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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 process_list_arg(arg):
 """ Parse a string into a list separated by commas with whitespace stripped """

    if isinstance(arg, list):
        return arg
    elif isinstance(arg, basestring):
        args = []
        for part in arg.split(","):
            args.append(part.strip())
        return args