References within maya can be referred to by Path or by Reference Node. The latter one is a stable entity in your scene, whereas the first one is dependent on the amount of references as well as the actual reference file.
Dealing with references correctly can be complex in times, but the FileReference type in MRV greatly facilitates this.
Maya organizes its references hierarchically, which can be queried using the iDagItem interface of the FileReference type. Additional functionality includes reference creation, import, removal as well as to query information and to iterate its contained nodes.
The example uses files from the test system and respective utilities:
from mrv.maya.ref import FileReference
refa = FileReference.create(get_maya_file('ref8m.ma')) # file with 8 meshes
refb = FileReference.create(get_maya_file('ref2re.ma')) # two subreferences with subreferences
assert refb.isLoaded()
assert len(FileReference.ls()) == 2
assert len(refa.children()) == 0 and len(refb.children()) == 2
subrefa, subrefb = refb.children()
assert subrefa.namespace() != subrefb.namespace()
assert subrefa.path() == subrefb.path()
assert subrefa.parent() == refb
refa.setLoaded(False)
assert not refa.isLoaded()
assert refa.setLoaded(True).isLoaded()
assert len(list(refa.iterNodes(api.MFn.kMesh))) == 8
refa.remove(); refb.remove()
assert not refa.exists() and not refb.exists()
assert len(FileReference.ls()) == 0