import sys

if '_stackless' in sys.builtin_module_names:

    # when running on top of a pypy with stackless support

    from _stackless import greenlet

elif hasattr(sys, 'pypy_objspaceclass'):

    raise ImportError("Detected pypy without stackless support")

else:

    # regular CPython

    import py

    gdir = py.path.local(py.__file__).dirpath() 

    path = gdir.join('c-extension', 'greenlet', 'greenlet.c')

    greenlet = path._getpymodule().greenlet