Item Exporters

Once you have scraped your Items, you often want to persist or export those items, to use the data in some other application. That is, after all, the whole purpose of the scraping process.

For this purpose Scrapy provides a collection of Item Exporters for different output formats, such as XML, CSV or JSON.

Using Item Exporters

If you are in a hurry, and just want to use an Item Exporter to output scraped data see the Feed exports. Otherwise, if you want to know how Item Exporters work or need more custom functionality (not covered by the default exports), continue reading below.

In order to use an Item Exporter, you must instantiate it with its required args. Each Item Exporter requires different arguments, so check each exporter documentation to be sure, in Built-in Item Exporters reference. After you have instantiated your exporter, you have to:

1. call the method start_exporting() in order to signal the beginning of the exporting process

2. call the export_item() method for each item you want to export

3. and finally call the finish_exporting() to signal the end of the exporting process

Here you can see an Item Pipeline which uses an Item Exporter to export scraped items to different files, one per spider:

from scrapy import signals
from scrapy.contrib.exporter import XmlItemExporter

class XmlExportPipeline(object):

    def __init__(self):
        self.files = {}

     @classmethod
     def from_crawler(cls, crawler):
         pipeline = cls()
         crawler.signals.connect(pipeline.spider_opened, signals.spider_opened)
         crawler.signals.connect(pipeline.spider_closed, signals.spider_closed)
         return pipeline

    def spider_opened(self, spider):
        file = open('%s_products.xml' % spider.name, 'w+b')
        self.files[spider] = file
        self.exporter = XmlItemExporter(file)
        self.exporter.start_exporting()

    def spider_closed(self, spider):
        self.exporter.finish_exporting()
        file = self.files.pop(spider)
        file.close()

    def process_item(self, item, spider):
        self.exporter.export_item(item)
        return item

Serialization of item fields

By default, the field values are passed unmodified to the underlying serialization library, and the decision of how to serialize them is delegated to each particular serialization library.

However, you can customize how each field value is serialized before it is passed to the serialization library.

There are two ways to customize how a field will be serialized, which are described next.

1. Declaring a serializer in the field

You can declare a serializer in the field metadata. The serializer must be a callable which receives a value and returns its serialized form.

Example:

from scrapy.item import Item, Field

def serialize_price(value):
   return '$ %s' % str(value)

class Product(Item):
    name = Field()
    price = Field(serializer=serialize_price)

2. Overriding the serialize_field() method

You can also override the serialize_field() method to customize how your field value will be exported.

Make sure you call the base class serialize_field() method after your custom code.

Example:

from scrapy.contrib.exporter import XmlItemExporter

class ProductXmlExporter(XmlItemExporter):

    def serialize_field(self, field, name, value):
        if field == 'price':
            return '$ %s' % str(value)
        return super(Product, self).serialize_field(field, name, value)

Built-in Item Exporters reference

Here is a list of the Item Exporters bundled with Scrapy. Some of them contain output examples, which assume you’re exporting these two items:

Item(name='Color TV', price='1200')
Item(name='DVD player', price='200')

BaseItemExporter

class scrapy.contrib.exporter.BaseItemExporter(fields_to_export=None, export_empty_fields=False, encoding='utf-8')

This is the (abstract) base class for all Item Exporters. It provides support for common features used by all (concrete) Item Exporters, such as defining what fields to export, whether to export empty fields, or which encoding to use.

These features can be configured through the constructor arguments which populate their respective instance attributes: fields_to_export, export_empty_fields, encoding.

export_item(item)

Exports the given item. This method must be implemented in subclasses.

serialize_field(field, name, value)

Return the serialized value for the given field. You can override this method (in your custom Item Exporters) if you want to control how a particular field or value will be serialized/exported.

By default, this method looks for a serializer declared in the item field and returns the result of applying that serializer to the value. If no serializer is found, it returns the value unchanged except for unicode values which are encoded to str using the encoding declared in the encoding attribute.

Parameters:
  • field (Field object) – the field being serialized
  • name (str) – the name of the field being serialized
  • value – the value being serialized
start_exporting()

Signal the beginning of the exporting process. Some exporters may use this to generate some required header (for example, the XmlItemExporter). You must call this method before exporting any items.

finish_exporting()

Signal the end of the exporting process. Some exporters may use this to generate some required footer (for example, the XmlItemExporter). You must always call this method after you have no more items to export.

fields_to_export

A list with the name of the fields that will be exported, or None if you want to export all fields. Defaults to None.

Some exporters (like CsvItemExporter) respect the order of the fields defined in this attribute.

export_empty_fields

Whether to include empty/unpopulated item fields in the exported data. Defaults to False. Some exporters (like CsvItemExporter) ignore this attribute and always export all empty fields.

encoding

The encoding that will be used to encode unicode values. This only affects unicode values (which are always serialized to str using this encoding). Other value types are passed unchanged to the specific serialization library.

