Splits a string in the format "a,b,c,d,e,f" into
    ['a', 'b', 'c', 'd', 'e', 'f', ]

def list_from_env(key, default=""):
    """
    Splits a string in the format "a,b,c,d,e,f" into
    ['a', 'b', 'c', 'd', 'e', 'f', ]
    """
    try:
        val = os.environ.get(key, default)
        return val.split(',')
    except (KeyError, ValueError):
        return []