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"""The Constant extractor produces pre-specified triples.
"""
# standard imports
import typing
# bsie imports
from bsie.utils import bsfs, node
# inner-module imports
from .. import base
# exports
__all__: typing.Sequence[str] = (
'Constant',
)
## code ##
class Constant(base.Extractor):
"""Extract information from file's path."""
CONTENT_READER = None
# predicate/value pairs to be produced.
_tuples: typing.Tuple[typing.Tuple[bsfs.schema.Predicate, typing.Any], ...]
def __init__(
self,
schema: str,
tuples: typing.Iterable[typing.Tuple[bsfs.URI, typing.Any]],
):
super().__init__(bsfs.schema.from_string(base.SCHEMA_PREAMBLE + schema))
# NOTE: Raises a KeyError if the predicate is not part of the schema
self._tuples = tuple((self.schema.predicate(p_uri), value) for p_uri, value in tuples)
# TODO: use schema instance for value checking
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) \
and self._tuples == other._tuples
def __hash__(self) -> int:
return hash((super().__hash__(), self._tuples))
def extract(
self,
subject: node.Node,
content: None,
principals: typing.Iterable[bsfs.schema.Predicate],
) -> typing.Iterator[typing.Tuple[node.Node, bsfs.schema.Predicate, typing.Any]]:
for pred, value in self._tuples:
if pred in principals:
yield subject, pred, value
## EOF ##
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