from abc import abstractmethod, ABCMeta
from collections import deque
from collections.abc import KeysView, MutableMapping
from types import MappingProxyType
from typing import Any, Iterator
from itemadapter.utils import (
is_attrs_instance,
is_dataclass_instance,
is_item,
is_scrapy_item,
)
__all__ = [
"AdapterInterface",
"AttrsAdapter",
"DataclassAdapter",
"DictAdapter",
"ItemAdapter",
"ScrapyItemAdapter",
]
class AdapterInterface(MutableMapping, metaclass=ABCMeta):
"""
Abstract Base Class for adapters.
An adapter that handles a specific type of item should inherit from this
class and implement the abstract methods defined here, plus the
abtract methods inherited from the MutableMapping base class.
"""
def __init__(self, item: Any) -> None:
self.item = item
@classmethod
@abstractmethod
def is_item(cls, item: Any) -> bool:
"""
Return True if the adapter can handle the given item, False otherwise
"""
raise NotImplementedError()
def get_field_meta(self, field_name: str) -> MappingProxyType:
"""
Return metadata for the given field name, if available
"""
return MappingProxyType({})
def field_names(self) -> KeysView:
"""
Return a dynamic view of the item's field names
"""
return self.keys() # type: ignore
class _MixinAttrsDataclassAdapter:
_fields_dict: dict
item: Any
def get_field_meta(self, field_name: str) -> MappingProxyType:
return self._fields_dict[field_name].metadata # type: ignore
def field_names(self) -> KeysView:
return KeysView(self._fields_dict)
def __getitem__(self, field_name: str) -> Any:
if field_name in self._fields_dict:
return getattr(self.item, field_name)
raise KeyError(field_name)
def __setitem__(self, field_name: str, value: Any) -> None:
if field_name in self._fields_dict:
setattr(self.item, field_name, value)
else:
raise KeyError(f"{self.item.__class__.__name__} does not support field: {field_name}")
def __delitem__(self, field_name: str) -> None:
if field_name in self._fields_dict:
try:
delattr(self.item, field_name)
except AttributeError:
raise KeyError(field_name)
else:
raise KeyError(f"{self.item.__class__.__name__} does not support field: {field_name}")
def __iter__(self) -> Iterator:
return iter(attr for attr in self._fields_dict if hasattr(self.item, attr))
def __len__(self) -> int:
return len(list(iter(self)))
class AttrsAdapter(_MixinAttrsDataclassAdapter, AdapterInterface):
def __init__(self, item: Any) -> None:
super().__init__(item)
import attr
# store a reference to the item's fields to avoid O(n) lookups and O(n^2) traversals
self._fields_dict = attr.fields_dict(self.item.__class__)
@classmethod
def is_item(cls, item: Any) -> bool:
return is_attrs_instance(item)
class DataclassAdapter(_MixinAttrsDataclassAdapter, AdapterInterface):
def __init__(self, item: Any) -> None:
super().__init__(item)
import dataclasses
# store a reference to the item's fields to avoid O(n) lookups and O(n^2) traversals
self._fields_dict = {field.name: field for field in dataclasses.fields(self.item)}
@classmethod
def is_item(cls, item: Any) -> bool:
return is_dataclass_instance(item)
class _MixinDictScrapyItemAdapter:
_fields_dict: dict
item: Any
def __getitem__(self, field_name: str) -> Any:
return self.item[field_name]
def __setitem__(self, field_name: str, value: Any) -> None:
self.item[field_name] = value
def __delitem__(self, field_name: str) -> None:
del self.item[field_name]
def __iter__(self) -> Iterator:
return iter(self.item)
def __len__(self) -> int:
return len(self.item)
class DictAdapter(_MixinDictScrapyItemAdapter, AdapterInterface):
@classmethod
def is_item(cls, item: Any) -> bool:
return isinstance(item, dict)
def get_field_meta(self, field_name: str) -> MappingProxyType:
return MappingProxyType({})
def field_names(self) -> KeysView:
return KeysView(self.item)
class ScrapyItemAdapter(_MixinDictScrapyItemAdapter, AdapterInterface):
@classmethod
def is_item(cls, item: Any) -> bool:
return is_scrapy_item(item)
def get_field_meta(self, field_name: str) -> MappingProxyType:
return MappingProxyType(self.item.fields[field_name])
def field_names(self) -> KeysView:
return KeysView(self.item.fields)
[docs]class ItemAdapter(MutableMapping):
"""
Wrapper class to interact with data container objects. It provides a common interface
to extract and set data without having to take the object's type into account.
"""
ADAPTER_CLASSES = deque(
[
ScrapyItemAdapter,
DictAdapter,
DataclassAdapter,
AttrsAdapter,
]
)
def __init__(self, item: Any) -> None:
self.adapter_class = None
for cls in self.ADAPTER_CLASSES:
if cls.is_item(item):
self.adapter = cls(item) # type: ignore
break
else:
raise TypeError(f"No adapter found for objects of type: {type(item)} ({item})")
@classmethod
def is_item(self, item: Any) -> bool:
for cls in self.ADAPTER_CLASSES:
if cls.is_item(item):
return True
return False
@property
def item(self) -> Any:
return self.adapter.item
def __repr__(self) -> str:
values = ", ".join(["%s=%r" % (key, value) for key, value in self.items()])
return f"<ItemAdapter for {self.item.__class__.__name__}({values})>"
def __getitem__(self, field_name: str) -> Any:
return self.adapter.__getitem__(field_name)
def __setitem__(self, field_name: str, value: Any) -> None:
self.adapter.__setitem__(field_name, value)
def __delitem__(self, field_name: str) -> None:
self.adapter.__delitem__(field_name)
def __iter__(self) -> Iterator:
return self.adapter.__iter__()
def __len__(self) -> int:
return self.adapter.__len__()
def get_field_meta(self, field_name: str) -> MappingProxyType:
"""
Return a read-only mapping with metadata for the given field name. If there is no metadata
for the field, or the wrapped item does not support field metadata, an empty object is
returned.
Field metadata is taken from different sources, depending on the item type:
* scrapy.item.Item: corresponding scrapy.item.Field object
* dataclass items: "metadata" attribute for the corresponding field
* attrs items: "metadata" attribute for the corresponding field
The returned value is an instance of types.MappingProxyType, i.e. a dynamic read-only view
of the original mapping, which gets automatically updated if the original mapping changes.
"""
return self.adapter.get_field_meta(field_name)
def field_names(self) -> KeysView:
"""
Return read-only key view with the names of all the defined fields for the item
"""
return self.adapter.field_names()
def asdict(self) -> dict:
"""
Return a dict object with the contents of the adapter. This works slightly different than
calling `dict(adapter)`: it's applied recursively to nested items (if there are any).
"""
return {key: _asdict(value) for key, value in self.items()} # type: ignore
def _asdict(obj: Any) -> Any:
"""
Helper for ItemAdapter.asdict
"""
if isinstance(obj, dict):
return {key: _asdict(value) for key, value in obj.items()}
elif isinstance(obj, (list, set, tuple)):
return obj.__class__(_asdict(x) for x in obj)
elif isinstance(obj, ItemAdapter):
return obj.asdict()
elif is_item(obj):
return ItemAdapter(obj).asdict()
else:
return obj