connect(self.domain_closed, signals.domain_closed)

    def domain_opened(self, domain):
        self.duplicates[domain] = set()

    def domain_closed(self, domain):
        del self.duplicates[domain]

    def process_item(self, domain, item):
        if item.id in self.duplicates[domain]:
            raise DropItem("Duplicate item found: %s" % item)
        else:
            self.duplicates[domain].add(item.id)
            return item

Built-in Item Pipelines reference

Here is a list of item pipelines bundled with Scrapy.

File Export Pipeline

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Unknown directive type "module".

.. module:: scrapy.contrib.pipeline.fileexport

This pipeline exports all scraped items into a file, using different formats.

It is simple but convenient wrapper to use :doc:`Item Exporters <exporters>` as :ref:`Item Pipelines <topics-item-pipeline>`. If you need more custom/advanced functionality you can write your own pipeline or subclass the :doc:`Item Exporters <exporters>` .

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It supports the following settings:

If any mandatory setting is not set, this pipeline will be automatically disabled.

File Export Pipeline examples

Here are some usage examples of the File Export Pipeline.

To export all scraped items into a XML file:

EXPORT_FORMAT = 'xml'
EXPORT_FILE = 'scraped_items.xml'

To export all scraped items into a CSV file (without a headers line):

EXPORT_FORMAT = 'csv'
EXPORT_FILE = 'scraped_items.csv'

To export all scraped items into a CSV file (with a headers line):

EXPORT_FORMAT = 'csv_headers'
EXPORT_FILE = 'scraped_items_with_headers.csv'
EXPORT_FILEDS = ['name', 'price', 'description']

File Export Pipeline settings

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.. currentmodule:: scrapy.contrib.exporter

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.. setting:: EXPORT_FORMAT

EXPORT_FORMAT

The format to use for exporting. Here is a list of all available formats. Click on the respective Item Exporter to get more info.

This setting is mandatory in order to use the File Export Pipeline.

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.. setting:: EXPORT_FILE

EXPORT_FILE

The name of the file where the items will be exported. This setting is mandatory in order to use the File Export Pipeline.

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.. setting:: EXPORT_FIELDS

EXPORT_FIELDS

Default: None

The name of the item fields that will be exported. This will be use for the :attr:`~BaseItemExporter.fields_to_export` Item Exporter attribute. If None, all fields will be exported.

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.. setting:: EXPORT_EMPTY

EXPORT_EMPTY

Whether to export empty (non populated) fields. This will be used for the :attr:`~BaseItemExporter.export_empty_fields` Item Exporter attribute.

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.. setting:: EXPORT_ENCODING

EXPORT_ENCODING

The encoding to use for exporting. Ths will be used for the :attr:`~BaseItemExporter.encoding` Item Exporter attribute.

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