Add graph hashing method to utils

.pre-commit-config.yaml

@@ -20,5 +20,5 @@ repos:
     hooks:
     -   id: mypy
         args: ["--install-types", "--non-interactive", "--ignore-missing-imports", "--follow-imports=skip", "--disable-error-code=import-untyped"]
-        additional_dependencies: [sqlalchemy2-stubs <= 0.0.2a20, SQLAlchemy <= 1.4]
+        additional_dependencies: [sqlalchemy2-stubs <= 0.0.2a38, SQLAlchemy < 1.5]
 exclude: docs/conf.py

buildingmotif/utils.py

@@ -9,6 +9,7 @@
 
 import pyshacl  # type: ignore
 from rdflib import BNode, Graph, Literal, URIRef
+from rdflib.compare import _TripleCanonicalizer
 from rdflib.paths import ZeroOrOne
 from rdflib.term import Node
 
@@ -690,3 +691,22 @@ def skolemize_shapes(g: Graph) -> Graph:
     # apply the replacements
     replace_nodes(g, replacements)
     return g
+
+
+def approximate_graph_hash(graph: Graph) -> int:
+    """
+    Returns a cryptographic hash of the graph contents.
+    This uses the same method as rdflib's isomorphic function to generate a cryptographic hash of a given graph.
+    This can be used to calcualte graph isomorphism across time without needing to save the entire graph.
+
+    :param graph: graph to hash
+    :type graph: graph
+
+    :return: integer hash
+    :rtype: int
+    """
+    # Copy graph to memory (improved performance if graph is backed by a DB store)
+    graph_prime = copy_graph(graph)
+    triple_canonicalizer = _TripleCanonicalizer(graph_prime)
+
+    return triple_canonicalizer.to_hash()