title: Scrapy: all scrapers failed. Spider with syntax error
body: <p>Sometimes I get fail of all scrapers when in one scraper exist some error.
  Example:
  I have scrapers with syntax error which was missed.</p>
  
  <pre><code>class MySpiderWithSyntaxError(scrapy.Spider):
      name = "my_spider_with_syntax_error"
  
      start_urls = [
          'http://www.website.com'
      ]
  
      def parse(self response):
          for url in response.css('a.p::attr(href)').extract():
              print url
  </code></pre>
  
  <p>In this spider missed comma in line </p>
  
  <pre><code>def parse(self response):
  </code></pre>
  
  <p>And spider MySpiderWithSyntaxError will fail.
  But if run another spider without syntax error (spider code below)</p>
  
  <pre><code>class MySpiderWithoutSyntaxError(scrapy.Spider):
      name = "my_spider_without_syntax_error"
  
      start_urls = [
          'http://www.website.com'
      ]
  
      def parse(self, response):
          for url in response.css('a.p::attr(href)').extract():
              print url
  </code></pre>
  
  <p>I get error like that:</p>
  
  <pre><code>    Traceback (most recent call last):
      File "/home/Documents/project/.env/bin/scrapy", line 11, in &lt;module&gt;
         sys.exit(execute())
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/cmdline.py", line 141, in execute
         cmd.crawler_process = CrawlerProcess(settings)
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/crawler.py", line 238, in __init__
         super(CrawlerProcess, self).__init__(settings)
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/crawler.py", line 129, in __init__
         self.spider_loader = _get_spider_loader(settings)
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/crawler.py", line 325, in _get_spider_loader
         return loader_cls.from_settings(settings.frozencopy())
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/spiderloader.py", line 33, in from_settings
         return cls(settings)
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/spiderloader.py", line 20, in __init__
         self._load_all_spiders()
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/spiderloader.py", line 28, in _load_all_spiders
         for module in walk_modules(name):
      File "/home/Documents/project/.env/local/lib/python2.7/site-packages/scrapy/utils/misc.py", line 71, in walk_modules
         submod = import_module(fullpath)
      File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
         __import__(name)
      File "/home/Documents/project/scrapers/scrapy/spiders/my_spider_with_syntax_error.py", line 14
         def parse(self response):
                       ^
      SyntaxError: invalid syntax
  </code></pre>
  
  <p>Question:
  Is it possible to catch errors like that and fail only spider with syntax error but another spiders work fine?</p>