registers our fancy importer that can let us import from a module name,
    like:

        import sh
        tmp = sh()
        from tmp import ls

def register_importer():
    """ registers our fancy importer that can let us import from a module name,
    like:

        import sh
        tmp = sh()
        from tmp import ls
    """

    def test(importer):
        return importer.__class__.__name__ == ModuleImporterFromVariables.__name__
    already_registered = any([True for i in sys.meta_path if test(i)])

    if not already_registered:
        importer = ModuleImporterFromVariables(
            restrict_to=["SelfWrapper"],
        )
        sys.meta_path.insert(0, importer)

    return not already_registered