"""
Item Loader
See documentation in docs/topics/loaders.rst
"""
from collections import defaultdict
from contextlib import suppress
from scrapy.item import Item
from scrapy.loader.common import wrap_loader_context
from scrapy.loader.processors import Identity
from scrapy.selector import Selector
from scrapy.utils.misc import arg_to_iter, extract_regex
from scrapy.utils.python import flatten
def unbound_method(method):
"""
Allow to use single-argument functions as input or output processors
(no need to define an unused first 'self' argument)
"""
with suppress(AttributeError):
if '.' not in method.__qualname__:
return method.__func__
return method
[docs]class ItemLoader(object):
default_item_class = Item
default_input_processor = Identity()
default_output_processor = Identity()
default_selector_class = Selector
def __init__(self, item=None, selector=None, response=None, parent=None, **context):
if selector is None and response is not None:
selector = self.default_selector_class(response)
self.selector = selector
context.update(selector=selector, response=response)
if item is None:
item = self.default_item_class()
self.context = context
self.parent = parent
self._local_item = context['item'] = item
self._local_values = defaultdict(list)
# values from initial item
for field_name, value in item.items():
self._values[field_name] += arg_to_iter(value)
@property
def _values(self):
if self.parent is not None:
return self.parent._values
else:
return self._local_values
@property
def item(self):
if self.parent is not None:
return self.parent.item
else:
return self._local_item
[docs] def nested_xpath(self, xpath, **context):
selector = self.selector.xpath(xpath)
context.update(selector=selector)
subloader = self.__class__(
item=self.item, parent=self, **context
)
return subloader
[docs] def nested_css(self, css, **context):
selector = self.selector.css(css)
context.update(selector=selector)
subloader = self.__class__(
item=self.item, parent=self, **context
)
return subloader
[docs] def add_value(self, field_name, value, *processors, **kw):
value = self.get_value(value, *processors, **kw)
if value is None:
return
if not field_name:
for k, v in value.items():
self._add_value(k, v)
else:
self._add_value(field_name, value)
[docs] def replace_value(self, field_name, value, *processors, **kw):
value = self.get_value(value, *processors, **kw)
if value is None:
return
if not field_name:
for k, v in value.items():
self._replace_value(k, v)
else:
self._replace_value(field_name, value)
def _add_value(self, field_name, value):
value = arg_to_iter(value)
processed_value = self._process_input_value(field_name, value)
if processed_value:
self._values[field_name] += arg_to_iter(processed_value)
def _replace_value(self, field_name, value):
self._values.pop(field_name, None)
self._add_value(field_name, value)
[docs] def get_value(self, value, *processors, **kw):
regex = kw.get('re', None)
if regex:
value = arg_to_iter(value)
value = flatten(extract_regex(regex, x) for x in value)
for proc in processors:
if value is None:
break
_proc = proc
proc = wrap_loader_context(proc, self.context)
try:
value = proc(value)
except Exception as e:
raise ValueError("Error with processor %s value=%r error='%s: %s'" %
(_proc.__class__.__name__, value,
type(e).__name__, str(e)))
return value
[docs] def load_item(self):
item = self.item
for field_name in tuple(self._values):
value = self.get_output_value(field_name)
if value is not None:
item[field_name] = value
return item
[docs] def get_output_value(self, field_name):
proc = self.get_output_processor(field_name)
proc = wrap_loader_context(proc, self.context)
try:
return proc(self._values[field_name])
except Exception as e:
raise ValueError("Error with output processor: field=%r value=%r error='%s: %s'" %
(field_name, self._values[field_name], type(e).__name__, str(e)))
[docs] def get_collected_values(self, field_name):
return self._values[field_name]
[docs] def get_output_processor(self, field_name):
proc = getattr(self, '%s_out' % field_name, None)
if not proc:
proc = self._get_item_field_attr(field_name, 'output_processor',
self.default_output_processor)
return unbound_method(proc)
def _process_input_value(self, field_name, value):
proc = self.get_input_processor(field_name)
_proc = proc
proc = wrap_loader_context(proc, self.context)
try:
return proc(value)
except Exception as e:
raise ValueError(
"Error with input processor %s: field=%r value=%r "
"error='%s: %s'" % (_proc.__class__.__name__, field_name,
value, type(e).__name__, str(e)))
def _get_item_field_attr(self, field_name, key, default=None):
if isinstance(self.item, Item):
value = self.item.fields[field_name].get(key, default)
else:
value = default
return value
def _check_selector_method(self):
if self.selector is None:
raise RuntimeError("To use XPath or CSS selectors, "
"%s must be instantiated with a selector "
"or a response" % self.__class__.__name__)
[docs] def add_xpath(self, field_name, xpath, *processors, **kw):
values = self._get_xpathvalues(xpath, **kw)
self.add_value(field_name, values, *processors, **kw)
[docs] def replace_xpath(self, field_name, xpath, *processors, **kw):
values = self._get_xpathvalues(xpath, **kw)
self.replace_value(field_name, values, *processors, **kw)
[docs] def get_xpath(self, xpath, *processors, **kw):
values = self._get_xpathvalues(xpath, **kw)
return self.get_value(values, *processors, **kw)
def _get_xpathvalues(self, xpaths, **kw):
self._check_selector_method()
xpaths = arg_to_iter(xpaths)
return flatten(self.selector.xpath(xpath).getall() for xpath in xpaths)
[docs] def add_css(self, field_name, css, *processors, **kw):
values = self._get_cssvalues(css, **kw)
self.add_value(field_name, values, *processors, **kw)
[docs] def replace_css(self, field_name, css, *processors, **kw):
values = self._get_cssvalues(css, **kw)
self.replace_value(field_name, values, *processors, **kw)
[docs] def get_css(self, css, *processors, **kw):
values = self._get_cssvalues(css, **kw)
return self.get_value(values, *processors, **kw)
def _get_cssvalues(self, csss, **kw):
self._check_selector_method()
csss = arg_to_iter(csss)
return flatten(self.selector.css(css).getall() for css in csss)