.. module:: scrapy.exporters
:synopsis: 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.
If you are in a hurry, and just want to use an Item Exporter to output scraped data see the :ref:`topics-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 :ref:`topics-exporters-reference`. After you have instantiated your exporter, you have to:
1. call the method :meth:`~BaseItemExporter.start_exporting` in order to signal the beginning of the exporting process
2. call the :meth:`~BaseItemExporter.export_item` method for each item you want to export
3. and finally call the :meth:`~BaseItemExporter.finish_exporting` to signal the end of the exporting process
Here you can see an :doc:`Item Pipeline <item-pipeline>` which uses an Item Exporter to export scraped items to different files, one per spider:
from scrapy import signals
from scrapy.exporters 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
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.
If you use :class:`~.Item` you can declare a serializer in the :ref:`field metadata <topics-items-fields>`. The serializer must be a callable which receives a value and returns its serialized form.
Example:
import scrapy
def serialize_price(value):
return '$ %s' % str(value)
class Product(scrapy.Item):
name = scrapy.Field()
price = scrapy.Field(serializer=serialize_price)
You can also override the :meth:`~BaseItemExporter.serialize_field()` method to customize how your field value will be exported.
Make sure you call the base class :meth:`~BaseItemExporter.serialize_field()` method after your custom code.
Example:
from scrapy.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)
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')
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: :attr:`fields_to_export`, :attr:`export_empty_fields`, :attr:`encoding`.
.. method:: export_item(item)
Exports the given item. This method must be implemented in subclasses.
.. method:: 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 :ref:`declared in the item
field <topics-exporters-serializers>` 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 :attr:`encoding` attribute.
:param field: the field being serialized. If a raw dict is being
exported (not :class:`~.Item`) *field* value is an empty dict.
:type field: :class:`~scrapy.item.Field` object or an empty dict
:param name: the name of the field being serialized
:type name: str
:param value: the value being serialized
.. method:: start_exporting()
Signal the beginning of the exporting process. Some exporters may use
this to generate some required header (for example, the
:class:`XmlItemExporter`). You must call this method before exporting any
items.
.. method:: finish_exporting()
Signal the end of the exporting process. Some exporters may use this to
generate some required footer (for example, the
:class:`XmlItemExporter`). You must always call this method after you
have no more items to export.
.. attribute:: 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 :class:`CsvItemExporter`) respect the order of the
fields defined in this attribute.
Some exporters may require fields_to_export list in order to export the
data properly when spiders return dicts (not :class:`~Item` instances).
.. attribute:: export_empty_fields
Whether to include empty/unpopulated item fields in the exported data.
Defaults to ``False``. Some exporters (like :class:`CsvItemExporter`)
ignore this attribute and always export all empty fields.
This option is ignored for dict items.
.. attribute:: 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.
Exports Items in XML format to the specified file object.
| param file: | the file-like object to use for exporting the data. |
|---|---|
| param root_element: | The name of root element in the exported XML. |
| type root_element: | str |
| param item_element: | The name of each item element in the exported XML. |
| type item_element: | str |
The additional keyword arguments of this constructor are passed to the :class:`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 :meth:`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>
Exports Items in CSV format to the given file-like object. If the :attr:`fields_to_export` attribute is set, it will be used to define the CSV columns and their order. The :attr:`export_empty_fields` attribute has no effect on this exporter.
| param file: | the file-like object to use for exporting the data. |
|---|---|
| param include_headers_line: | If enabled, makes the exporter output a header line with the field names taken from :attr:`BaseItemExporter.fields_to_export` or the first exported item fields. |
| type include_headers_line: | boolean |
| param join_multivalued: | The char (or chars) that will be used for joining multi-valued fields, if found. |
| type include_headers_line: | str |
The additional keyword arguments of this constructor are passed to the :class:`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
Exports Items in pickle format to the given file-like object.
| param file: | the file-like object to use for exporting the data. |
|---|---|
| param protocol: | The pickle protocol to use. |
| type protocol: | int |
For more information, refer to the pickle module documentation.
The additional keyword arguments of this constructor are passed to the :class:`BaseItemExporter` constructor.
Pickle isn't a human readable format, so no output examples are provided.
Exports Items in pretty print format to the specified file object.
| param file: | the file-like object to use for exporting the data. |
|---|
The additional keyword arguments of this constructor are passed to the :class:`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.
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 :class:`BaseItemExporter` constructor, and the leftover arguments to the JSONEncoder constructor, so you can use any JSONEncoder constructor argument to customize this exporter.
| param 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 :class:`JsonLinesItemExporter` instead, or splitting the output in multiple chunks.
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 :class:`BaseItemExporter` constructor, and the leftover arguments to the JSONEncoder constructor, so you can use any JSONEncoder constructor argument to customize this exporter.
| param 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 :class:`JsonItemExporter`, the format produced by this exporter is well suited for serializing large amounts of data.