Get properties from codeless schema applied to prim

Community USD
1

With a codeless schema USD plugin, I can check if a prim is using a typed schema by checking the type name and check for an API/applied schema by getting the list of applied schemas.

Is there a better way to check for the typed and API schemas are applied, and how do I get the properties of those schema?

e.g. API schema has three properties, float A, str B, int C. How would I get a list of these properties if I only have a prim in the stage with that API schema applied?

2

One way is to usd the SchemaRegistry

from pxr import Usd
registry = Usd.SchemaRegistry()
skel_bind_def = registry.FindAppliedAPIPrimDefinition("SkelBindingAPI")
print(skel_bind_def.GetPropertyNames())
joints = skel_bind_def.GetSchemaPropertySpec("primvars:skel:jointIndices")
print(joints.valueType)

the skel_bind_def will be a pxr.Usd.PrimDefinition

another good resource:

Maybe someone knows a nicer way? I’ve not encountered a nice pythonic class for codeless schemas…hopefuly there is one, but I suspect that is the trade off of codeless / code based schemas…

3

Those are great sugs, @patricknagle ! There is a more direct way, though, through each prim’s PrimTypeInfo and PrimDefinition, and also the Usd.Prim.Is() and Usd.Prim.HasAPI() methods:

from pxr import Usd
if prim.HasAPI("MyCodelessSchema"):
    # PrimTypeInfo has methods for enumerating the typed and *all* applied schemas...
    primTypeInfo = prim.GetPrimTypeInfo()
    
    # and also access to the PrimDefinition, which will enumerate all the schema 
    # properties (and more).  You can also retrieve the primDefinition directly from
    # Usd.Prim.GetPrimDefinition()
    primDefinition = primTypeInfo.GetPrimDefinition()

Cheers,
–spiff

4

I should have noted, though, that the technique I showed above will return all the properties of all the applied schemas. If you need to isolate just the ones of a particular API schema, then you can still use HasAPI() to quickly find the prims of interest, but you’ll still need to refer to the SchemaRegistry as @patricknagle showed, to enumerate just those properties. I think it might be a nice addition to add a UsdPrimDefinition::GetAppliedSchemaDefinitions() ?

5

That would be nice to have!

I wish there was an easy way to something like

prim = stage.GetPrimAtPath("/world/characters/bob")
codeless_schema = prim.GetAppliedAPISchema("coolCustomSchema")
# codelss_schema would return a python object with Get/Set functions for each attribute based on the api name?
codeless_schema.GetHeightAttr()
codeless_schema.SetHeightAttr(10)

I assume this is not possible at the moment based on the way codeless schemas are registered or there is just simply no mechanism to dynamically generate python objects from these codeless schemas?

6

That should be possible to do, in either a pure python implementation, or as a python object we construct and return from C++. But we’re curious what the scenario is in which you have a codeless schema that you want to write code against.. we’d imagined that a key reason you’d reach for codeless schemas was that they can be more fluid, without code/API dependencies. If we, even dynamically, construct an API object for a codeless schema, you can start writing code that will break if the schema changes. Thanks!

–spiff

7

Hey,

That is true and would also be true for code based schemas wouldn’t it? Without some kind of schema versioning any removal of an attribute would break any code using those automatically generated Get/Set functions woudn’t it?

Out of curiosity how are unrequired atttributes removed from schmeas in the core of USD? Surely a similar issue exists, but with the ability to preserve the Get/Set methods so any callers of deprecated fields get a warning? Just curious how that has worked over the evolution of USD?