fix: Update get_si_unit_for_fluent_quantity and from_container (#4573)

---

## Context

Before this change, certain utility functions in PyFluent — specifically
`get_si_unit_for_fluent_quantity` (in `flunits.py`) and `from_container`
(in `session_utilities.py`) — had issues handling units or
container-based settings correctly. For example,
`get_si_unit_for_fluent_quantity` needed better handling when the input
`quantity` was `None`, a list, or an empty string. Also,
`from_container` had parameters or logic that required adjustment for
container-mode launches and file-transfer workflows. The existing
behavior could lead to unexpected results when working with quantity
units or launching sessions with containers.

---

## Change Summary

The PR makes the following changes:

* In `flunits.py`, the `get_si_unit_for_fluent_quantity` function has
been updated to improve handling of various cases: when `quantity` is
`None`, when it's a list (especially an empty list), when it is not a
string, or when it is a string but empty.
* In `session_utilities.py`, the `from_container` function signature
and/or its default parameters were adjusted (added parameters like `gpu:
bool | None = None`, `file_transfer_service: Any | None = None`,
`use_podman_compose: bool | None = None`). This expands the function’s
ability to launch Fluent in container mode with more flexibility.
* A changelog entry (`doc/changelog.d/4573.fixed.md`) was added
summarizing “Update get_si_unit_for_fluent_quantity and from_container”.
* Some tests were modified (in `tests/test_flobject.py`) to reflect
updated behavior or remove outdated assertions.

---

## Rationale

* The `get_si_unit_for_fluent_quantity` change ensures that unit
handling is robust and predictable even for edge cases: lists, `None`,
empty strings. Since PyFluent integrates with the `ansys-units` library
and supports quantity objects, it is important that units are determined
correctly.
* The `from_container` changes are motivated by the need to better
support containerised workflows of Fluent (e.g., using Docker or Podman)
and enabling file transfer services for these sessions. Having
additional parameters gives users more control (GPU usage, whether to
use Docker Compose or Podman Compose, file transfer service) in
launching Fluent via Python.
* Overall, the changes aim to reduce brittleness in unit-handling and
broaden the support of containerised execution scenarios, improving
reliability and usability of PyFluent in advanced workflows.

---

## Impact

* The functions `get_si_unit_for_fluent_quantity` and `from_container`
are internal utilities used by the PyFluent core library
(`ansys.fluent.core`). Workflows that involve retrieving or interpreting
units of Fluent quantities will benefit (or may require slight
adjustments if they relied on previous behavior).
* Session launch workflows, especially those using container mode
(Docker or Podman) or using custom file-transfer services, will see
enhanced capabilities and possibly changed interfaces (because
`from_container` now has more parameters/defaults).
* Test and code-quality improvements: since the tests were adjusted,
developers extending or modifying PyFluent should see fewer false
positives/failures around unit and container-session utilities.
* Downstream code that introspects or depends on unit strings (via
`units()` or `as_quantity()` on settings objects) may need to consider
the changed handling of lists/None/empty strings in
`get_si_unit_for_fluent_quantity`.
* Because these are utility changes rather than front-end user APIs, the
impact on everyday usage of PyFluent (e.g., reading cases, solving) may
be small for many users. But for advanced users leveraging units or
container workflows, the improvements should lead to more predictable
behavior.

---

---------

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

Author: hpohekar

doc/changelog.d/4573.fixed.md

@@ -0,0 +1 @@
+Update get_si_unit_for_fluent_quantity and from_container

src/ansys/fluent/core/session_utilities.py

@@ -190,6 +190,8 @@ def from_container(
         gpu: bool | None = None,
         start_watchdog: bool | None = None,
         file_transfer_service: Any | None = None,
+        use_docker_compose: bool | None = None,
+        use_podman_compose: bool | None = None,
     ):
         """
         Launch a Fluent session in container mode.
@@ -242,6 +244,10 @@ def from_container(
             GUI-less Fluent sessions started by PyFluent are properly closed when the current Python process ends.
         file_transfer_service : Any, optional
             Service for uploading/downloading files to/from the server.
+        use_docker_compose: bool
+            Whether to use Docker Compose to launch Fluent.
+        use_podman_compose: bool
+            Whether to use Podman Compose to launch Fluent.
 
         Returns
         -------

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

@@ -296,9 +296,9 @@ def get_si_unit_for_fluent_quantity(
     """
     # The settings API should return None for the units-quantity
     # attribute only for dimensionless variables
-    if quantity is None:
+    if not quantity:
         return ""
-    if isinstance(quantity, list):  # real vector
+    if isinstance(quantity, list):
         quantity = quantity[0]
     if not isinstance(quantity, str):
         raise InvalidQuantityType(quantity)

tests/test_flobject.py

@@ -1033,7 +1033,6 @@ def _check_vector_units(obj, units):
     assert obj.as_quantity() == ansys.units.Quantity(obj.get_state(), units)
 
 
-@pytest.mark.skip("https://github.com/ansys/pyfluent/issues/4498")
 @pytest.mark.fluent_version(">=24.1")
 def test_ansys_units_integration(mixing_elbow_settings_session):
     solver = mixing_elbow_settings_session