Framework for Creating Complex Commands

[gswifort]

Framework for Creating Complex Commands

I'm planning to create a simple framework for building complex commands in PyRx. The goal is to make command creation more declarative and user-friendly. Here's what I envision:

Proposed API

class RectCommand(CommandBase):
    base_point = GetPoint(name="base_point", prompt="Specify base point", required=True, allow_kwords=False)
    width = GetDist(name="width", prompt="Specify width", base_pt="base_point", required=True, allow_kwords=True)
    height = GetDist(name="height", prompt="Specify height", base_pt="base_point", required=True, allow_kwords=True)
    rotation = GetAngle(name="rotation", prompt="Specify rotation angle", base_pt="base_point", allow_kwords=True, default=0.0)

@command
def rect():
    cmd = RectCommand()
    cmd.call()
    base_pt = cmd.base_point.value
    width = cmd.width.value
    height = cmd.height.value
    rotation = cmd.rotation.value
    rect = Db.Polyline([...])
    Db.curDb().addToModelspace(rect)

Command Line Interaction

Command: RECT
Specify base point: abc
Please input a point!
Specify base point: 
Specify width or [Width/Height/Rotation]: r
Specify rotation angle or [Width/Height/Rotation] <0.0>: 
Specify width or [Width/Height/Rotation]: 50
Specify height or [Width/Height/Rotation]: 20

Step Definition Classes

Classes like GetPoint, GetDist, GetAngle define command steps with the following parameters:

• name: Used to create keyword (could also be a separate kword argument)
• prompt: Base prompt displayed in command line. The framework automatically adds:
  • Newline at the beginning
  • Keywords in square brackets
  • Default value in angle brackets
  • Colon at the end
• required: Whether the value must be provided by the user
• allow_kwords: Whether switching to another step via keyword is allowed at this stage (keywords are automatically generated from defined steps)
• default: Default value assigned to the step if not required, and displayed to user when they invoke this step via keyword
• verifiable (not shown): Step is not required (may have default value or not), but this step is shown to the user. User can press Enter which results in setting a MISSING value for this step

Context Manager Support

I also plan to add a context manager that allows fine-tuning of pre-defined commands for different scenarios:

@command
def rect2():
    with RectCommand() as cmd:
        cmd.rotation.default = math.radians(45)
    # cmd.call() is automatically called when context manager exits

Benefits

This framework would provide:

1. Declarative command definition - Clear separation between command logic and user interaction
2. Automatic keyword generation - No need to manually handle keyword parsing
3. Consistent user experience - Standardized prompts and interaction patterns
4. Reusable command components - Commands can be easily modified and extended

Questions for Discussion

1. What other step types would be useful? Certainly all defined in pyrx.ed.prompt
2. Should there be support for conditional steps (steps that only appear based on previous choices)?
3. Would you find this approach helpful for your command development?
4. Any suggestions for API improvements or additional features?

[CEXT-Dan]

What other step types would be useful?

You could explore what .NET’s API has to offer with regards prompting, I.e. the PromptOptions class hierarchy in Autodesk.AutoCAD.EditorInput. Additionally, sample ArxSdk\ARX2026\samples\database\ARXDBG\Prompt has a similar prompting class hierarchy in C++.

Should there be support for conditional steps (steps that only appear based on previous choices)?

Yes, it should be part of a prompting framework. It’s hard to do though, one company I worked for had this and it was complex/unintuitive. I would be interesting to see how this can be done in python

Would you find this approach helpful for your command development

Sometimes, though, there are other times where I felt it gets in the way, for example .NET’s implementation of the Editor space seems overly engineered.