"""
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 typing import Dict
from scrapy.utils.trackref import object_ref
class Field(dict):
"""Container of field metadata"""
class Item(MutableMapping, object_ref, 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.
"""
fields: Dict[str, Field]
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(f"{self.__class__.__name__} does not support field: {key}")
def __delitem__(self, key):
del self._values[key]
def __getattr__(self, name):
if name in self.fields:
raise AttributeError(f"Use item[{name!r}] to get field value")
raise AttributeError(name)
def __setattr__(self, name, value):
if not name.startswith("_"):
raise AttributeError(f"Use item[{name!r}] = {value!r} to set field value")
super().__setattr__(name, value)
def __len__(self):
return len(self._values)
def __iter__(self):
return iter(self._values)
__hash__ = object_ref.__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)