/
item.py
135 lines (102 loc) · 4.17 KB
/
item.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
"""
Scrapy Item
See documentation in docs/topics/item.rst
"""
from __future__ import annotations
from abc import ABCMeta
from copy import deepcopy
from pprint import pformat
from typing import (
TYPE_CHECKING,
Any,
Dict,
Iterator,
KeysView,
MutableMapping,
NoReturn,
Tuple,
)
from scrapy.utils.trackref import object_ref
if TYPE_CHECKING:
# typing.Self requires Python 3.11
from typing_extensions import Self
class Field(dict):
"""Container of field metadata"""
class ItemMeta(ABCMeta):
"""Metaclass_ of :class:`Item` that handles field definitions.
.. _metaclass: https://realpython.com/python-metaclasses
"""
def __new__(
mcs, class_name: str, bases: Tuple[type, ...], attrs: Dict[str, Any]
) -> ItemMeta:
classcell = attrs.pop("__classcell__", None)
new_bases = tuple(base._class for base in bases if hasattr(base, "_class"))
_class = super().__new__(mcs, "x_" + class_name, new_bases, attrs)
fields = getattr(_class, "fields", {})
new_attrs = {}
for n in dir(_class):
v = getattr(_class, n)
if isinstance(v, Field):
fields[n] = v
elif n in attrs:
new_attrs[n] = attrs[n]
new_attrs["fields"] = fields
new_attrs["_class"] = _class
if classcell is not None:
new_attrs["__classcell__"] = classcell
return super().__new__(mcs, class_name, bases, new_attrs)
class Item(MutableMapping[str, Any], 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: Any, **kwargs: Any):
self._values: Dict[str, Any] = {}
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: str) -> Any:
return self._values[key]
def __setitem__(self, key: str, value: Any) -> None:
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: str) -> None:
del self._values[key]
def __getattr__(self, name: str) -> NoReturn:
if name in self.fields:
raise AttributeError(f"Use item[{name!r}] to get field value")
raise AttributeError(name)
def __setattr__(self, name: str, value: Any) -> None:
if not name.startswith("_"):
raise AttributeError(f"Use item[{name!r}] = {value!r} to set field value")
super().__setattr__(name, value)
def __len__(self) -> int:
return len(self._values)
def __iter__(self) -> Iterator[str]:
return iter(self._values)
__hash__ = object_ref.__hash__
def keys(self) -> KeysView[str]:
return self._values.keys()
def __repr__(self) -> str:
return pformat(dict(self))
def copy(self) -> Self:
return self.__class__(self)
def deepcopy(self) -> Self:
"""Return a :func:`~copy.deepcopy` of this item."""
return deepcopy(self)