1 files changed, 57 insertions, 0 deletions
diff --git a/bsie/extractor/generic/constant.py b/bsie/extractor/generic/constant.py
new file mode 100644
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+++ b/bsie/extractor/generic/constant.py
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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 import bsfs, 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[bsfs.schema.Predicate, typing.Any], ...]
+
+    def __init__(
+            self,
+            schema: str,
+            tuples: typing.Iterable[typing.Tuple[bsfs.URI, typing.Any]],
+            ):
+        super().__init__(bsfs.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)
+        # 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 ##