added new CrawlSpider that's gonna replace the old CrawlSpider soon

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40415

scrapy/trunk/scrapy/contrib/spiders2.py

@@ -0,0 +1,83 @@
+"""
+This module contains the basic crawling spider that you can use to inherit your
+spider from.
+"""
+
+from scrapy.http import Request
+from scrapy.spider import BaseSpider
+from scrapy.item import ScrapedItem
+
+class CrawlSpider(BaseSpider):
+    """
+    This is the base class for crawling spiders. It is based on a list of
+    crawling rules (stored in the "rules" attribute) which specify how links
+    are extracted and followed, and how pages are processed (by using a
+    callback function).
+
+    For more info about rules see the Rule class.
+    """
+
+    def parse(self, response):
+        """Method called by the framework core for all the start_urls. Do not
+        override this function, override parse_start_url instead.
+        """
+        if response.url in self.start_urls:
+            return self._parse_wrapper(response, self.parse_start_url, cb_kwargs={}, follow=True) 
+        else:
+            return self.parse_url(response)
+
+    def parse_start_url(self, response):
+        """Callback function for processing start_urls. It must return a list
+        of ScrapedItems and/or Requests.
+        """
+        return []
+
+    def _requests_to_follow(self, response):
+        requests = []
+        seen = set()
+        for rule in self.rules:
+            callback = rule.callback if callable(rule.callback) else getattr(self, rule.callback, None)
+            links = [l for l in rule.link_extractor.extract_urls(response) if l not in seen]
+            seen.union(links)
+            for link in links:
+                r = Request(url=link.url, link_text=link.text)
+                r.append_callback(self._parse_wrapper, callback, cb_kwargs=rule.cb_kwargs, follow=rule.follow)
+                requests.append(r)
+        return requests
+
+    def _parse_wrapper(self, response, callback, cb_kwargs, follow):
+        res = []
+        if follow:
+            res.extend(self._requests_to_follow(response))
+        if callback:
+            res.extend(callback(response, **cb_kwargs) or ())
+        return res
+
+
+class Rule(object):
+    """
+    A rule for crawling, which receives the following constructor arguments:
+
+    link_extractor (required)
+       A LinkExtractor which defines the policy for extracting links
+    callback (optional)
+       A function to use to process the page once it has been downloaded. If
+       callback is omitted the page is not procesed, just crawled. If callback
+       is a string (instead of callable) a method of the spider class with that
+       name is used as the callback function
+    cb_kwargs (optional)
+       A dict specifying keyword arguments to pass to the callback function
+    follow (optional)
+       If True, links will be followed from the pages crawled by this rule.
+       It defaults to True when no callback is specified or False when a
+       callback is specified
+    """
+    
+    def __init__(self, link_extractor, callback=None, cb_kwargs=None, follow=None):
+        self.link_extractor = link_extractor
+        self.callback = callback
+        self.cb_kwargs = cb_kwargs or {}
+        if follow is None:
+            self.follow = False if callback else True
+        else:
+            self.follow = follow