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背景：Python很火，且连一些如ESP8266的硬件都支持Python了。
目前Python存在两个版本Python2和Python3系列，且这两个版本同时在更新与维护。到底是选择Python2还是选择Python3，取决于当前要使用的库、框架支持哪个版本。因此一台电脑上可能需要同时安装Python2和Python3两个版本。本文主要讲述的是如何在centos7系统中存在python2系列的同时安装python3.8.1(目前python3系列的最新版本)

1.安装升级相应的软件包
yum install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gcc make

2.下载python 3.8.1 的源码包
wget http://mirrors.sohu.com/python/3.8.1/Python-3.8.1.tgz

3.安装python3.8.1
tar zxvf Python-3.8.1.tgz -C /opt/
cd /opt/Python-3.8.1/  
./configure --prefix=/usr/local/python3
make && make install  

若遇到编译问题：
zipimport.ZipImportError: can't decompress data; zlib not available  #make && make install
yum install zlib zlib-devel -y

4.配置python，配置python3  pip3 软链接，设置软连接：目的是让我们直接在任何地方输入python3命令都可以得到python解释器的运行。
更改/usr/bin/python链接：
ln -s /usr/local/python3/bin/python3.8.1 /usr/bin/python3
ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3
mv /usr/bin/pip{,.backup}
ln -s /usr/local/python3/bin/pip3 /usr/bin/pip   #python2-pip没有，就没有这个pip.
查看是否安装成功
python3 -V
pip3 -V

更改/usr/bin/python默认链接，实现升级：
/usr/bin/python --version
Python 2.7.5
mv /usr/bin/python{,.old.backup}
ln -sf /usr/local/python3/bin/python3.8  /usr/bin/python


5.查看当python的版本,出现版本信息即为正确安装
python3 --version

安装python3.7出现ModuleNotFoundError: No module named '_ctypes'报错(重新编译一次就OK了)
主要是少安装了包： 解决方法： yum install libffi-dev -y yum update -y 然后重新make install即可,如果还报错，在继续安装下其他基础包： yum install make curl curl-devel gcc gcc-c++ gcc-g77 gcc* make zlib-devel bzip2-devel openssl-devel xz-libs wget unzip xz vixie-cron crontabs ntpdate tar lrzsz sysstat bind-utils vim -y yum groupinstall 'development tools' -y yum update -y Centos7.5测试通过· cat ~/.pip/pip.conf [global] timeout = 60 index-url = https://pypi.doubanio.com/simple trusted-host = pypi.doubanio.com 测试：pip install simplejson
来自:https://mhl.xyz/Python/python37_ctypes.html


6.更改yum脚本的python依赖
yum localinstall mysql-5.7.12-171123111505.el7.centos.x86_64.rpm
  File "/usr/libexec/urlgrabber-ext-down", line 28
    except OSError, e:
                  ^
# ls /usr/bin/yum*
# ls yum*
yum yum-config-manager yum-debug-restore yum-groups-manager
yum-builddep yum-debug-dump yumdownloader
更改以上文件头为
#!/usr/bin/python 改为 #!/usr/bin/python2

用Sed 一行搞定，参考自[实践OK]经常用到之linux sed 批量替换字符串,及模糊替换和模糊拼接的例子。http://jackxiang.com/post/2324/：
/usr/bin/yum-groups-manager  #!/usr/bin/python -tt
/usr/bin/yumdownloader #直接python后面有一个空格
/usr/bin/yum-debug-restore #!/usr/bin/python -tt
/usr/bin/yum-debug-dump  #!/usr/bin/python -tt
/usr/bin/yum-config-manager #!/usr/bin/python -tt
/usr/bin/yum-builddep  #!/usr/bin/python -tt
/usr/bin/yum  #python后面无空格
势必要有两种替换：
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-builddep
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-config-manager
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-debug-dump
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-debug-restore
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yumdownloader
sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-groups-manager
sed -i 's/#!\/usr\/bin\/python$/#!\/usr\/bin\/python2.7/' /usr/bin/yum
sed -i 's/#!\/usr\/bin\/python$/#!\/usr\/bin\/python2.7/' /usr/libexec/urlgrabber-ext-down

这个-tt的没有啥用，只是起到警告作用，完全在替换时不要：
-t     Issue a warning when a source file mixes tabs and spaces for indentation in a  way  that  makes  it
              depend on the worth of a tab expressed in spaces.  Issue an error when the option is given twice.
-t 当源文件以制作缩进的方式混合制表符和空格时发出警告
               取决于用空格表示的选项卡的价值。 当该选项被赋予两次时发出一个错误。

7.测试用Python的Pip3安装Python扩展：
rpm -qf /bin/pip
python2-pip-8.1.2-5.el7.noarch
/bin/pip --version
pip 9.0.1 from /usr/lib/python2.7/site-packages (python 2.7)

pip3 --version
pip 9.0.1 from /usr/local/python3/lib/python3.8.1/site-packages (python 3.8.1)

pip3 install PyEmail
Collecting PyEmail
  Downloading https://files.pythonhosted.org/packages/ca/39/caf0436670b6fa9f072e322fab1a2b04d5631bdbdc8ea9857230aae02dd5/PyEmail-0.0.1.zip
Installing collected packages: PyEmail
  Running setup.py install for PyEmail ... done
Successfully installed PyEmail-0.0.1
You are using pip version 9.0.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

pip3 install ipdb
Collecting ipdb
  Downloading https://files.pythonhosted.org/packages/80/fe/4564de08f174f3846364b3add8426d14cebee228f741c27e702b2877e85b/ipdb-0.11.tar.gz
Requirement already satisfied: setuptools in /usr/local/python3/lib/python3.8.1/site-packages (from ipdb)
Collecting ipython>=5.0.0 (from ipdb)
  Downloading https://files.pythonhosted.org/packages/b1/7f/91d50f28af3e3a24342561983a7857e399ce24093876e6970b986a0b6677/ipython-6.4.0-py3-none-any.whl (750kB)
    62% |████████████████████            | 471kB 54kB/s eta 0:00:06
好一会下载安装就能装上这个,但是提示：You are using pip version 9.0.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
ln -s /usr/local/python3/bin/pip3 /usr/bin/pip
pip install --upgrade pip

pip install ipdb   #再一次安装这个Python的调试扩展
python -m pdb mail.py

最后，这些脚本总结起来放一块就这些，方便后期再安装之用：
tar zxvf Python-3.8.1.tgz -C /opt/ cd /opt/Python-3.8.1/   ./configure --prefix=/usr/local/python3 yum install zlib zlib-devel -y make && make install   ln -s /usr/local/python3/bin/python3.8.1 /usr/bin/python3 ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3 mv /usr/bin/pip{,.backup} ln -s /usr/local/python3/bin/pip3 /usr/bin/pip mv /usr/bin/python{,.backup} ln -s /usr/local/python3/bin/python3.8.1 /usr/bin/python sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-builddep sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-config-manager sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-debug-dump sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-debug-restore sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yumdownloader sed -i 's/#!\/usr\/bin\/python /#!\/usr\/bin\/python2.7 /' /usr/bin/yum-groups-manager sed -i 's/#!\/usr\/bin\/python$/#!\/usr\/bin\/python2.7/' /usr/bin/yum sed -i 's/#!\/usr\/bin\/python$/#!\/usr\/bin\/python2.7/' /usr/libexec/urlgrabber-ext-down

来自：https://blog.csdn.net/hobohero/article/details/54381475
来自：https://blog.csdn.net/wjqwinn/article/details/75633714

作者：jackxiang@向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
地址：https://jackxiang.com/post/9795/
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