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"""The Constant extractor produces pre-specified triples.
Part of the bsie module.
A copy of the license is provided with the project.
Author: Matthias Baumgartner, 2022
"""
# imports
import typing
# bsie imports
from bsie.base import extractor
from bsie.utils.bsfs import URI, schema as _schema
from bsie.utils.node import Node
# exports
__all__: typing.Sequence[str] = (
'Constant',
)
## code ##
class Constant(extractor.Extractor):
"""Extract information from file's path."""
CONTENT_READER = None
# predicate/value pairs to be produced.
_tuples: typing.Tuple[typing.Tuple[_schema.Predicate, typing.Any], ...]
def __init__(
self,
schema: str,
tuples: typing.Iterable[typing.Tuple[URI, typing.Any]],
):
super().__init__(_schema.Schema.from_string(extractor.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)
# FIXME: use schema instance for value checking
def extract(
self,
subject: Node,
content: None,
predicates: typing.Iterable[_schema.Predicate],
) -> typing.Iterator[typing.Tuple[Node, _schema.Predicate, typing.Any]]:
for pred, value in self._tuples:
if pred in predicates:
yield subject, pred, value
## EOF ##
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