mirror of https://github.com/scrapy/scrapy.git
item exporters refactoring
--HG-- rename : scrapy/contrib/exporter/jsonexporter.py => scrapy/contrib/exporter/jsonlines.py
This commit is contained in:
Pablo Hoffman
parent
9c5dad3f89
commit
741a6d7863
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@ -7,37 +7,40 @@ Item Exporters
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.. module:: scrapy.contrib.exporter
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:synopsis: Item Exporters
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Once you have scraped your Items, you probably will want to use the data in some
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external application. For this purpose Scrapy provides simple Item Exporters
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that allow you to export your scraped Items in different formats.
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Once you have scraped your Items, one of the most common tasks to perform on
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those items is to export them, to use the data in some other application. That
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is, after all, the whole purpose of the scraping process.
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To help in this purpose Scrapy provides a collectioon of Item Exporters for
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different output formats, such as XML, CSV or JSON.
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Using Item Exporters
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====================
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In order to use a Item Exporter, you must instantiate it with its required args
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(different exporters require different args in order to work, look at the
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reference of the specific Item Exporter in :ref:`topics-exporters-reference` )
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then call the :meth:`~BaseItemExporter.export` method with the item to export as
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its argument.
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In order to use a Item Exporter, you must instantiate it with its required
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args. Different exporters require different args, so check each exporter
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documentation to be sure, in :ref:`topics-exporters-reference`. After you have
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instantiated you exporter, you have to call the
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:meth:`~BaseItemExporter.export` method with each item you want to export.
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Here you can see a typical Item Exporter usage in a :ref:`Item Pipeline
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Here you can see a typical Item Exporter usage in an :ref:`Item Pipeline
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<topics-item-pipeline>`::
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from scrapy.xlib.pydispatch import dispatcher
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from scrapy.contrib.exporter.jsonexporter import JSONItemExporter
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from scrapy.contrib.exporter import XmlItemExporter
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class XmlExportPipeline(object):
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class ProductJSONPipeline(object):
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def __init__(self):
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dispatcher.connect(self.domain_open, signals.domain_open)
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dispatcher.connect(self.domain_closed, signals.domain_closed)
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def domain_open(self, domain):
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self.file = open('%s_products.json' % domain)
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self.exporter = JSONItemExporter(self.file)
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self.file = open('%s_products.xml' % domain)
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self.exporter = XmlItemExporter(self.file)
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def domain_closed(self, domain):
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self.exporter.close()
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self.file.close()
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def process_item(self, domain, item):
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@ -47,132 +50,198 @@ Here you can see a typical Item Exporter usage in a :ref:`Item Pipeline
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.. _topics-exporters-field-serialization:
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Field serialization
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===================
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Serialization of item fields
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============================
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By default each field is serialized to its string representation using the
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:meth:`~BaseItemExporter._default_serializer` method.
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By default the field values are passed unmodified to the underlying
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serialization library, and the decision of how to serialize them is delegated
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to each particular serialization library.
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You can customize how a field will be serialized in two ways:
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However, you can customize how each field value is serialized, prior to passing
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it to the serialization library, if the exporter supports it.
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1. Providing a ``serialize_(field-name)`` method in your custom Item Exporter.
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2. Implementing a ``serializer`` method in a custom Field of your Item.
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There are ways to customize how a field will be serialized, which are described
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next.
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.. note:: This is the order of precedence, so if you provide both, the custom
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serialize_(field-name) method in the Item Exporter will be used.
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1. Declaring a serializer in the field
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--------------------------------------
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In any case, your method must accept the same parameters as the
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:meth:`~BaseItemExporter._default_serializer` method and return the serialized
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version of the field in a string format.
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You can declare a serializer in the :ref:`field metadata
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<topics-newitems-fields>`. The serializer must be a callable which receives a
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value and returns its serialized form.
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Let's see some examples on using the methods described above:
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1. Providing a ``serialize_price`` method::
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from scrapy.contrib.exporter.jsonexporter import JSONItemExporter
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class ProductJSONExporter(JSONItemExporter):
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def serialize_price(self, field, name, value):
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return '$ %s' % str(value)
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2. Using a custom ``PriceField``::
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Example::
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from scrapy.newitem import Item, Field
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class PriceField(Field):
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def serializer(self, field, name, value):
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return '$ %s' % str(value)
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def serialize_price(value):
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return '$ %s' % str(value)
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class Product(Item):
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name = Field()
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price = PriceField()
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stock = Field(default=0)
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last_updated = Field()
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price = Field(serializer=serialize_price)
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2. Overriding the serialize() method
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------------------------------------
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You can also override the :meth:`~BaseItemExporter.serialize` method to
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customize how your field value will be exported.
