bpo-17005: Move topological sort functionality to its own module (GH-20558)

The topological sort functionality that was introduced initially in the
functools module has been moved to a new graphlib module to
better accommodate the new tools and keep the original scope of the
functools module. 

1 files changed, 244 insertions, 0 deletions

diff --git a/Lib/test/test_graphlib.py b/Lib/test/test_graphlib.py
new file mode 100644
index 0000000..0043253
--- /dev/null
+++ b/Lib/test/test_graphlib.py
@@ -0,0 +1,244 @@
+from itertools import chain
+import graphlib
+import os
+import unittest
+
+from test.support.script_helper import assert_python_ok
+
+class TestTopologicalSort(unittest.TestCase):
+    def _test_graph(self, graph, expected):
+        def static_order_with_groups(ts):
+            ts.prepare()
+            while ts.is_active():
+                nodes = ts.get_ready()
+                for node in nodes:
+                    ts.done(node)
+                yield nodes
+
+        ts = graphlib.TopologicalSorter(graph)
+        self.assertEqual(list(static_order_with_groups(ts)), list(expected))
+
+        ts = graphlib.TopologicalSorter(graph)
+        self.assertEqual(list(ts.static_order()), list(chain(*expected)))
+
+    def _assert_cycle(self, graph, cycle):
+        ts = graphlib.TopologicalSorter()
+        for node, dependson in graph.items():
+            ts.add(node, *dependson)
+        try:
+            ts.prepare()
+        except graphlib.CycleError as e:
+            msg, seq = e.args
+            self.assertIn(" ".join(map(str, cycle)), " ".join(map(str, seq * 2)))
+        else:
+            raise
+
+    def test_simple_cases(self):
+        self._test_graph(
+            {2: {11}, 9: {11, 8}, 10: {11, 3}, 11: {7, 5}, 8: {7, 3}},
+            [(3, 5, 7), (11, 8), (2, 10, 9)],
+        )
+
+        self._test_graph({1: {}}, [(1,)])
+
+        self._test_graph(
+            {x: {x + 1} for x in range(10)}, [(x,) for x in range(10, -1, -1)]
+        )
+
+        self._test_graph(
+            {2: {3}, 3: {4}, 4: {5}, 5: {1}, 11: {12}, 12: {13}, 13: {14}, 14: {15}},
+            [(1, 15), (5, 14), (4, 13), (3, 12), (2, 11)],
+        )
+
+        self._test_graph(
+            {
+                0: [1, 2],
+                1: [3],
+                2: [5, 6],
+                3: [4],
+                4: [9],
+                5: [3],
+                6: [7],
+                7: [8],
+                8: [4],
+                9: [],
+            },
+            [(9,), (4,), (3, 8), (1, 5, 7), (6,), (2,), (0,)],
+        )
+
+        self._test_graph({0: [1, 2], 1: [], 2: [3], 3: []}, [(1, 3), (2,), (0,)])
+
+        self._test_graph(
+            {0: [1, 2], 1: [], 2: [3], 3: [], 4: [5], 5: [6], 6: []},
+            [(1, 3, 6), (2, 5), (0, 4)],
+        )
+
+    def test_no_dependencies(self):
+        self._test_graph({1: {2}, 3: {4}, 5: {6}}, [(2, 4, 6), (1, 3, 5)])
+
+        self._test_graph({1: set(), 3: set(), 5: set()}, [(1, 3, 5)])
+
+    def test_the_node_multiple_times(self):
+        # Test same node multiple times in dependencies
+        self._test_graph({1: {2}, 3: {4}, 0: [2, 4, 4, 4, 4, 4]}, [(2, 4), (1, 3, 0)])
+
+        # Test adding the same dependency multiple times
+        ts = graphlib.TopologicalSorter()
+        ts.add(1, 2)
+        ts.add(1, 2)
+        ts.add(1, 2)
+        self.assertEqual([*ts.static_order()], [2, 1])
+
+    def test_graph_with_iterables(self):
+        dependson = (2 * x + 1 for x in range(5))
+        ts = graphlib.TopologicalSorter({0: dependson})
+        self.assertEqual(list(ts.static_order()), [1, 3, 5, 7, 9, 0])
+
+    def test_add_dependencies_for_same_node_incrementally(self):
+        # Test same node multiple times
+        ts = graphlib.TopologicalSorter()
+        ts.add(1, 2)
+        ts.add(1, 3)
+        ts.add(1, 4)
+        ts.add(1, 5)
+
+        ts2 = graphlib.TopologicalSorter({1: {2, 3, 4, 5}})
+        self.assertEqual([*ts.static_order()], [*ts2.static_order()])
+
+    def test_empty(self):
+        self._test_graph({}, [])
+
+    def test_cycle(self):
+        # Self cycle
+        self._assert_cycle({1: {1}}, [1, 1])
+        # Simple cycle
+        self._assert_cycle({1: {2}, 2: {1}}, [1, 2, 1])
+        # Indirect cycle
+        self._assert_cycle({1: {2}, 2: {3}, 3: {1}}, [1, 3, 2, 1])
+        # not all elements involved in a cycle
+        self._assert_cycle({1: {2}, 2: {3}, 3: {1}, 5: {4}, 4: {6}}, [1, 3, 2, 1])
