reverse property

src/daglib/dag.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from collections import defaultdict
 from collections.abc import Iterable, Iterator, MutableMapping, MutableSet
-from typing import Generic, Set, TypeVar
+from typing import Generic, TypeVar
 
 from .set import DAGSet
 
@@ -20,8 +20,12 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
     """
 
     def __init__(self) -> None:
-        self._succ: defaultdict[T, Set[T]] = defaultdict(set)
-        self.reverse: defaultdict[T, Set[T]] = defaultdict(set)
+        self._succ: defaultdict[T, set[T]] = defaultdict(set)
+        self._pred: defaultdict[T, set[T]] = defaultdict(set)
+
+    @property
+    def reverse(self) -> defaultdict[T, set[T]]:
+        return self._pred
 
     # --- MutableMapping interface ---
 
@@ -30,12 +34,12 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
 
         def on_add(v: T) -> None:
             self._succ[u].add(v)
-            self.reverse[v].add(u)
+            self._pred[v].add(u)
             print(f"Adding edge {u} -> {v}")
 
         def on_remove(v: T) -> None:
             self._succ[u].remove(v)
-            self.reverse[v].remove(u)
+            self._pred[v].remove(u)
             print(f"Removing edge {u} -> {v}")
 
         dagset.on_add = on_add
@@ -67,21 +71,21 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
 
         if u not in self._succ:
             self._succ[u] = set()
-        if v not in self.reverse:
-            self.reverse[v] = set()
+        if v not in self._pred:
+            self._pred[v] = set()
 
         if v not in self._succ[u]:
             self._succ[u].add(v)
-            self.reverse[v].add(u)
+            self._pred[v].add(u)
 
         # Touch keys so nodes appear if accessed later (optional but nice)
         _ = self._succ[v]
-        _ = self.reverse[u]
+        _ = 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)
-            self.reverse[v].discard(u)
+            self._pred[v].discard(u)
         elif not missing_ok:
             raise KeyError((u, v))
 
@@ -90,8 +94,8 @@ class DAG(Generic[T], MutableMapping[T, MutableSet[T]]):
         for v in list(self._succ.get(u, ())):
             self.remove_edge(u, v, missing_ok=True)
         # remove incoming
-        for p in list(self.reverse.get(u, ())):
+        for p in list(self._pred.get(u, ())):
             self.remove_edge(p, u, missing_ok=True)
 
         self._succ.pop(u, None)
-        self.reverse.pop(u, None)
+        self._pred.pop(u, None)