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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 _create_list(value, allow_filename=False):
 """Create a list from the input value. If the input is a list already, return it. If the input is a comma-separated string, split it. """

    if isinstance(value, list):
        return value
    elif isinstance(value, string_type):
        if allow_filename and os.path.isfile(value):
            with codecs.open(value, 'r', encoding="utf-8") as handle:
                return handle.read().splitlines()
        return value.split(',')
    else:
        raise ValueError("Can't create list for input {}".format(value))