Get the Child of a Prim

An example of hierarchy and traversal within a smaller scope is getting the child of a prim. These snippets show how to get a single child by name or how to iterate through all of the children of a prim.

USD Python

If you know the name of the child prim, you can use Usd.Prim.GetChild(). This returns an invalid prim if the child doesn’t exist. You can check if the returned prim exists.

from pxr import Usd

def get_child_prim(parent_prim, child_name) -> Usd.Prim:
    child_prim: Usd.Prim = parent_prim.GetChild(child_name)  
    return child_prim

#############
# Full Usage
#############

from pxr import Sdf, UsdGeom

# Create an in-memory Stage with /World Xform prim as the default prim
stage: Usd.Stage = Usd.Stage.CreateInMemory()
default_prim: Usd.Prim = UsdGeom.Xform.Define(stage, Sdf.Path("/World")).GetPrim()
stage.SetDefaultPrim(default_prim)

# Create a Cube prim
cube: Usd.Prim = UsdGeom.Cube.Define(stage, default_prim.GetPath().AppendPath("Box"))

# Get the child prim of the default prim with the name "Box"
child_prim = get_child_prim(default_prim, "Box")

# Print the full Stage
usda = stage.GetRootLayer().ExportToString()
print(usda)
# Print the path of the child prim you were looking for.
print(child_prim.GetPath())

# Verify the child and parent relationship
assert child_prim.GetParent() == default_prim
assert child_prim.GetPath() == cube.GetPath()

Another option is to iterate through all of the prim’s children to operate on all the children or query them to find the child you are looking for.

from pxr import Usd, UsdGeom

def get_first_child_mesh(parent_prim: Usd.Prim) -> Usd.Prim:
    # Iterates only active, loaded, defined, non-abstract children
    for child_prim in parent_prim.GetChildren():
        if child_prim.IsA(UsdGeom.Mesh):
            return child_prim

def print_all_children_names(parent_prim: Usd.Prim):
    # Iterates over all children
    for child_prim in parent_prim.GetAllChildren():
        print(child_prim.GetName())

USDA

This is an example USDA result to show that the Cube prim is the Child Prim of World.

#usda 1.0
(
    defaultPrim = "World"
)

def Xform "World"
{
    def Xform "Cube"
    {
    }
}