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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_median(image, mask = slice(None), size = 1, voxelspacing = None):
 """ Internal, single-image version of `median`. """

    # set voxel spacing
    if voxelspacing is None:
        voxelspacing = [1.] * image.ndim
        
    # determine structure element size in voxel units
    size = _create_structure_array(size, voxelspacing)
        
    return _extract_intensities(median_filter(image, size), mask)