def import_onnx_modules():
    """ To make sure ONNX is runtime dependency, it is imported used only when needed"""
    try:
        from onnx import helper, numpy_helper, mapping
    except ImportError:
        raise ImportError('Onnx and protobuf need to be installed. ' +
            'Instructions to install - https://github.com/onnx/onnx')
    return helper, numpy_helper, mapping
