def convert_semester(str):
    """
    Convert the abbreviated semester form "2015fa" from an Informer report
    into a more readable, human-friendly form "2015 Fall"
    """
    year = str[:4]
    season = str.lower()[-2:]
    if season == 'fa':
        return 'Fall ' + year
    elif season == 'sp':
        return 'Spring ' + year
    elif season == 'su':
        return 'Summer ' + year
    # something's gone wrong if we get this far, so throw an error
    else:
        raise Exception('invalid semester season string %s' % season)