安装scrapy，以及出现的错误解决。

首先我是在python3的环境上面完成的。我保留了python2的版本，然后安装Python3的版本。然后在安装scrapy的过程中出现的错误，以及切换python版本后出现的错误。
一、安装python3

cd /usr/local/src/
wget https://www.python.org/ftp/python/3.4.2/Python-3.4.2.tgz
tar -xf Python-3.4.2.tgz
cd Python-3.4.2
./configure --prefix=/usr/local/python3
make && make install
##将python做一个备份，然后把python3的建立一个软连接
mv /usr/bin/python /usr/bin/pythonbak
ln -fs /usr/local/python3/bin/python3 /usr/bin/python
再在终端进入python交互模式，出现的是python3了。
[root@lsf ~]# python
Python 3.4.2 (default, Mar 13 2018, 11:37:48) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more infORMation.

##python升级到3后，yum无法正常使用，此时需要改一个文件
[root@lsf ~]# cat /usr/bin/yum
#!/usr/bin/python2.7
将第一行改为python2.7

二、安装scrapy

##建立pip3的软连接
ln -fs /usr/local/python3/bin/pip3 /usr/bin/pip3
##yum安装依赖包,可以解决编译过程中出现的许多错误
yum install -y gcc openssl-devel libxml2-devel libxslt-devel bzip2-devel bzip2* libffi-devel python-devel openssl-devel pycrypto
##用pip3安装
pip3 install twisted --upgrade
pip3 install cryptography pycrypto
##安装scrapy
pip3 install scrapy
##建立scrapy软连接
ln -fs /usr/local/python3/bin/scrapy /usr/bin/scrapy

三、测试scrapy命令

[root@lsf ~]# scrapy
Scrapy 1.5.0 - no active project

Usage:
  scrapy <command> [options] [args]

Available commands:
  bench         Run quick benchmark test
  fetch         Fetch a URL using the Scrapy downloader
  genspider     Generate new spider using pre-defined templates
  runspider     Run a self-contained spider (without creating a project)
  settings      Get settings values
  shell         Interactive scraping console
  startproject  Create new project
  version       Print Scrapy version
  view          Open URL in browser, as seen by Scrapy

  [ more ]      More commands available when run from project directory

Use "scrapy <command> -h" to see more info about a command
##创建一个scrapy项目
scrapy startproject myfirstpjt
##可能会报错ImportError: cannot import name 'certificate_transparency'
pip3 install pip3 --upgrade
##再次安装scrapy
pip3 install scrapy
##创建项目成功后，会出现下面的文件
[root@lsf test_scrapy]# cd myfirstpjt/
[root@lsf myfirstpjt]# ls
myfirstpjt  scrapy.cfg
[root@lsf myfirstpjt]# cd myfirstpjt/
[root@lsf myfirstpjt]# ls
__init__.py  items.py  middlewares.py  pipelines.py  __pycache__  settings.py  spiders

然后就可以直接使用scrapy命令进行项目管理了。