Resolve a relative module name to an absolute one.

def _resolve_name(name, package, level):
    """Resolve a relative module name to an absolute one."""
    bits = package.rsplit('.', level - 1)
    if len(bits) < level:
        raise ValueError('attempted relative import beyond top-level package')
    base = bits[0]
    return '{}.{}'.format(base, name) if name else base