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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _extract_shifted_mean_gauss(image, mask = slice(None), offset = None, sigma = 1, voxelspacing = None):
 """ Internal, single-image version of `shifted_mean_gauss`. """
    
    # set voxel spacing
    if voxelspacing is None:
        voxelspacing = [1.] * image.ndim
    # set offset
    if offset is None:
        offset = [0] * image.ndim
    
    # determine gaussian kernel size in voxel units
    sigma = _create_structure_array(sigma, voxelspacing)
    
    # compute smoothed version of image
    smoothed = gaussian_filter(image, sigma)
    
    shifted = numpy.zeros_like(smoothed)
    in_slicer = []
    out_slicer = []
    for o in offset:
        in_slicer.append(slice(o, None))
        out_slicer.append(slice(None, -1 * o))
    shifted[out_slicer] = smoothed[in_slicer]
    
    return _extract_intensities(shifted, mask)