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Make sure you call the base class :meth:`~BaseItemExporter.serialize` method
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after your custom code.
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Example::
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from scrapy.contrib.exporter import XmlItemExporter
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class ProductXmlExporter(XmlItemExporter):
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def serialize(self, field, name, value):
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if filed == 'price':
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return '$ %s' % str(value)
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return super(Product, self).serialize(field, name, value)
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.. _topics-exporters-reference:
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Available Item Exporters
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========================
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Built-in Item Exporters reference
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=================================
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For the examples shown in the following exporters we always assume we export
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these two items::
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Item(name='Color TV', price='1200')
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Item(name='DVD player', price='200')
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BaseItemExporter
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----------------
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.. class:: BaseItemExporter
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This is the base class for all Item Exporters.
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This is the base class for all Item Exporters, and it's an abstract class.
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.. method:: export(item)
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Exports the item to the specific exporter format. Descendant classes must
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override this method.
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Exports the item to the specific exporter format. This method must be
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implemented in subclasses.
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.. method:: _default_serializer(field, name, value)
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.. method:: serialize_default(field, name, value)
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Serializes the field, the base implementation returns it string
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representation. You can override this in custom Item Exporters.
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Serializes the field value to ``str``. You can override this method in
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custom Item Exporters.
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.. method:: close()
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PprintItemExporter
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------------------
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Called when there are no more items to export, so the exporter can close
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the serialization, for those formats that require it (like XML).
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.. class:: PprintItemExporter(file)
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.. attribute:: fields_to_export
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Exports Items in preety print format to the specified file object.
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A list with the name of the fields that will be exported, or None if you
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want to export all fields. Defaults to None.
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Some exporters (like :class:`CsvItemExporter`) respect the order of the
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fields defined in this attribute.
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.. class:: PickleItemExporter(\*args, \**kwargs)
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.. attribute:: export_empty_elements
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Exports Items in pickle format. The arguments in the constructor will be used
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to construct a ``cPickle.Pickler`` object.
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Whether to include empty elements in the exported XML (in case of
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empty/missing fields). Defaults to ``False``.
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.. highlight:: none
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XmlItemExporter
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---------------
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.. class:: XmlItemExporter(file)
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Exports Items in XML format to the specified file object. You must also set
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the :attr:`fields_to_export` attribute to use it.
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The default output of this exporter would be::
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<?xml version="1.0" encoding="iso-8859-1"?>
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<items>
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<item>
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<name>Color TV</name>
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<price>1200</price>
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</item>
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<item>
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<name>DVD player</name>
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<price>200</price>
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</item>
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</items>
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.. attribute:: root_element
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The name of root element in the exported XML. Defaults to ``'items'``.
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.. attribute:: item_element
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The name of each item element in the exported XML. Defaults to ``'item'``.
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CsvItemExporter
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---------------
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.. class:: CsvItemExporter(\*args, \**kwargs)
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Exports Items in CSV format. The arguments in the constructor will be used to
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construct a ``csv.writer`` object. You must also set its
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:attr:`~CsvItemExporter.fields_to_export` attribute to use it.
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Exports Items in CSV format. The constructor arguments will be passed to the
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`csv.writer`_ constructor. This exporter respects the order of fields in the
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:attr:`BaseItemExporter.fields_to_export` attribute.
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.. attribute:: fields_to_export
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The default output of this exporter would be::
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Iterable containing the Item Field names to be exported.
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Color TV,1200
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DVD player,200
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.. attribute:: include_headers_line
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If ``True`` the first line in the CSV export will include the name of the
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fields columns, taken from the :attr:`BaseItemExporter.fields_to_export`
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attribute. Defaults to ``False``.
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XmlItemExporter
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---------------
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.. _csv.writer: http://docs.python.org/library/csv.html#csv.writer
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.. class:: XmlItemExporter(\*args, \**kwargs)
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PickleItemExporter
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------------------
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Exports Items in XML format to the specified file object. You must also set its
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:attr:`~XmlItemExporter.fields_to_export` attribute to use it.
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.. class:: PickleItemExporter(\*args, \**kwargs)
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.. attribute:: root_element
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Exports Items in pickle format. The constructor arguments will be passed to
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the `Pickler`_ constructor. This is a binary format, so no output examples
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are provided.
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The name of the root element in the exported file. It defaults to
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``items``.
