Revert "gh-130914: Make graphlib.TopologicalSorter.prepare() idempotent (#131317)"

This reverts commit c1b42db.

Author: sebbASF

Doc/library/graphlib.rst

@@ -106,14 +106,6 @@
       function, the graph cannot be modified, and therefore no more nodes can be
       added using :meth:`~TopologicalSorter.add`.
 
-      A :exc:`ValueError` will be raised if the sort has been started by
-      :meth:`~.static_order` or :meth:`~.get_ready`.
-
-      .. versionchanged:: next
-
-         ``prepare()`` can now be called more than once as long as the sort has
-         not started. Previously this raised :exc:`ValueError`.
-
    .. method:: is_active()
 
       Returns ``True`` if more progress can be made and ``False`` otherwise.

Doc/whatsnew/3.14.rst

@@ -607,15 +607,6 @@ getopt
 * Add support for returning intermixed options and non-option arguments in order.
   (Contributed by Serhiy Storchaka in :gh:`126390`.)
 
-
-graphlib
---------
-
-* Allow :meth:`graphlib.TopologicalSorter.prepare` to be called more than once
-  as long as sorting has not started.
-  (Contributed by Daniel Pope in :gh:`130914`)
-
-
 http
 ----
 

Lib/graphlib.py

@@ -90,17 +90,13 @@ def prepare(self):
         still be used to obtain as many nodes as possible until cycles block more
         progress. After a call to this function, the graph cannot be modified and
         therefore no more nodes can be added using "add".
-
-        Raise ValueError if nodes have already been passed out of the sorter.
-
         """
-        if self._npassedout > 0:
-            raise ValueError("cannot prepare() after starting sort")
+        if self._ready_nodes is not None:
+            raise ValueError("cannot prepare() more than once")
 
-        if self._ready_nodes is None:
-            self._ready_nodes = [
-                i.node for i in self._node2info.values() if i.npredecessors == 0
-            ]
+        self._ready_nodes = [
+            i.node for i in self._node2info.values() if i.npredecessors == 0
+        ]
         # ready_nodes is set before we look for cycles on purpose:
         # if the user wants to catch the CycleError, that's fine,
         # they can continue using the instance to grab as many

Lib/test/test_graphlib.py

@@ -140,21 +140,9 @@ def test_calls_before_prepare(self):
     def test_prepare_multiple_times(self):
         ts = graphlib.TopologicalSorter()
         ts.prepare()
-        ts.prepare()
-
-    def test_prepare_after_pass_out(self):
-        ts = graphlib.TopologicalSorter({'a': 'bc'})
-        ts.prepare()
-        self.assertEqual(set(ts.get_ready()), {'b', 'c'})
-        with self.assertRaisesRegex(ValueError, r"cannot prepare\(\) after starting sort"):
+        with self.assertRaisesRegex(ValueError, r"cannot prepare\(\) more than once"):
             ts.prepare()
 
-    def test_prepare_cycleerror_each_time(self):
-        ts = graphlib.TopologicalSorter({'a': 'b', 'b': 'a'})
-        for attempt in range(1, 4):
-            with self.assertRaises(graphlib.CycleError, msg=f"{attempt=}"):
-                ts.prepare()
-
     def test_invalid_nodes_in_done(self):
         ts = graphlib.TopologicalSorter()
         ts.add(1, 2, 3, 4)

Misc/ACKS

@@ -1483,7 +1483,6 @@ Michael Pomraning
 Martin Pool
 Iustin Pop
 Claudiu Popa
-Daniel Pope
 Nick Pope
 John Popplewell
 Matheus Vieira Portela