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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 default(thumbnailer, prepared_options, source_filename, thumbnail_extension, **kwargs):
 """ Easy-thumbnails' default name processor. For example: ``source.jpg.100x100_q80_crop_upscale.jpg`` """

    filename_parts = [source_filename]
    if ('%(opts)s' in thumbnailer.thumbnail_basedir or
            '%(opts)s' in thumbnailer.thumbnail_subdir):
        if thumbnail_extension != os.path.splitext(source_filename)[1][1:]:
            filename_parts.append(thumbnail_extension)
    else:
        filename_parts += ['_'.join(prepared_options), thumbnail_extension]
    return '.'.join(filename_parts)