<filename>ropy/backend/__init__.py
from ropy.backend.PyPlot import *
from ropy.backend.urdf import *

try:
    from ropy.backend.Sim import *
except ImportError:
    pass

<filename>ropy/backend/__init__.py
from ropy.backend.PyPlot import *
from ropy.backend.urdf import *

try:
    from ropy.backend.Sim import *
except ImportError:
    pass
