features : features AND feature
                    | feature
                    | empty

def p_features(self, t):
        """features : features AND feature
                    | feature
                    | empty"""

        if len(t) == 4:
            t[0] = t[1]
            t[0].append(t[3])
        elif t[1]:
            t[0] = [t[1]]
        else:
            t[0] = []