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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 add(ctx, alias, mapping, backend):
 """ Add a new alias to your configuration file. """

    if not backend:
        backends_list = ctx.obj['settings'].get_backends()
        if len(backends_list) > 1:
            raise click.UsageError(
                "You're using more than 1 backend. Please set the backend to "
                "add the alias to with the --backend option (choices are %s)" %
                ", ".join(dict(backends_list).keys())
            )

    add_mapping(ctx, alias, mapping, backend)