Context managers and default sessions

[seanpearsonuk]

This discussion covers two related topics that intersect in user experience and API ergonomics:

• Managing a default Fluent session in PyFluent

• Using a context manager to temporarily switch sessions

Here's a preview of what this might look like in use:

from ansys.fluent.core.solver import *

# Automatically launches Fluent using default config (if not already running)
ReadCase("elbow.cas.h5")
Viscous().model = "k-epsilon"

from ansys.fluent.core import launch_fluent
solver2 = launch_fluent()  # explicit launch of another session

# Temporarily use the second session
with using(solver2):
    ReadCase("pipe.cas.h5")
    Viscous().model = "SST k-omega"

# Reverts back to the original session
Viscous().model = "k-epsilon"

Requirements

• Provide a using(session) context manager to control the active solver session.
• Support implicit Fluent launch based on default or user-provided configuration (e.g., Fluent version, mode).
• Manage a current default solver session (thread-local) to enable usage of built-in settings classes without explicitly passing settings_source.

Advantages

• Cleaner and more intuitive usage of built-in settings objects (Viscous(), BoundaryConditions(), etc.) without boilerplate.
• Faster and simpler onboarding for new users by removing the need for an explicit launch step in basic workflows.
• Better Jupyter notebook and scripting experience, especially for exploratory use or education.

Drawbacks

• Partial applicability: This mechanism would initially only apply to built-in solver settings classes. Other APIs would require the session object to be specified, potentially causing confusion.
• Global state risks: Managing a global (or thread-local) default session may lead to user error in complex scripts or multi-session workflows if session context isn’t clearly managed or documented.

Notes

While these two ideas — context-managed session switching and implicit default session management — complement each other, they can be considered independently. In particular, context management could be useful even without a default session.