XPath：通过当前节点属性选择当前和下一个节点的文本

如果这是一个重复的问题，我很抱歉，但我在 SO 或其他地方找不到另一个问题来处理我需要的内容。这是我的问题：

我在用着scrapy从中获取一些信息this http://www.utm.utoronto.ca/regcal/WEBLISTCOURSES1.html网页。为了清楚起见，以下是该网页的源代码块，我对此感兴趣：

<p class="titlestyle">ANT101H5 Introduction to Biological Anthropology and Archaeology 
                        <span class='distribution'>(SCI)</span></p> 

<span class='normaltext'> 
Anthropology is the global and holistic study of human biology and behaviour, and includes four subfields: biological anthropology, archaeology, sociocultural anthropology and linguistics. The material covered is  directed  to answering the question: What makes us human? This course is a survey of  biological  anthropology and  archaeology.  [<span class='Helpcourse'
            onMouseover="showtip(this,event,'24 Lectures')"
            onMouseout="hidetip()">24L</span>, <span class='Helpcourse'
            onMouseover="showtip(this,event,'12 Tutorials')"
            onMouseout="hidetip()">12T</span>]<br> 

<span class='title2'>Exclusion: </span><a href='javascript:OpenCourse("WEBCOURSENOTFOUND.html")'>ANT100Y5</a><br>

<span class='title2'>Prerequisite: </span><a href='javascript:OpenCourse("WEBCOURSEANT102H5.pl?fv=1")'>ANT102H5</a><br> 
</span><br/><br/<br/> 

该页面上的几乎所有代码都类似于上面的代码块。

从这一切中，我需要抓住：

1. ANT101H5 生物人类学和考古学导论
2. 排除：ANT100Y5
3. 先决条件：ANT102H5

问题是Exclusion:是在一个里面<span class="title2"> and ANT100Y5是在下面的里面<a>.

我似乎无法从源代码中获取它们。目前，我有尝试（但失败）抓取的代码ANT100Y5看起来像：

hxs = HtmlXPathSelector(response)
    sites = hxs.select("//*[(name() = 'p' and @class = 'titlestyle') or (name() = 'a' and @href and preceding-sibling::'//span/@class=title2')]")

我很感激任何对此的帮助，即使它是“你因为没有看到另一个完美回答这个问题的问题而盲目”（在这种情况下，我自己将投票结束这个问题）。我实在是无计可施了。

提前致谢

编辑：在@Dimitre建议的更改后完成原始代码

我正在使用以下代码：

class regcalSpider(BaseSpider):
    name = "disc"
    allowed_domains = ['www.utm.utoronto.ca']
    start_urls = ['http://www.utm.utoronto.ca/regcal/WEBLISTCOURSES1.html']

    def parse(self, response):
            items = []
            hxs = HtmlXPathSelector(response)
            sites = hxs.select("/*/p/text()[1] | \
                              (//span[@class='title2'])[1]/text() | \
                              (//span[@class='title2'])[1]/following-sibling::a[1]/text() | \
                              (//span[@class='title2'])[2]/text() | \
                              (//span[@class='title2'])[2]/following-sibling::a[1]/text()")

            for site in sites:
                    item = RegcalItem()
                    item['title'] = site.select("a/text()").extract()
                    item['link'] = site.select("a/@href").extract()
                    item['desc'] = site.select("text()").extract()
                    items.append(item)
            return items

            filename = response.url.split("/")[-2]
            open(filename, 'wb').write(response.body)

这给了我这个结果：

[{"title": [], "link": [], "desc": []},
 {"title": [], "link": [], "desc": []},
 {"title": [], "link": [], "desc": []}]

这不是我需要的输出。我究竟做错了什么？请记住，我正在运行此脚本this http://www.utm.utoronto.ca/regcal/WEBLISTCOURSES1.html， 如上所述。

.1. ANT101H5 生物人类学和考古学导论

p[@class='titlestyle']/text()

.2.排除：ANT100Y5

concat(
    span/span[@class='title2'][1],
    span/span[@class='title2'][1]/following-sibling::a[1]
    )

.3.先决条件：ANT102H5

concat(
    span/span[@class='title2'][2],
    span/span[@class='title2'][2]/following-sibling::a[1]
    )