fix stackoverflow and add comments

searx/engines/stackoverflow.py

+## Stackoverflow (It)
+# 
+# @website     https://stackoverflow.com/
+# @provide-api not clear (https://api.stackexchange.com/docs/advanced-search)
+# 
+# @using-api   no
+# @results     HTML
+# @stable      no (HTML can change)
+# @parse       url, title, content
+
 from urlparse import urljoin
 from cgi import escape
 from urllib import urlencode
 from lxml import html
 
+# engine dependent config
 categories = ['it']
+paging = True
 
+# search-url
 url = 'http://stackoverflow.com/'
 search_url = url+'search?{query}&page={pageno}'
-result_xpath = './/div[@class="excerpt"]//text()'
 
-paging = True
+# specific xpath variables
+results_xpath = '//div[contains(@class,"question-summary")]'
+link_xpath = './/div[@class="result-link"]//a|.//div[@class="summary"]//h3//a'
+title_xpath = './/text()'
+content_xpath = './/div[@class="excerpt"]//text()'
 
 
+# do search-request
 def request(query, params):
     params['url'] = search_url.format(query=urlencode({'q': query}),
                                       pageno=params['pageno'])
+
     return params
 
 
+# get response from search-request
 def response(resp):
     results = []
+
     dom = html.fromstring(resp.text)
-    for result in dom.xpath('//div[@class="question-summary search-result"]'):
-        link = result.xpath('.//div[@class="result-link"]//a')[0]
+
+    # parse results
+    for result in dom.xpath(results_xpath):
+        link = result.xpath(link_xpath)[0]
         href = urljoin(url, link.attrib.get('href'))
-        title = escape(' '.join(link.xpath('.//text()')))
-        content = escape(' '.join(result.xpath(result_xpath)))
-        results.append({'url': href, 'title': title, 'content': content})
+        title = escape(' '.join(link.xpath(title_xpath)))
+        content = escape(' '.join(result.xpath(content_xpath)))
+
+        # append result
+        results.append({'url': href, 
+                        'title': title, 
+                        'content': content})
+
+    # return results
     return results

searx/settings.yml

 
   - name : stackoverflow
     engine : stackoverflow
-    categories : it
     shortcut : st
 
   - name : startpage