XmlItemExporter

class scrapy.contrib.exporter.XmlItemExporter(file, item_element='item', root_element='items', **kwargs)

Exports Items in XML format to the specified file object.

Parameters:
  • file – the file-like object to use for exporting the data.
  • root_element (str) – The name of root element in the exported XML.
  • item_element (str) – The name of each item element in the exported XML.

The additional keyword arguments of this constructor are passed to the BaseItemExporter constructor.

A typical output of this exporter would be:

<?xml version="1.0" encoding="utf-8"?>
<items>
  <item>
    <name>Color TV</name>
    <price>1200</price>
 </item>
  <item>
    <name>DVD player</name>
    <price>200</price>
 </item>
</items>

Unless overridden in the serialize_field() method, multi-valued fields are exported by serializing each value inside a <value> element. This is for convenience, as multi-valued fields are very common.

For example, the item:

Item(name=['John', 'Doe'], age='23')

Would be serialized as:

<?xml version="1.0" encoding="utf-8"?>
<items>
  <item>
    <name>
      <value>John</value>
      <value>Doe</value>
    </name>
    <age>23</age>
  </item>
</items>

CsvItemExporter

class scrapy.contrib.exporter.CsvItemExporter(file, include_headers_line=True, join_multivalued=', ', **kwargs)

Exports Items in CSV format to the given file-like object. If the fields_to_export attribute is set, it will be used to define the CSV columns and their order. The export_empty_fields attribute has no effect on this exporter.

Parameters:
  • file – the file-like object to use for exporting the data.
  • include_headers_line (str) – If enabled, makes the exporter output a header line with the field names taken from BaseItemExporter.fields_to_export or the first exported item fields.
  • join_multivalued – The char (or chars) that will be used for joining multi-valued fields, if found.

The additional keyword arguments of this constructor are passed to the BaseItemExporter constructor, and the leftover arguments to the csv.writer constructor, so you can use any csv.writer constructor argument to customize this exporter.

A typical output of this exporter would be:

product,price
Color TV,1200
DVD player,200

PickleItemExporter

class scrapy.contrib.exporter.PickleItemExporter(file, protocol=0, **kwargs)

Exports Items in pickle format to the given file-like object.

Parameters:
  • file – the file-like object to use for exporting the data.
  • protocol (int) – The pickle protocol to use.

For more information, refer to the pickle module documentation.

The additional keyword arguments of this constructor are passed to the BaseItemExporter constructor.

Pickle isn’t a human readable format, so no output examples are provided.

PprintItemExporter

class scrapy.contrib.exporter.PprintItemExporter(file, **kwargs)

Exports Items in pretty print format to the specified file object.

Parameters:file – the file-like object to use for exporting the data.

The additional keyword arguments of this constructor are passed to the BaseItemExporter constructor.

A typical output of this exporter would be:

{'name': 'Color TV', 'price': '1200'}
{'name': 'DVD player', 'price': '200'}

Longer lines (when present) are pretty-formatted.

JsonItemExporter

class scrapy.contrib.exporter.JsonItemExporter(file, **kwargs)

Exports Items in JSON format to the specified file-like object, writing all objects as a list of objects. The additional constructor arguments are passed to the BaseItemExporter constructor, and the leftover arguments to the JSONEncoder constructor, so you can use any JSONEncoder constructor argument to customize this exporter.

Parameters:file – the file-like object to use for exporting the data.

A typical output of this exporter would be:

[{"name": "Color TV", "price": "1200"},
{"name": "DVD player", "price": "200"}]

Warning

JSON is very simple and flexible serialization format, but it doesn’t scale well for large amounts of data since incremental (aka. stream-mode) parsing is not well supported (if at all) among JSON parsers (on any language), and most of them just parse the entire object in memory. If you want the power and simplicity of JSON with a more stream-friendly format, consider using JsonLinesItemExporter instead, or splitting the output in multiple chunks.

JsonLinesItemExporter

class scrapy.contrib.exporter.JsonLinesItemExporter(file, **kwargs)

Exports Items in JSON format to the specified file-like object, writing one JSON-encoded item per line. The additional constructor arguments are passed to the BaseItemExporter constructor, and the leftover arguments to the JSONEncoder constructor, so you can use any JSONEncoder constructor argument to customize this exporter.

Parameters:file – the file-like object to use for exporting the data.

A typical output of this exporter would be:

{"name": "Color TV", "price": "1200"}
{"name": "DVD player", "price": "200"}

Unlike the one produced by JsonItemExporter, the format produced by this exporter is well suited for serializing large amounts of data.