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"""
Item Exporters are used to export/serialize items into different formats.
"""
import csv
import pprint
from cPickle import Pickler
from xml.sax.saxutils import XMLGenerator
__all__ = ['BaseItemExporter', 'PprintItemExporter', 'PickleItemExporter', \
'CsvItemExporter', 'XmlItemExporter']
class BaseItemExporter(object):
def __init__(self, **kwargs):
self._configure(kwargs)
def _configure(self, options, dont_fail=False):
"""Configure the exporter by poping options from the ``options`` dict.
If dont_fail is set, it won't raise an exception on unexpected options
(useful for using with keyword arguments in subclasses constructors)
"""
self.fields_to_export = options.pop('fields_to_export', None)
self.export_empty_fields = options.pop('export_empty_fields', False)
self.encoding = options.pop('encoding', 'utf-8')
if not dont_fail and options:
raise TypeError("Unexpected options: %s" % ', '.join(options.keys()))
def export_item(self, item):
raise NotImplementedError
def serialize_field(self, field, name, value):
serializer = field.get('serializer', self._to_str_if_unicode)
return serializer(value)
def start_exporting(self):
pass
def finish_exporting(self):
pass
def _to_str_if_unicode(self, value):
return value.encode(self.encoding) if isinstance(value, unicode) else value
def _get_serialized_fields(self, item, default_value=None, include_empty=None):
"""Return the fields to export as an iterable of tuples (name,
serialized_value)
"""
if include_empty is None:
include_empty = self.export_empty_fields
if self.fields_to_export is None:
if include_empty:
field_iter = item.fields.iterkeys()
else:
field_iter = item.iterkeys()
else:
if include_empty:
field_iter = self.fields_to_export
else:
nonempty_fields = set(item.keys())
field_iter = (x for x in self.fields_to_export if x in \
nonempty_fields)
for field_name in field_iter:
if field_name in item:
field = item.fields[field_name]
value = self.serialize_field(field, field_name, item[field_name])
else:
value = default_value
yield field_name, value
class XmlItemExporter(BaseItemExporter):
def __init__(self, file, **kwargs):
self.item_element = kwargs.pop('item_element', 'item')
self.root_element = kwargs.pop('root_element', 'items')
self._configure(kwargs)
self.xg = XMLGenerator(file, encoding=self.encoding)
def start_exporting(self):
self.xg.startDocument()
self.xg.startElement(self.root_element, {})
def export_item(self, item):
self.xg.startElement(self.item_element, {})
for name, value in self._get_serialized_fields(item, default_value=''):
self._export_xml_field(name, value)
self.xg.endElement(self.item_element)
def finish_exporting(self):
self.xg.endElement(self.root_element)
self.xg.endDocument()
def _export_xml_field(self, name, serialized_value):
self.xg.startElement(name, {})
if hasattr(serialized_value, '__iter__'):
for value in serialized_value:
self._export_xml_field('value', value)
else:
self.xg.characters(serialized_value)
self.xg.endElement(name)
class CsvItemExporter(BaseItemExporter):
def __init__(self, file, include_headers_line=True, **kwargs):
self._configure(kwargs, dont_fail=True)
self.include_headers_line = include_headers_line
self.csv_writer = csv.writer(file, **kwargs)
self._headers_not_written = True
def export_item(self, item):
if self._headers_not_written:
self._headers_not_written = False
self._write_headers_and_set_fields_to_export(item)
fields = self._get_serialized_fields(item, default_value='', \
include_empty=True)
values = [x[1] for x in fields]
self.csv_writer.writerow(values)
def _write_headers_and_set_fields_to_export(self, item):
if self.include_headers_line:
if not self.fields_to_export:
self.fields_to_export = item.fields.keys()
self.csv_writer.writerow(self.fields_to_export)
class PickleItemExporter(BaseItemExporter):
def __init__(self, file, protocol=0, **kwargs):
self._configure(kwargs)
self.pickler = Pickler(file, protocol)
def export_item(self, item):
self.pickler.dump(dict(self._get_serialized_fields(item)))
class PprintItemExporter(BaseItemExporter):
def __init__(self, file, **kwargs):
self._configure(kwargs)
self.file = file
def export_item(self, item):
itemdict = dict(self._get_serialized_fields(item))
self.file.write(pprint.pformat(itemdict) + '\n')
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