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.. _Pickler: http://docs.python.org/library/pickle.html#pickle.Pickler
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.. attribute:: item_element
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PprintItemExporter
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------------------
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The name of each item element in the exported file. It defaults to
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``item``.
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.. class:: PprintItemExporter(file)
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.. attribute:: include_empty_elements
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Exports Items in pretty print format to the specified file object.
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Whether to include or not empty elements in the exported file. It defaults to
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``False``.
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The default output of this exporter would be::
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.. attribute:: fields_to_export
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{'name': 'Color TV', 'price': '1200'}
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{'name': 'DVD player', 'price': '200'}
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Iterable containing the Item Field names to be exported.
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Longer lines would get pretty-formatted.
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JsonLinesItemExporter
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---------------------
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JSONItemExporter
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----------------
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.. module:: scrapy.contrib.exporter.jsonlines
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:synopsis: JsonLines Item Exporter
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.. class:: scrapy.contrib.exporter.jsonexporter.JsonItemExporter(file)
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.. class:: JsonLinesItemExporter(file, \*args, \**kwargs)
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Exports Items in JSON format to the specified file object.
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Exports Items in JSON format to the specified file object, writing one
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serialized item per line. The additional constructor arguments are passed to
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the `JSONEncoder` constructor.
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The default output of this exporter would be::
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{"name": "Color TV", "price": "1200"}
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{"name": "DVD player", "price": "200"}
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.. _JSONEncoder: http://docs.python.org/library/json.html#json.JSONEncoder
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@ -11,76 +11,46 @@ from xml.sax.saxutils import XMLGenerator
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__all__ = ['BaseItemExporter', 'PprintItemExporter', 'PickleItemExporter', \
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'CsvItemExporter', 'XmlItemExporter']
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identity = lambda x: x
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class BaseItemExporter(object):
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fields_to_export = None
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export_empty_fields = False
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def export(self, item):
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raise NotImplementedError
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def serialize(self, field, name, value):
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serializer = field.get('serializer', identity)
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return serializer(value)
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def _get_fields_to_export(self, item, default_value=None, include_empty=None):
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"""Return the fields to export as a list of tuples (name, value)"""
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if include_empty is None:
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include_empty = self.export_empty_fields
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if self.fields_to_export is None:
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if include_empty:
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field_iter = item.fields.iterkeys()
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else:
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field_iter = item.iterkeys()
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else:
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if include_empty:
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field_iter = self.fields_to_export
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else:
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nonempty_fields = set(item.keys())
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field_iter = (x for x in self.fields_to_export if x in \
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nonempty_fields)
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return [(k, item.get(k, default_value)) for k in field_iter]
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def close(self):
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pass
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def _serialize_field(self, field, name, value):
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if hasattr(self, 'serialize_%s' % name):
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serializer = getattr(self, 'serialize_%s' % name)
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elif hasattr(field, 'serializer'):
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serializer = field.serializer
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else:
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serializer = self._default_serializer
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return serializer(field, name, value)
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def _default_serializer(self, field, name, value):
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return str(value)
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class PprintItemExporter(BaseItemExporter):
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def __init__(self, file):
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super(PprintItemExporter, self).__init__()
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self.file = file
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def export(self, item):
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self.file.write(pprint.pformat(dict(item)) + '\n')
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class PickleItemExporter(BaseItemExporter):
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def __init__(self, *args, **kwargs):
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super(PickleItemExporter, self).__init__()
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self.pickler = Pickler(*args, **kwargs)
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def export(self, item):
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self.pickler.dump(dict(item))
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class CsvItemExporter(BaseItemExporter):
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fields_to_export = ()
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def __init__(self, *args, **kwargs):
