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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 backup_file(filename):
 """ create a backup of the file desired """

    if not os.path.exists(filename):
        return

    BACKUP_SUFFIX = ".sprinter.bak"

    backup_filename = filename + BACKUP_SUFFIX
    shutil.copyfile(filename, backup_filename)