从我们这个小游戏的词汇扫描器中，我们应该可以得到类似下面的列表:
>>> from ex48 import lexicon
>>> print lexicon.scan("go north")
[('verb', 'go'), ('direction', 'north')]
>>> print lexicon.scan("kill the princess")
[('verb', 'kill'), ('stop', 'the'), ('noun', 'princess')]
>>> print lexicon.scan("open the door and smack the bear in the nose")
[('error', 'open'), ('stop', 'the'), ('error', 'door'), ('error', 'and'), ('error', 'smack'), ('stop', 'the'), ('noun', 'bear'), ('stop', 'in'), ('stop', 'the'), ('error', 'nose')]
在我们的项目目录中添加ex49文件夹，在该目录下创建init.py和parser.py文件,内容如下：
##-- coding: utf-8 --
class ParserError(Exception):
pass
class Sentence(object):
def __init__(self,subject,verb,object):
#remember we take ('noun','princess') tuples and convert them
self.subject = subject[1]
self.verb = verb[1]
self.object = object[1]
#word_list是待解析元祖列表
#返回元祖列表的第一个元祖的第一个元素
def peek(word_list):
if word_list:
word = word_list[0]
return word[0]
else:
return None
#如果元祖列表不为空，将第一个元祖出栈，并与给定的类型进行对比，符合则返回该元祖；否则返回None
def match(word_list,expecting):
if word_list:
word = word_list.pop(0)
if word[0] == expecting:
return word
else:
return None
else:
return None
#遍历元祖列表，如果列表内元祖的类型与给定的类型符合，就将该元祖出栈，并返回该元祖
def skip(word_list,word_type):
while peek(word_list) == word_type:
match(word_list,word_type)
#首先将元祖列表中的类型为‘stop’的元祖出栈，接着如果元祖列表的第一个元祖类型类型为'verb'，则返回该元祖，否则抛出异常
def parse_verb(word_list):
skip(word_list,'stop')
if peek(word_list) == 'verb':
return match(word_list,'verb')
else:
raise ParserError("Expected a verb next.")
#首先将元祖列表中的类型为‘stop’的元祖出栈，接着如果元祖列表的第一个元祖类型类型为'noun'或者'direction‘则返回该元祖
def parse_object(word_list):
skip(word_list,'stop')
next = peek(word_list)
if next == 'noun':
return match(word_list,'noun')
if next == 'direction':
return match(word_list,'direction')
else:
raise ParserError("Expected a noun or direction next.")
#分别将解析出的'verb','noun'/'direction'类型的元祖+给定的主语，组合成句子
def parse_subject(word_list,subj):
verb = parse_verb(word_list)
obj = parse_object(word_list)
return Sentence(subj,verb,obj)
#如果元祖列表第一个元祖的类型是‘noun’，则作为主语调用parse_subject方法组成句子；
#如果第一个词的类型是‘verb’就将('noun','player')作为主语，组成句子。否则抛出异常
def parse_sentence(word_list):
skip(word_list,'stop')
start = peek(word_list)
if start == 'noun':
subj = match(word_list, 'noun')
return parse_subject(word_list,subj)
elif start == 'verb':
#assume the subject is the player then
return parse_subject(word_list,('noun','player'))
else:
raise ParserError("Must start with subject,object,or verb not: %s" % start)
同时在tests文件夹下创建ex49_tests.py文件，内容如下
from nose.tools import *
from ex49 import parser
def test_Sentence():
sen = parser.Sentence(('noun','bear'),('verb','go'),('direction','north'))
assert_equal(sen.subject, 'bear')
assert_equal(sen.verb,'go')
assert_equal(sen.object,'north')
def test_peek():
assert_equal(parser.peek([('noun','bear')]),'noun')
assert_equal(parser.peek([('verb','go'),('direction','north')]),'verb')
assert_equal(parser.peek([('stop','of'),('number','123'),('noun','bear')]),'stop')
assert_equal(parser.peek([]), None)
def test_match():
assert_equal(parser.match([('direction','south')],'direction'),('direction','south'))
assert_equal(parser.match([('stop','in'),('verb','go')],'stop'),('stop','in'))
assert_equal(parser.match([('stop','of'),('direction','north'),('verb','go')],'stop'),('stop','of'))
assert_equal(parser.match([('stop','in'),('verb','go')],'noun'), None)
def test_parse_verb():
assert_equal(parser.parse_verb([('stop', 'of'), ('verb', 'go'), ('direction', 'north')]), ('verb', 'go'))
assert_equal(parser.parse_verb([('stop', 'in'), ('verb', 'come'), ('direction', 'north')]), ('verb', 'come'))
assert_raises(parser.ParserError, parser.parse_verb, [('stop', 'in'), ('number', 123), ('noun', 'princess')])
def test_parse_object():
assert_equal(parser.parse_object([('stop', 'of'), ('direction', 'north'), ('verb', 'go')]),('direction', 'north'))
assert_equal(parser.parse_object([('stop', 'in'),('noun', 'bear'), ('verb', 'come')]),('noun', 'bear'))
assert_raises(parser.ParserError, parser.parse_object,[('verb', 'kill'), ('stop', 'of'), ('verb', 'go')])
def test_parse_subject():
sentence = parser.parse_subject([('stop', 'of'), ('verb', 'go'), ('direction', 'north')],('noun','princess'))
assert_equal(sentence.subject,'princess')
assert_equal(sentence.verb,'go')
assert_equal(sentence.object,'north')
sentence2 = parser.parse_subject([('stop', 'in'), ('verb', 'kill'), ('noun', 'bear')],('noun','princess'))
assert_equal(sentence2.subject, 'princess')
assert_equal(sentence2.verb, 'kill')
assert_equal(sentence2.object, 'bear')
def test_parse_sentence():
sentence1 = parser.parse_sentence([('stop', 'in'), ('noun', 'bear'), ('verb', 'kill'),('direction','south')])
assert_equal(sentence1.subject, 'bear')
assert_equal(sentence1.verb, 'kill')
assert_equal(sentence1.object, 'south')
sentence2 = parser.parse_sentence([('verb', 'kill'), ('stop', 'of'), ('noun', 'bear')])
assert_equal(sentence2.subject, 'player')
assert_equal(sentence2.verb,'kill')
assert_equal(sentence2.object,'bear')
assert_raises(parser.ParserError, parser.parse_sentence,[('stop', 'the'), ('stop', 'of'), ('direction', 'west'), ('verb', 'go')])
执行结果：
/simplegame$ nosetests
................
----------------------------------------------------------------------
Ran 16 tests in 0.010s
OK
加分习题
- 修改parse_函数(方法)，将它们放到一个类里边，而不仅仅是独立的方法函数。 这两种程序设计你喜欢哪一种呢?
- 提高 parser 对于错误输入的抵御能力，这样即使用户输入了你预定义语汇之外的
词语，你的程序也能正常运行下去。 - 改进语法，让它可以处理更多的东西，例如数字。
- 想想在游戏里你的 Sentence 类可以对用户输入做哪些有趣的事情。
