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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 change_charset(s, original_charset, target_charset):
 """ Convert a string from one charset to another. """

    if not isinstance(s, str):
        raise ValueError('"s" must be a string.')

    intermediate_integer = charset_to_int(s, original_charset)
    output_string = int_to_charset(intermediate_integer, target_charset)
    return output_string