title: scrapy tutorial error when running crawl
body: <p>I'm trying to run the scrapy tutorial and receive this error everytime I try to run: </p>
  
  <pre><code>PALOMARESR-LALM:scrapy_tutorial brian$ scrapy crawl dmoz
  2013-09-06 17:48:51-0700 [scrapy] INFO: Scrapy 0.18.2 started (bot: scrapy_tutorial)
  2013-09-06 17:48:51-0700 [scrapy] DEBUG: Optional features available: ssl, http11
  2013-09-06 17:48:51-0700 [scrapy] DEBUG: Overridden settings: {'NEWSPIDER_MODULE': 'scrapy_tutorial.spiders', 'SPIDER_MODULES': ['scrapy_tutorial.spiders'], 'BOT_NAME': 'scrapy_tutorial'}
  2013-09-06 17:48:51-0700 [scrapy] DEBUG: Enabled extensions: LogStats, TelnetConsole, CloseSpider, WebService, CoreStats, SpiderState
  Traceback (most recent call last):
    File "/usr/local/bin/scrapy", line 5, in &lt;module&gt;
      pkg_resources.run_script('Scrapy==0.18.2', 'scrapy')
    File "build/bdist.macosx-10.8-intel/egg/pkg_resources.py", line 492, in run_script
  
    File "build/bdist.macosx-10.8-intel/egg/pkg_resources.py", line 1350, in run_script
      for name in eagers:
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/EGG-INFO/scripts/scrapy", line 4, in &lt;module&gt;
      execute()
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/cmdline.py", line 142, in execute
      _run_print_help(parser, _run_command, cmd, args, opts)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/cmdline.py", line 88, in _run_print_help
      func(*a, **kw)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/cmdline.py", line 149, in _run_command
      cmd.run(args, opts)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/commands/crawl.py", line 50, in run
      self.crawler_process.start()
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/crawler.py", line 93, in start
      if self.start_crawling():
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/crawler.py", line 168, in start_crawling
      return self.start_crawler() is not None
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/crawler.py", line 151, in start_crawler
      crawler.configure()
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/crawler.py", line 45, in configure
      self.engine = ExecutionEngine(self, self._spider_closed)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/engine.py", line 62, in __init__
      self.downloader = Downloader(crawler)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/downloader/__init__.py", line 73, in __init__
      self.handlers = DownloadHandlers(crawler)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/downloader/handlers/__init__.py", line 18, in __init__
      cls = load_object(clspath)
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/utils/misc.py", line 38, in load_object
      mod = __import__(module, {}, {}, [''])
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/downloader/handlers/s3.py", line 4, in &lt;module&gt;
      from .http import HTTPDownloadHandler
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/downloader/handlers/http.py", line 5, in &lt;module&gt;
      from .http11 import HTTP11DownloadHandler as HTTPDownloadHandler
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/core/downloader/handlers/http11.py", line 13, in &lt;module&gt;
      from scrapy.xlib.tx import Agent, ProxyAgent, ResponseDone, \
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/xlib/tx/__init__.py", line 6, in &lt;module&gt;
      from . import client, endpoints
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/xlib/tx/client.py", line 37, in &lt;module&gt;
      from .endpoints import TCP4ClientEndpoint, SSL4ClientEndpoint
    File "/Library/Python/2.7/site-packages/Scrapy-0.18.2-py2.7.egg/scrapy/xlib/tx/endpoints.py", line 222, in &lt;module&gt;
      interfaces.IProcessTransport, '_process')):
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/zope/interface/declarations.py", line 495, in __call__
      raise TypeError("Can't use implementer with classes.  Use one of "
  TypeError: Can't use implementer with classes.  Use one of the class-declaration functions instead.
  </code></pre>
  
  <p>I'm running on OS X and the scrapy version info is below:</p>
  
  <pre><code>PALOMARESR-LALM:~ brian$ scrapy version -v
  Scrapy  : 0.18.2
  lxml    : 3.2.3.0
  libxml2 : 2.7.8
  Twisted : 12.0.0
  Python  : 2.7.2 (default, Oct 11 2012, 20:14:37) - [GCC 4.2.1 Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)]
  Platform: Darwin-12.4.0-x86_64-i386-64bit
  </code></pre>
  
  <p>Can someone please assist? Thanks in advance!</p>