feat: Context managers (#4073)

closes #4053

```
from ansys.fluent.core import launch_fluent
from ansys.fluent.core import examples
from ansys.fluent.core.solver import *

import_filename = examples.download_file(
    "elbow.cas.h5",
    "pyfluent/examples/DOE-ML-Mixing-Elbow",
)

solver = launch_fluent()

with using(solver):
    ReadCase(import_filename)
    assert Setup() == solver.setup
    assert Viscous().model() == "laminar"
```

---------

Co-authored-by: pyansys-ci-bot <[email protected]>

Author: hpohekar

doc/changelog.d/4073.added.md

@@ -0,0 +1 @@
+Context managers

src/ansys/fluent/core/solver/__init__.py

@@ -26,3 +26,5 @@
     from ansys.fluent.core.generated.solver.settings_builtin import *  # noqa: F401, F403
 except (ImportError, AttributeError, SyntaxError):
     pass
+
+from ansys.fluent.core.utils.context_managers import ReadCase, using  # noqa: F401

src/ansys/fluent/core/solver/settings_builtin_bases.py

@@ -26,6 +26,7 @@
 
 from ansys.fluent.core.solver.flobject import NamedObject, SettingsBase
 from ansys.fluent.core.solver.settings_builtin_data import DATA
+from ansys.fluent.core.utils.context_managers import _get_active_session
 from ansys.fluent.core.utils.fluent_version import FluentVersion
 
 
@@ -70,12 +71,19 @@ def _get_settings_obj(settings_root, builtin_settings_obj):
     return obj
 
 
+def _initialize_settings(instance, defaults: dict, settings_source=None, **kwargs):
+    active_session = _get_active_session()
+    instance.__dict__.update(defaults | kwargs)
+    if settings_source is not None:
+        instance.settings_source = settings_source
+    elif active_session:
+        instance.settings_source = active_session
+
+
 class _SingletonSetting:
     # Covers both groups and named-object containers
     def __init__(self, settings_source: SettingsBase | Solver | None = None, **kwargs):
-        self.__dict__.update(dict(settings_source=None) | kwargs)
-        if settings_source is not None:
-            self.settings_source = settings_source
+        _initialize_settings(self, {"settings_source": None}, settings_source, **kwargs)
 
     def __setattr__(self, name, value):
         if name == "settings_source":
@@ -92,9 +100,9 @@ class _NonCreatableNamedObjectSetting:
     def __init__(
         self, name: str, settings_source: SettingsBase | Solver | None = None, **kwargs
     ):
-        self.__dict__.update(dict(settings_source=None, name=name) | kwargs)
-        if settings_source is not None:
-            self.settings_source = settings_source
+        _initialize_settings(
+            self, {"settings_source": None, "name": name}, settings_source, **kwargs
+        )
 
     def __setattr__(self, name, value):
         if name == "settings_source":
@@ -118,12 +126,16 @@ def __init__(
     ):
         if name and new_instance_name:
             raise ValueError("Cannot specify both name and new_instance_name.")
-        self.__dict__.update(
-            dict(settings_source=None, name=name, new_instance_name=new_instance_name)
-            | kwargs
+        _initialize_settings(
+            self,
+            {
+                "settings_source": None,
+                "name": name,
+                "new_instance_name": new_instance_name,
+            },
+            settings_source,
+            **kwargs,
         )
-        if settings_source is not None:
-            self.settings_source = settings_source
 
     def __setattr__(self, name, value):
         if name == "settings_source":

src/ansys/fluent/core/utils/context_managers.py

@@ -0,0 +1,68 @@
+# Copyright (C) 2021 - 2025 ANSYS, Inc. and/or its affiliates.
+# SPDX-License-Identifier: MIT
+#
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+"""Module for context managers used in PyFluent."""
+
+from contextlib import contextmanager
+from threading import local
+
+_thread_local = local()
+
+
+def _get_stack():
+    if not hasattr(_thread_local, "stack"):
+        _thread_local.stack = []
+    return _thread_local.stack
+
+
+@contextmanager
+def using(session):
+    """Context manager to use a Fluent session."""
+    stack = _get_stack()
+    stack.append(session)
+    try:
+        yield
+    finally:
+        stack.pop()
+
+
+def _get_active_session():
+    stack = _get_stack()
+    if stack:
+        return stack[-1]
+
+
+class ReadCase:
+    """Context manager to read a Fluent case file."""
+
+    def __init__(self, session=None, case_file: str | None = None):
+        self.session = session or _get_active_session()
+        self.case_file = case_file
+
+    def __enter__(self):
+        if not self.case_file:
+            raise ValueError("A case file path must be provided to read.")
+        self.session.settings.file.read_case(file_name=self.case_file)
+        return self.session
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        pass

tests/test_builtin_settings.py

@@ -143,6 +143,7 @@
     pass  # for no-codegen testing workflow
 import ansys.fluent.core as pyfluent
 from ansys.fluent.core.examples import download_file
+from ansys.fluent.core.solver import *  # noqa: F401, F403
 from ansys.fluent.core.utils.fluent_version import FluentVersion
 
 
@@ -778,3 +779,50 @@ def test_builtin_creatable_named_object_setting_assign_session(
         report_file.settings_source = solver
         assert report_file == solver.solution.monitor.report_files["report-file-2"]
         assert report_file.settings_source == solver.settings
+
+
+@pytest.mark.codegen_required
+def test_context_manager_1(mixing_elbow_case_data_session):
+    import threading
+
+    solver = mixing_elbow_case_data_session
+
+    # Test that the context manager works with a solver session
+    with using(solver):  # noqa: F405
+        assert Setup() == solver.setup
+        assert General() == solver.setup.general
+        assert Models() == solver.setup.models
+        assert Multiphase() == solver.setup.models.multiphase
+        assert Energy() == solver.setup.models.energy
+        assert Viscous() == solver.setup.models.viscous
+
+    # Test that the context manager works with multiple threads
+    def run_solver_context():
+        with using(solver):  # noqa: F405
+            setup = Setup()
+            print(
+                f"Setup in thread {threading.current_thread().name}: {setup == solver.setup}"
+            )
+
+    threads = [
+        threading.Thread(target=run_solver_context, name=f"Thread-{i}")
+        for i in range(3)
+    ]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+
+@pytest.mark.codegen_required
+def test_context_manager_2(new_solver_session):
+    solver = new_solver_session
+
+    import_filename = download_file(
+        "elbow.cas.h5",
+        "pyfluent/examples/DOE-ML-Mixing-Elbow",
+    )
+
+    with using(solver):  # noqa: F405
+        ReadCase(import_filename)  # noqa: F405
+        assert Viscous().model() == "laminar"