lex を試す。複数のクラスを記述

一つのファイルに複数のクラスを記述

#!/usr/bin/env python

import ply.lex as lex

class MyLexer1:
    tokens = (
      'A',
      'PLUS',
    )
    
    t_A    = r'a'
    t_PLUS = r'\+'
    
    def t_error(self,t):
        print "Illegal character '%s'" % t.value[0]
        t.lexer.skip(1)
    
    # Build the lexer
    def build(self,**kwargs):
        self.lexer = lex.lex(object=self, **kwargs)
    
    # Test it output
    def test(self,data):
        self.lexer.input(data)
        while 1:
             tok = self.lexer.token()
             if not tok: break
             print tok

class MyLexer2:
    tokens = (
      'B',
      'PLUS',
    )
    
    t_B    = r'b'
    t_PLUS = r'\+'
    
    def t_error(self,t):
        print "Illegal character '%s'" % t.value[0]
        t.lexer.skip(1)
    
    # Build the lexer
    def build(self,**kwargs):
        self.lexer = lex.lex(object=self, **kwargs)
    
    # Test it output
    def test(self,data):
        self.lexer.input(data)
        while 1:
             tok = self.lexer.token()
             if not tok: break
             print tok

# Build the lexer and try it out
m1 = MyLexer1()
m1.build()
m1.test("a+a")

m2 = MyLexer2()
m2.build()
m2.test("a+a")

で、

./20080324_ply00.py:37: Rule t_PLUS redefined. Previously defined on line 12
./20080324_ply00.py:39: Rule t_error redefined. Previously defined on line 14

とエラーが出てダメだった。
クラス内だけを見るようになっていないの？(←ソース見ろ)