More typing for rdflib.graph

This PR adds a bunch of typing for rdflib.graph, mainly as a baseline
for adding typing to rdflib.store which I will do next.

I have resorted to using type aliases for typing all the functions, in
part because it makes it easier to change in the future, however autodoc
type hints do not work particularly well with this which is why I will
switch to https://github.com/tox-dev/sphinx-autodoc-typehints in a
separate patch.

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

Broken off from RDFLib#1850

rdflib/compare.py

@@ -110,6 +110,8 @@
 if TYPE_CHECKING:
     from _hashlib import HASH
 
+from rdflib._typing import _TripleType
+
 
 def _total_seconds(td):
     result = td.days * 24 * 60 * 60
@@ -281,7 +283,6 @@ def copy(self):
         )
 
 
-_TripleT = List[Node]
 _HashT = Callable[[], "HASH"]
 
 
@@ -326,7 +327,9 @@ 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 +524,7 @@ 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 +534,7 @@ 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 +544,7 @@ 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 +580,9 @@ 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 +593,10 @@ def to_canonical_graph(g1, stats=None):
     return ReadOnlyGraphAggregate([graph])
 
 
-def graph_diff(g1, g2):
+# _GraphT = TypeVar("_GraphT", bound=Graph)
+
+
+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 +610,7 @@ 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 +623,12 @@ 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)