Hierarchy and Traversal

USD Stages are organized in a hierarchy of Prims: there is a special root prim at / and it may have N-number of direct Prim descendants, each of which can have their own tree of Prim descendants.

The path to a Prim is described by a string which starts with the root prim / and contains the Prim name separated by the path separator / until the last component is the desired Prim’s name.

For example /Car/Wheel/Tire refers to the Tire prim which has parent Wheel and grandparent Car. Car’s parent is the special root prim /.

In the Tutorial section on Stages there is information on how to retrieve a Prim at a given path using stage_ref.GetPrimAtPath().

Here is a refresher, we’ll assume car.usda has the /Car/Wheel/Tire path:

from pxr import Usd

stage_ref = Usd.Stage.Open('car.usda')

prim_ref = stage_ref.GetPrimAtPath('/Car')

Now, if you want to get a specific child of a Prim, and you know the name, you can use prim_ref.GetChild(child_name):

from pxr import Usd

stage_ref = Usd.Stage.Open('car.usda')

prim_ref = stage_ref.GetPrimAtPath('/Car')
child_prim_ref = prim_ref.GetChild('Wheel')

# Prims can be cast as bool, so you can check if the prim exists by comparing
its bool() overload
if child_prim_ref:
    print("/Car/Wheel exists") # this will execute

print(child_prim_ref.GetPath()) # prints ""/Car/Wheel"

If you want to get all the children of a Prim, you can use prim_ref.GetChildren() which returns a list of prim references:

from pxr import Usd

stage_ref = Usd.Stage.Open('car.usda')

prim_ref = stage_ref.GetPrimAtPath('/Car')

# will return [Usd.Prim(</Car/Wheel>)]
children_refs = prim_ref.GetChildren()

If you want to traverse the entire stage, the stage_ref.Traverse() function is perfect for that, it returns an iterator:

from pxr import Usd

stage_ref = Usd.Stage.Open('car.usda')

for prim_ref in stage_ref.Traverse():
    print(prim_ref.GetPath())

There are more advanced traversal methods described in the UsdStage documentation.