def list_projection(values, columns): #--------------------------------------<<<
    """Return a comma-delimited string containing specified values from a list.

    values = list of values. (E.g., as returned from a csv.reader().)
    columns = list of indices (0-based) for the columns that are to be included
              in the returned line.

    Returns a comma-delimited text string containing only the desired columns
    in the order specified in the passed list.
    """
    returned = []
    for column in columns:
        returned.append(values[column])
    return ','.join(returned)