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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(path, filename):
 """ Backup a file. """

    target = os.path.join(path, filename)
    if os.path.isfile(target):
        dt = datetime.now()
        new_filename = ".{0}.{1}.{2}".format(
            filename, dt.isoformat(), "backup"
        )
        destination = os.path.join(path, new_filename)
        puts("- Backing up {0} to {1}".format(
            colored.cyan(target),
            colored.cyan(destination)
        ))

        shutil.copy(target, destination)