Mac下安装scrapy爬虫框架(Command "python setup.py egg_info" failed with error code 1)

工作空余时间想写个爬虫练手，没想到在安装scrapy的过程中遇到了很多问题，在此记录一下。
1.安装python环境
Mac上自带python2.7，于是这一步省了。

2.安装pip

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
python get-pip.py

3.安装scrapy

pip install scrapy

报错：

Collecting scrapy
  Could not fetch URL https://pypi.python.org/simple/scrapy/: There was a problem confirming the ssl certificate: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:661) - skipping
  Could not find a version that satisfies the requirement scrapy (from versions: )
No matching distribution found for scrapy

看起来像是公司开发网导致的无法下载，我打开了Proxifier，让它走代理服务器，解决。
再次pip install scrapy，又报错：

Collecting scrapy
  Using cached https://files.pythonhosted.org/packages/db/9c/cb15b2dc6003a805afd21b9b396e0e965800765b51da72fe17cf340b9be2/Scrapy-1.5.0-py2.py3-none-any.whl
Collecting pyOpenSSL (from scrapy)
  Using cached https://files.pythonhosted.org/packages/79/db/7c0cfe4aa8341a5fab4638952520d8db6ab85ff84505e12c00ea311c3516/pyOpenSSL-17.5.0-py2.py3-none-any.whl
Collecting queuelib (from scrapy)
  Using cached https://files.pythonhosted.org/packages/4c/85/ae64e9145f39dd6d14f8af3fa809a270ef3729f3b90b3c0cf5aa242ab0d4/queuelib-1.5.0-py2.py3-none-any.whl
Collecting cssselect>=0.9 (from scrapy)
  Using cached https://files.pythonhosted.org/packages/7b/44/25b7283e50585f0b4156960691d951b05d061abf4a714078393e51929b30/cssselect-1.0.3-py2.py3-none-any.whl
Collecting PyDispatcher>=2.0.5 (from scrapy)
  Using cached https://files.pythonhosted.org/packages/cd/37/39aca520918ce1935bea9c356bcbb7ed7e52ad4e31bff9b943dfc8e7115b/PyDispatcher-2.0.5.tar.gz
Collecting Twisted>=13.1.0 (from scrapy)
  Using cached https://files.pythonhosted.org/packages/a2/37/298f9547606c45d75aa9792369302cc63aa4bbcf7b5f607560180dd099d2/Twisted-17.9.0.tar.bz2
    Complete output from command python setup.py egg_info:
    Download error on https://pypi.python.org/simple/incremental/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:661) -- Some packages may not be found!
    Couldn't find index page for 'incremental' (maybe misspelled?)
    Download error on https://pypi.python.org/simple/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:661) -- Some packages may not be found!
    No local packages or working download links found for incremental>=16.10.1
    Traceback (most recent call last):
      File "", line 1, in
      File "/private/var/folders/c_/gmvr6xh546bcm2xtfmpc0q640000gn/T/pip-install-inDShH/Twisted/setup.py", line 21, in
        setuptools.setup(**_setup["getSetupArgs"]())
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 111, in setup
        _setup_distribution = dist = klass(attrs)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/setuptools/dist.py", line 315, in __init__
        self.fetch_build_eggs(attrs['setup_requires'])
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/setuptools/dist.py", line 361, in fetch_build_eggs
        replace_conflicting=True,
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pkg_resources/__init__.py", line 850, in resolve
        dist = best[req.key] = env.best_match(req, ws, installer)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pkg_resources/__init__.py", line 1122, in best_match
        return self.obtain(req, installer)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pkg_resources/__init__.py", line 1134, in obtain
        return installer(requirement)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/setuptools/dist.py", line 429, in fetch_build_egg
        return cmd.easy_install(req)
      File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/setuptools/command/easy_install.py", line 659, in easy_install
        raise DistutilsError(msg)
    distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('incremental>=16.10.1')

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/c_/gmvr6xh546bcm2xtfmpc0q640000gn/T/pip-install-inDShH/Twisted/

从log信息中我们可以看到问题出在Collecting Twisted这一步，看Download error on https://pypi.python.org/simple/: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version 还以为是openssl的问题，然而重新安装了openssl还是报一样的错。
那么我单独安装Twisted试一下？报了一样的错
经过一番焦头烂额的搜索尝试安装了一堆我也不知道干嘛的包，还是没有解决。。

【解决方法】：

第二天早上脑子清楚了，查到了stack overflow上的回答：https://stackoverflow.com/questions/42129767/pip-install-twisted-error-1

I had the same issue on a Mac OSX 10.11.6 in a new virtualenv with a fresh install of Python3.6.1. In my case, I had old versions of the Twisted dependency incremental installed, which prevented the installation.

pip install --upgrade incremental
pip install Twisted

Note I: I was installing a whole array of packages from a requirements file where the same incremental version was specified. I really wonder why the upgrade of incremental helped and have no clue what actually went wrong. If someone can clarify, that would be great.
Note II: Installing incremental ahead of of Twisted seems to be necessary on fresh installs, too [Experienced when working with CentOS7].

意思是说：出现这种问题是因为Twisted所依赖的incremental库本地已经有了一个旧版本（答主也是OSX，旧的incremental很可能是系统自带的），这个旧版本的incremental导致了Twisted安装失败。

那么按照答主所说运行这两条命令：先将incremental升级，再安装Twisted。Twisted安装成功~
然后再一次pip install scrapy，成功！