+        # Multiple cycles
+        self._assert_cycle({1: {2}, 2: {1}, 3: {4}, 4: {5}, 6: {7}, 7: {6}}, [1, 2, 1])
+        # Cycle in the middle of the graph
+        self._assert_cycle({1: {2}, 2: {3}, 3: {2, 4}, 4: {5}}, [3, 2])
+
+    def test_calls_before_prepare(self):
+        ts = graphlib.TopologicalSorter()
+
+        with self.assertRaisesRegex(ValueError, r"prepare\(\) must be called first"):
+            ts.get_ready()
+        with self.assertRaisesRegex(ValueError, r"prepare\(\) must be called first"):
+            ts.done(3)
+        with self.assertRaisesRegex(ValueError, r"prepare\(\) must be called first"):
+            ts.is_active()
+
+    def test_prepare_multiple_times(self):
+        ts = graphlib.TopologicalSorter()
+        ts.prepare()
+        with self.assertRaisesRegex(ValueError, r"cannot prepare\(\) more than once"):
+            ts.prepare()
+
+    def test_invalid_nodes_in_done(self):
+        ts = graphlib.TopologicalSorter()
+        ts.add(1, 2, 3, 4)
+        ts.add(2, 3, 4)
+        ts.prepare()
+        ts.get_ready()
+
+        with self.assertRaisesRegex(ValueError, "node 2 was not passed out"):
+            ts.done(2)
+        with self.assertRaisesRegex(ValueError, r"node 24 was not added using add\(\)"):
+            ts.done(24)
+
+    def test_done(self):
+        ts = graphlib.TopologicalSorter()
+        ts.add(1, 2, 3, 4)
+        ts.add(2, 3)
+        ts.prepare()
+
+        self.assertEqual(ts.get_ready(), (3, 4))
+        # If we don't mark anything as done, get_ready() returns nothing
+        self.assertEqual(ts.get_ready(), ())
+        ts.done(3)
+        # Now 2 becomes available as 3 is done
+        self.assertEqual(ts.get_ready(), (2,))
+        self.assertEqual(ts.get_ready(), ())
+        ts.done(4)
+        ts.done(2)
+        # Only 1 is missing
+        self.assertEqual(ts.get_ready(), (1,))
+        self.assertEqual(ts.get_ready(), ())
+        ts.done(1)
+        self.assertEqual(ts.get_ready(), ())
+        self.assertFalse(ts.is_active())
+
+    def test_is_active(self):
+        ts = graphlib.TopologicalSorter()
+        ts.add(1, 2)
+        ts.prepare()
+
+        self.assertTrue(ts.is_active())
+        self.assertEqual(ts.get_ready(), (2,))
+        self.assertTrue(ts.is_active())
+        ts.done(2)
+        self.assertTrue(ts.is_active())
+        self.assertEqual(ts.get_ready(), (1,))
+        self.assertTrue(ts.is_active())
+        ts.done(1)
+        self.assertFalse(ts.is_active())
+
+    def test_not_hashable_nodes(self):
+        ts = graphlib.TopologicalSorter()
+        self.assertRaises(TypeError, ts.add, dict(), 1)
+        self.assertRaises(TypeError, ts.add, 1, dict())
+        self.assertRaises(TypeError, ts.add, dict(), dict())
+
+    def test_order_of_insertion_does_not_matter_between_groups(self):
+        def get_groups(ts):
+            ts.prepare()
+            while ts.is_active():
+                nodes = ts.get_ready()
+                ts.done(*nodes)
+                yield set(nodes)
+
+        ts = graphlib.TopologicalSorter()
+        ts.add(3, 2, 1)
+        ts.add(1, 0)
+        ts.add(4, 5)
+        ts.add(6, 7)
+        ts.add(4, 7)
+
+        ts2 = graphlib.TopologicalSorter()
+        ts2.add(1, 0)
+        ts2.add(3, 2, 1)
+        ts2.add(4, 7)
+        ts2.add(6, 7)
+        ts2.add(4, 5)
+
+        self.assertEqual(list(get_groups(ts)), list(get_groups(ts2)))
+
+    def test_static_order_does_not_change_with_the_hash_seed(self):
+        def check_order_with_hash_seed(seed):
+            code = """if 1:
+                import graphlib
+                ts = graphlib.TopologicalSorter()
+                ts.add('blech', 'bluch', 'hola')
+                ts.add('abcd', 'blech', 'bluch', 'a', 'b')
+                ts.add('a', 'a string', 'something', 'b')
+                ts.add('bluch', 'hola', 'abcde', 'a', 'b')
+                print(list(ts.static_order()))
+                """
+            env = os.environ.copy()
+            # signal to assert_python not to do a copy
+            # of os.environ on its own
+            env["__cleanenv"] = True
+            env["PYTHONHASHSEED"] = str(seed)
+            out = assert_python_ok("-c", code, **env)
+            return out
+
+        run1 = check_order_with_hash_seed(1234)
+        run2 = check_order_with_hash_seed(31415)
+
+        self.assertNotEqual(run1, "")
+        self.assertNotEqual(run2, "")
+        self.assertEqual(run1, run2)