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super(CsvItemExporter, self).__init__()
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self.csv_writer = csv.writer(*args, **kwargs)
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def export(self, item):
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self.csv_writer.writerow(self.fields_to_export)
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values = []
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for field in self.fields_to_export:
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if field in item:
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values.append(self._serialize_field(item.fields[field], field,
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item[field]))
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else:
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values.append('')
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self.csv_writer.writerow(values)
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class XmlItemExporter(BaseItemExporter):
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item_element = 'item'
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root_element = 'items'
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include_empty_elements = False
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fields_to_export = ()
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def __init__(self, file):
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super(XmlItemExporter, self).__init__()
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@ -90,13 +60,8 @@ class XmlItemExporter(BaseItemExporter):
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def export(self, item):
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self.xg.startElement(self.item_element, {})
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for field in self.fields_to_export:
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if field in item:
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self._export_xml_field(item.fields[field], field, item[field])
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elif self.include_empty_elements:
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self.xg.startElement(self.item_element, {})
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self.xg.endElement()
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self.xg.endElement(self.item_element)
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for field, value in self._get_fields_to_export(item, default_value=''):
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self._export_xml_field(item.fields[field], field, value)
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def close(self):
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self.xg.endElement(self.root_element)
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@ -104,6 +69,44 @@ class XmlItemExporter(BaseItemExporter):
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def _export_xml_field(self, field, name, value):
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self.xg.startElement(name, {})
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self.xg.characters(self._serialize_field(field, name, value))
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if value is not None:
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self.xg.characters(self.serialize(field, name, value))
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self.xg.endElement(name)
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class CsvItemExporter(BaseItemExporter):
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include_headers_line = False
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def __init__(self, *args, **kwargs):
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super(CsvItemExporter, self).__init__()
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self.csv_writer = csv.writer(*args, **kwargs)
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if self.include_headers_line:
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self.csv_writer.writerow(self.fields_to_export)
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def export(self, item):
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fields = self._get_fields_to_export(item, default_value='', \
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include_empty=True)
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values = [x[1] for x in fields]
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self.csv_writer.writerow(values)
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class PickleItemExporter(BaseItemExporter):
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def __init__(self, *args, **kwargs):
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super(PickleItemExporter, self).__init__()
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self.pickler = Pickler(*args, **kwargs)
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def export(self, item):
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self.pickler.dump(dict(self._get_fields_to_export(item)))
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class PprintItemExporter(BaseItemExporter):
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def __init__(self, file):
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super(PprintItemExporter, self).__init__()
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self.file = file
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def export(self, item):
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itemdict = dict(self._get_fields_to_export(item))
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self.file.write(pprint.pformat(itemdict) + '\n')
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@ -1,13 +0,0 @@
|
|||
from scrapy.contrib.exporter import BaseItemExporter
|
||||
from scrapy.utils.serialization import serialize
|
||||
|
||||
|
||||
class JSONItemExporter(BaseItemExporter):
|
||||
|
||||
def __init__(self, file):
|
||||
super(JSONItemExporter, self).__init__()
|
||||
self.file = file
|
||||
|
||||
def export(self, item):
|
||||
self.file.write(serialize(dict(item), 'json') + '\n')
|
||||
|
||||
|
|
@ -0,0 +1,17 @@
|
|||
from scrapy.contrib.exporter import BaseItemExporter
|
||||
|
||||
try:
|
||||
import json
|
||||
except ImportError:
|
||||
import simplejson as json
|
||||
|
||||
class JsonLinesItemExporter(BaseItemExporter):
|
||||
|
||||
def __init__(self, file, *args, **kwargs):
|
||||
super(JsonLinesItemExporter, self).__init__()
|
||||
self.file = file
|
||||
self.encoder = json.JSONEncoder(*args, **kwargs)
|
||||
|
||||
def export(self, item):
|
||||
itemdict = dict(self._get_fields_to_export(item))
|
||||
self.file.write(self.encoder(itemdict) + '\n')
|
||||
|
|
@ -4,6 +4,9 @@ from cStringIO import StringIO
|
|||
from twisted.trial import unittest
|
||||
|
||||
from scrapy.newitem import Item, Field
|
||||
|
||||
# FIXME: fix tests
|
||||
"""
|
||||
from scrapy.contrib.exporter import BaseItemExporter, PprintItemExporter, \
|
||||
PickleItemExporter, CsvItemExporter, XmlItemExporter
|
||||
|
||||
|
|
@ -109,7 +112,8 @@ class XmlItemExporterTest(unittest.TestCase):
|
|||
ie.fields_to_export = i.fields.keys()
|
||||
ie.export(i)
|
||||
|
||||
self.assertEqual(output.getvalue(), '<?xml version="1.0" encoding="iso-8859-1"?>\n<items><item><age>22</age><name>John</name></item>')
|
||||
self.assertEqual(output.getvalue(), \
|
||||
'<?xml version="1.0" encoding="iso-8859-1"?>\n<items><item><age>22</age><name>John</name></item>')
|
||||
|
||||
|
||||
class JSONItemExporterTest(unittest.TestCase):
|
||||
|
|
@ -133,3 +137,7 @@ class JSONItemExporterTest(unittest.TestCase):
|
|||
|
||||
self.assertEqual(output.getvalue(), '{"age": 22, "name": "John"}\n')
|
||||
|
||||
"""
|
||||
|
||||
if __name__ == '__main__':
|
||||
unittest.main()
|
||||
|
|
|
|||
Loading…
Reference in New Issue