求解：Scrapy爬虫运行报错ImportError: No module named _util

按照指南上搭建好了Scrapy的环境，该装的都装好了，参考教程是：

http://scrapy-chs.readthedocs.io/zh_CN/0.24/intro/tutorial.html

按照第一个Spider代码练习，保存在 tutorial/spiders 目录下的 dmoz_spider.py 文件中:

import scrapy

class DmozSpider(scrapy.Spider):
    name = "dmoz"
    allowed_domains = ["dmoz.org"]
    start_urls = [
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
        "http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
    ]

    def parse(self, response):
        filename = response.url.split("/")[-2]
        with open(filename, 'wb') as f:
            f.write(response.body) 

再进入项目的根目录，执行命令scrapy crawl dmoz，目的时为了crawl dmoz启动爬虫

正常情况下得到的输出应该是：

2014-01-23 18:13:07-0400 [scrapy] INFO: Scrapy started (bot: tutorial)
2014-01-23 18:13:07-0400 [scrapy] INFO: Optional features available: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Overridden settings: {}
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled extensions: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled downloader middlewares: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled spider middlewares: ...
2014-01-23 18:13:07-0400 [scrapy] INFO: Enabled item pipelines: ...
2014-01-23 18:13:07-0400 [dmoz] INFO: Spider opened
2014-01-23 18:13:08-0400 [dmoz] DEBUG: Crawled (200) <GET http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/> (referer: None)
2014-01-23 18:13:09-0400 [dmoz] DEBUG: Crawled (200) <GET http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> (referer: None)
2014-01-23 18:13:09-0400 [dmoz] INFO: Closing spider (finished)

然而实际不是，实际报错：

alicedeMacBook-Pro:tutorial alice$ scrapy crawl dmoz
2018-08-06 22:25:23 [scrapy.utils.log] INFO: Scrapy 1.5.1 started (bot: tutorial)
2018-08-06 22:25:23 [scrapy.utils.log] INFO: Versions: lxml 4.2.4.0, libxml2 2.9.8, cssselect 1.0.3, parsel 1.5.0, w3lib 1.19.0, Twisted 18.7.0, Python 2.7.10 (default, Jul 15 2017, 17:16:57) - [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)], pyOpenSSL 0.13.1 (LibreSSL 2.2.7), cryptography unknown, Platform Darwin-17.3.0-x86_64-i386-64bit
2018-08-06 22:25:23 [scrapy.crawler] INFO: Overridden settings: {'NEWSPIDER_MODULE': 'tutorial.spiders', 'SPIDER_MODULES': ['tutorial.spiders'], 'ROBOTSTXT_OBEY': True, 'BOT_NAME': 'tutorial'}
Traceback (most recent call last):
  File "/usr/local/bin/scrapy", line 11, in <module>
    sys.exit(execute())
  File "/Library/Python/2.7/site-packages/scrapy/cmdline.py", line 150, in execute
    _run_print_help(parser, _run_command, cmd, args, opts)
  File "/Library/Python/2.7/site-packages/scrapy/cmdline.py", line 90, in _run_print_help
    func(*a, **kw)
  File "/Library/Python/2.7/site-packages/scrapy/cmdline.py", line 157, in _run_command
    cmd.run(args, opts)
  File "/Library/Python/2.7/site-packages/scrapy/commands/crawl.py", line 57, in run
    self.crawler_process.crawl(spname, **opts.spargs)
  File "/Library/Python/2.7/site-packages/scrapy/crawler.py", line 170, in crawl
    crawler = self.create_crawler(crawler_or_spidercls)
  File "/Library/Python/2.7/site-packages/scrapy/crawler.py", line 198, in create_crawler
    return self._create_crawler(crawler_or_spidercls)
  File "/Library/Python/2.7/site-packages/scrapy/crawler.py", line 203, in _create_crawler
    return Crawler(spidercls, self.settings)
  File "/Library/Python/2.7/site-packages/scrapy/crawler.py", line 55, in __init__
    self.extensions = ExtensionManager.from_crawler(self)
  File "/Library/Python/2.7/site-packages/scrapy/middleware.py", line 58, in from_crawler
    return cls.from_settings(crawler.settings, crawler)
  File "/Library/Python/2.7/site-packages/scrapy/middleware.py", line 34, in from_settings
    mwcls = load_object(clspath)
  File "/Library/Python/2.7/site-packages/scrapy/utils/misc.py", line 44, in load_object
    mod = import_module(module)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/Library/Python/2.7/site-packages/scrapy/extensions/memusage.py", line 16, in <module>
    from scrapy.mail import MailSender
  File "/Library/Python/2.7/site-packages/scrapy/mail.py", line 25, in <module>
    from twisted.internet import defer, reactor, ssl
  File "/Library/Python/2.7/site-packages/twisted/internet/ssl.py", line 230, in <module>
    from twisted.internet._sslverify import (
  File "/Library/Python/2.7/site-packages/twisted/internet/_sslverify.py", line 15, in <module>
    from OpenSSL._util import lib as pyOpenSSLlib
ImportError: No module named _util

网上查了很久的资料，仍然无解。部分博主说是pyOpenSSL或Scrapy的安装有问题，于是重新装了pyOpenSSL和Scrapy，但还是报同样错误，实在不知道怎么解决了。