treeview - deterministic and new getter (apache#37162)

* treeview - determinist and new getter

* review 1

---------

Co-authored-by: raphaelauv <raphaelauv@users.noreply.github.com>

airflow/models/dag.py

@@ -41,6 +41,7 @@
     Callable,
     Collection,
     Container,
+    Generator,
     Iterable,
     Iterator,
     List,
@@ -2627,15 +2628,25 @@ def pickle(self, session=NEW_SESSION) -> DagPickle:
 
     def tree_view(self) -> None:
         """Print an ASCII tree representation of the DAG."""
+        for tmp in self._generate_tree_view():
+            print(tmp)
 
-        def get_downstream(task, level=0):
-            print((" " * level * 4) + str(task))
+    def _generate_tree_view(self) -> Generator[str, None, None]:
+        def get_downstream(task, level=0) -> Generator[str, None, None]:
+            yield (" " * level * 4) + str(task)
             level += 1
-            for t in task.downstream_list:
-                get_downstream(t, level)
-
-        for t in self.roots:
-            get_downstream(t)
+            for tmp_task in sorted(task.downstream_list, key=lambda x: x.task_id):
+                yield from get_downstream(tmp_task, level)
+
+        for t in sorted(self.roots, key=lambda x: x.task_id):
+            yield from get_downstream(t)
+
+    def get_tree_view(self) -> str:
+        """Return an ASCII tree representation of the DAG."""
+        rst = ""
+        for tmp in self._generate_tree_view():
+            rst += tmp + "\n"
+        return rst
 
     @property
     def task(self) -> TaskDecoratorCollection:

tests/models/test_dag.py

@@ -1422,19 +1422,30 @@ def test_leaves(self):
     def test_tree_view(self):
         """Verify correctness of dag.tree_view()."""
         with DAG("test_dag", start_date=DEFAULT_DATE) as dag:
-            op1 = EmptyOperator(task_id="t1")
+            op1_a = EmptyOperator(task_id="t1_a")
+            op1_b = EmptyOperator(task_id="t1_b")
             op2 = EmptyOperator(task_id="t2")
             op3 = EmptyOperator(task_id="t3")
-            op1 >> op2 >> op3
+            op1_b >> op2
+            op1_a >> op2 >> op3
 
             with redirect_stdout(StringIO()) as stdout:
                 dag.tree_view()
                 stdout = stdout.getvalue()
 
             stdout_lines = stdout.splitlines()
-            assert "t1" in stdout_lines[0]
+            assert "t1_a" in stdout_lines[0]
             assert "t2" in stdout_lines[1]
             assert "t3" in stdout_lines[2]
+            assert "t1_b" in stdout_lines[3]
+            assert dag.get_tree_view() == (
+                "<Task(EmptyOperator): t1_a>\n"
+                "    <Task(EmptyOperator): t2>\n"
+                "        <Task(EmptyOperator): t3>\n"
+                "<Task(EmptyOperator): t1_b>\n"
+                "    <Task(EmptyOperator): t2>\n"
+                "        <Task(EmptyOperator): t3>\n"
+            )
 
     def test_duplicate_task_ids_not_allowed_with_dag_context_manager(self):
         """Verify tasks with Duplicate task_id raises error"""