fromitem_list : fromitem_list ',' fromitem
                     | fromitem

def p_fromitem_list(self,t):
    """fromitem_list : fromitem_list ',' fromitem
                     | fromitem
    """
    if len(t)==2: t[0] = [t[1]]
    elif len(t)==4: t[0] = t[1] + [t[3]]
    else: raise NotImplementedError('unk_len', len(t)) # pragma: no cover