More type hints for rdflib.graph and related

This patch primarily adds more type hints for `rdflib.graph`, but also
adds type hints to some related modules in order to work with the new
type hints for `rdflib.graph`.

I'm mainly doing this as a baseline for adding type hints to
`rdflib.store`.

I have created type aliases to make it easier to type everything
cosnsitently and to make type hints easier easier to change in the
future. The type aliases are private however (i.e. `_`-prefixed) and
should be kept as such for now.

This patch only contains typing changes and does not change runtime
behaviour.

Broken off from RDFLib#1850

rdflib/compare.py

@@ -104,7 +104,7 @@
     Union,
 )
 
-from rdflib.graph import ConjunctiveGraph, Graph, ReadOnlyGraphAggregate
+from rdflib.graph import ConjunctiveGraph, Graph, ReadOnlyGraphAggregate, _TripleType
 from rdflib.term import BNode, IdentifiedNode, Node, URIRef
 
 if TYPE_CHECKING:
@@ -281,7 +281,6 @@ def copy(self):
         )
 
 
-_TripleT = List[Node]
 _HashT = Callable[[], "HASH"]
 
 
@@ -326,7 +325,9 @@ def _initial_color(self) -> List[Color]:
                     self._neighbors[p].add(p)
         if len(bnodes) > 0:
             return [Color(list(bnodes), self.hashfunc, hash_cache=self._hash_cache)] + [
-                Color([x], self.hashfunc, x, hash_cache=self._hash_cache)
+                # type error: List item 0 has incompatible type "Union[IdentifiedNode, Literal]"; expected "IdentifiedNode"
+                # type error: Argument 3 to "Color" has incompatible type "Union[IdentifiedNode, Literal]"; expected "Tuple[Tuple[Union[int, str], URIRef, Union[int, str]], ...]"
+                Color([x], self.hashfunc, x, hash_cache=self._hash_cache)  # type: ignore[list-item, arg-type]
                 for x in others
             ]
         else:
@@ -521,7 +522,7 @@ def canonical_triples(self, stats: Optional[Stats] = None):
 
     def _canonicalize_bnodes(
         self,
-        triple: Tuple[IdentifiedNode, IdentifiedNode, Node],
+        triple: "_TripleType",
         labels: Dict[Node, str],
     ):
         for term in triple:
@@ -531,7 +532,7 @@ def _canonicalize_bnodes(
                 yield term
 
 
-def to_isomorphic(graph):
+def to_isomorphic(graph: Graph) -> IsomorphicGraph:
     if isinstance(graph, IsomorphicGraph):
         return graph
     result = IsomorphicGraph()
@@ -541,7 +542,7 @@ def to_isomorphic(graph):
     return result
 
 
-def isomorphic(graph1, graph2):
+def isomorphic(graph1: Graph, graph2: Graph) -> bool:
     """Compare graph for equality.
 
     Uses an algorithm to compute unique hashes which takes bnodes into account.
@@ -577,7 +578,9 @@ def isomorphic(graph1, graph2):
     return gd1 == gd2
 
 
-def to_canonical_graph(g1, stats=None):
+def to_canonical_graph(
+    g1: Graph, stats: Optional[Stats] = None
+) -> ReadOnlyGraphAggregate:
     """Creates a canonical, read-only graph.
 
     Creates a canonical, read-only graph where all bnode id:s are based on
@@ -588,7 +591,7 @@ def to_canonical_graph(g1, stats=None):
     return ReadOnlyGraphAggregate([graph])
 
 
-def graph_diff(g1, g2):
+def graph_diff(g1: Graph, g2: Graph) -> Tuple[Graph, Graph, Graph]:
     """Returns three sets of triples: "in both", "in first" and "in second"."""
     # bnodes have deterministic values in canonical graphs:
     cg1 = to_canonical_graph(g1)
@@ -602,7 +605,7 @@ def graph_diff(g1, g2):
 _MOCK_BNODE = BNode()
 
 
-def similar(g1, g2):
+def similar(g1: Graph, g2: Graph):
     """Checks if the two graphs are "similar".
 
     Checks if the two graphs are "similar", by comparing sorted triples where
@@ -615,12 +618,12 @@ def similar(g1, g2):
     return all(t1 == t2 for (t1, t2) in _squashed_graphs_triples(g1, g2))
 
 
-def _squashed_graphs_triples(g1, g2):
+def _squashed_graphs_triples(g1: Graph, g2: Graph):
     for (t1, t2) in zip(sorted(_squash_graph(g1)), sorted(_squash_graph(g2))):
         yield t1, t2
 
 
-def _squash_graph(graph):
+def _squash_graph(graph: Graph):
     return (_squash_bnodes(triple) for triple in graph)