added ItemSamplerPipeline

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40344

scrapy/trunk/scrapy/contrib/itemsampler.py

@@ -0,0 +1,87 @@
+"""
+This module provides a mechanism for collecting one (or more) sample items per
+domain.
+
+The items are collected in a dict of guid->item and persisted by pickling that
+dict into a file.
+
+This can be useful for testing changes made to the framework or other common
+code that affects several spiders.
+
+It uses the scrapy stats service to keep track of which domains are already
+sampled.
+
+Settings that affect this module:
+
+ITEMSAMPLER_FILE
+  file where to store the pickled dict of scraped items
+"""
+
+from __future__ import with_statement
+
+import cPickle as pickle
+
+from pydispatch import dispatcher
+
+from scrapy.core.engine import scrapyengine
+from scrapy.core.exceptions import NotConfigured, DropItem
+from scrapy.core import signals
+from scrapy.stats import stats
+from scrapy import log
+from scrapy.conf import settings
+
+items_per_domain = settings.getint('ITEMSAMPLER_COUNT', 1)
+close_domain = settings.getbool('ITEMSAMPLER_CLOSE_DOMAIN', False)
+
+class ItemSamplerPipeline(object):
+
+    def __init__(self):
+        self.filename = settings['ITEMSAMPLER_FILE']
+        if not self.filename:
+            raise NotConfigured
+        self.items = {}
+        self.domains_count = 0
+        self.empty_domains = set()
+        dispatcher.connect(self.domain_closed, signal=signals.domain_closed)
+        dispatcher.connect(self.engine_stopped, signal=signals.engine_stopped)
+
+    def process_item(self, domain, response, item):
+        sampled = stats.getpath("%s/items_sampled" % domain, 0)
+        if sampled < items_per_domain:
+            self.items[item.guid] = item
+            sampled += 1
+            stats.setpath("%s/items_sampled" % domain, sampled)
+            if close_domain and sampled == items_per_domain:
+                scrapyengine.close_domain(domain)
+        return item
+
+    def engine_stopped(self):
+        with open(self.filename, 'w') as f:
+            pickle.dump(self.items, f)
+        if self.empty_domains:
+            log.msg("Empty domains (no items scraped) found: %s" % " ".join(self.empty_domains), level=log.WARNING)
+
+    def domain_closed(self, domain, spider, status):
+        if status == 'finished' and not stats.getpath("%s/items_sampled" % domain):
+            self.empty_domains.add(domain)
+        self.domains_count += 1
+        log.msg("Sampled %d domains so far (%d empty)" % (self.domains_count, len(self.empty_domains)), level=log.INFO)
+
+
+class ItemSamplerMiddleware(object):
+    """This middleware drops items and requests (when domain sampling has been
+    completed) to accelerate the processing of remaining domains"""
+
+    def __init__(self):
+        if not settings['ITEMSAMPLER_FILE']:
+            raise NotConfigured
+
+    def process_scrape(self, response, spider):
+        if stats.getpath("%s/items_sampled" % spider.domain_name) >= items_per_domain:
+            return []
+
+    def process_result(self, response, result, spider):
+        if stats.getpath("%s/items_sampled" % spider.domain_name) >= items_per_domain:
+            return []
+        else:
+            return result