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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 require_backup_exists(func):
 """ Requires that the file referred to by `backup_file` exists in the file system before running the decorated function. """

    def new_func(*args, **kwargs):
        backup_file = kwargs['backup_file']
        if not os.path.exists(backup_file):
            raise RestoreError("Could not find file '{0}'".format(backup_file))
        return func(*args, **kwargs)
    return new_func