title: Scrapy: TypeError: __init__() missing 1 required positional argument: 'settings'
body: <p>I have a Scrapy middleware:</p>
  
  <pre><code>class ProxyMiddleware(object):
      def __init__(self, settings):
          self.proxy_file = settings.get('PROXY_FILE')
          fin = open(self.proxy_file)
          self.proxy_list = list()
          for line in fin.readlines():
              parts = line.strip().split()
              proxy = parts[2] + '://' + parts[0] + ':' + parts[1]
              self.proxy_list.append(proxy)
  
      def process_request(self, request, spider):
          request.meta['proxy'] = random.choice(self.proxy_list)
  </code></pre>
  
  <p>But an error occurred when running, what's the settings?</p>