"""
Scrapy Item
See documentation in docs/topics/item.rst
"""
from abc import ABCMeta
from collections.abc import MutableMapping
from copy import deepcopy
from pprint import pformat
from warnings import warn
from scrapy.utils.deprecate import ScrapyDeprecationWarning
from scrapy.utils.trackref import object_ref
class _BaseItem(object_ref):
"""
Temporary class used internally to avoid the deprecation
warning raised by isinstance checks using BaseItem.
"""
pass
class _BaseItemMeta(ABCMeta):
def __instancecheck__(cls, instance):
if cls is BaseItem:
warn('scrapy.item.BaseItem is deprecated, please use scrapy.item.Item instead',
ScrapyDeprecationWarning, stacklevel=2)
return super().__instancecheck__(instance)
class BaseItem(_BaseItem, metaclass=_BaseItemMeta):
"""
Deprecated, please use :class:`scrapy.item.Item` instead
"""
def __new__(cls, *args, **kwargs):
if issubclass(cls, BaseItem) and not issubclass(cls, (Item, DictItem)):
warn('scrapy.item.BaseItem is deprecated, please use scrapy.item.Item instead',
ScrapyDeprecationWarning, stacklevel=2)
return super(BaseItem, cls).__new__(cls, *args, **kwargs)
[docs]class Field(dict):
"""Container of field metadata"""
class DictItem(MutableMapping, BaseItem):
fields = {}
def __new__(cls, *args, **kwargs):
if issubclass(cls, DictItem) and not issubclass(cls, Item):
warn('scrapy.item.DictItem is deprecated, please use scrapy.item.Item instead',
ScrapyDeprecationWarning, stacklevel=2)
return super(DictItem, cls).__new__(cls, *args, **kwargs)
def __init__(self, *args, **kwargs):
self._values = {}
if args or kwargs: # avoid creating dict for most common case
for k, v in dict(*args, **kwargs).items():
self[k] = v
def __getitem__(self, key):
return self._values[key]
def __setitem__(self, key, value):
if key in self.fields:
self._values[key] = value
else:
raise KeyError("%s does not support field: %s" % (self.__class__.__name__, key))
def __delitem__(self, key):
del self._values[key]
def __getattr__(self, name):
if name in self.fields:
raise AttributeError("Use item[%r] to get field value" % name)
raise AttributeError(name)
def __setattr__(self, name, value):
if not name.startswith('_'):
raise AttributeError("Use item[%r] = %r to set field value" % (name, value))
super(DictItem, self).__setattr__(name, value)
def __len__(self):
return len(self._values)
def __iter__(self):
return iter(self._values)
__hash__ = BaseItem.__hash__
def keys(self):
return self._values.keys()
def __repr__(self):
return pformat(dict(self))
def copy(self):
return self.__class__(self)
def deepcopy(self):
"""Return a :func:`~copy.deepcopy` of this item.
"""
return deepcopy(self)
[docs]class Item(DictItem, metaclass=ItemMeta):
"""
Base class for scraped items.
In Scrapy, an object is considered an ``item`` if it is an instance of either
:class:`Item` or :class:`dict`, or any subclass. For example, when the output of a
spider callback is evaluated, only instances of :class:`Item` or
:class:`dict` are passed to :ref:`item pipelines <topics-item-pipeline>`.
If you need instances of a custom class to be considered items by Scrapy,
you must inherit from either :class:`Item` or :class:`dict`.
Items must declare :class:`Field` attributes, which are processed and stored
in the ``fields`` attribute. This restricts the set of allowed field names
and prevents typos, raising ``KeyError`` when referring to undefined fields.
Additionally, fields can be used to define metadata and control the way
data is processed internally. Please refer to the :ref:`documentation
about fields <topics-items-fields>` for additional information.
Unlike instances of :class:`dict`, instances of :class:`Item` may be
:ref:`tracked <topics-leaks-trackrefs>` to debug memory leaks.
"""