How to use the specutils.spectra.SpectralRegion function in specutils

-----
    The spectrum will need to have the uncertainty defined in order for the SNR
    to be calculated. If the goal is instead signal to noise *per pixel*, this
    should be computed directly as ``spectrum.flux / spectrum.uncertainty``.

    """

    if not hasattr(spectrum, 'uncertainty') or spectrum.uncertainty is None:
        raise Exception("Spectrum1D currently requires the uncertainty be defined.")

    # No region, therefore whole spectrum.
    if region is None:
        return _snr_single_region(spectrum)

    # Single region
    elif isinstance(region, SpectralRegion):
        return _snr_single_region(spectrum, region=region)

    # List of regions
    elif isinstance(region, list):
        return [_snr_single_region(spectrum, region=reg)
                for reg in region]

Centroid of the spectrum or within the regions

    Notes
    -----
    The spectrum will need to be continuum subtracted before calling
    this method. See the
    `analysis documentation `_ for more information.

    """

    # No region, therefore whole spectrum.
    if region is None:
        return _centroid_single_region(spectrum)

    # Single region
    elif isinstance(region, SpectralRegion):
        return _centroid_single_region(spectrum, region=region)

    # List of regions
    elif isinstance(region, list):
        return [_centroid_single_region(spectrum, region=reg)
                for reg in region]

The DER_SNR algorithm is an unbiased estimator describing the spectrum
    as a whole as long as the noise is uncorrelated in wavelength bins spaced
    two pixels apart, the noise is Normal distributed, for large wavelength
    regions, the signal over the scale of 5 or more pixels can be approximated
    by a straight line.

    Code and some docs copied from
    ``http://www.stecf.org/software/ASTROsoft/DER_SNR/der_snr.py``
    """

    # No region, therefore whole spectrum.
    if region is None:
        return _snr_derived(spectrum)

    # Single region
    elif isinstance(region, SpectralRegion):
        return _snr_derived(spectrum, region=region)

    # List of regions
    elif isinstance(region, list):
        return [_snr_derived(spectrum, region=reg)
                for reg in region]

-------
    spectrum : `~specutils.Spectrum1D`
        Output `~specutils.Spectrum1D` with the region excised.

    Raises
    ------
    ValueError
       In the case that ``spectrum`` and ``region`` are not the correct types.

    """

    # Parameter checks
    if not isinstance(spectrum, Spectrum1D):
        raise ValueError('The spectrum parameter must be a Spectrum1D object.')

    if not isinstance(region, SpectralRegion):
        raise ValueError('The region parameter must be a SpectralRegion object.')

    #
    #  Call the exciser method
    #

    return exciser(spectrum, region)