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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 format_back( number: FormatArg, light: Optional[bool] = False, extended: Optional[bool] = False) -> str: """ Return an escape code for a back color, by number. This is a convenience method for handling the different code types all in one shot. It also handles some validation. """

    return _format_code(
        number,
        backcolor=True,
        light=light,
        extended=extended
    )