types

src/daglib/dag.py

@@ -6,6 +6,8 @@ from typing import Generic, TypeVar
 
 from .set import DAGSet
 
+type dictset = defaultdict[T, set[T]]
+
 T = TypeVar("T")
 
 
@@ -19,12 +21,15 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
     a guarded view that keeps reverse in sync.
     """
 
+    _succ: dictset[T]
+    _pred: dictset[T]
+
     def __init__(self) -> None:
-        self._succ: defaultdict[T, set[T]] = defaultdict(set)
-        self._pred: defaultdict[T, set[T]] = defaultdict(set)
+        self._succ: dictset[T] = defaultdict(set)
+        self._pred: dictset[T] = defaultdict(set)
 
     @property
-    def reverse(self) -> defaultdict[T, set[T]]:
+    def reverse(self) -> dictset[T]:
         return self._pred
 
     # --- MutableMapping interface ---
@@ -78,10 +83,6 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
             self._succ[u].add(v)
             self._pred[v].add(u)
 
-        # Touch keys so nodes appear if accessed later (optional but nice)
-        _ = self._succ[v]
-        _ = self._pred[u]
-
     def remove_edge(self, u: T, v: T, *, missing_ok: bool = True) -> None:
         if v in self._succ.get(u, ()):
             self._succ[u].remove(v)