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之前为了升级centos 7的版本从python2升级到python3，曾经设法只保留python3版本，删除centos中的python2版本，事实证明踩了很多坑，甚至是把linux系统搞崩溃。吓得我瑟瑟发抖。于是才发现这两个版本是可以共存的只要让对应的/usr/bin/python对应相应的机器自带python2版本，/usr/bin/python3软连接/usr/bin/python3.6,就可以通过python3指令执行python3版本。
[root@hw007 bin]# python
Python 2.7.5 (default, Oct 30 2018, 23:45:53)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
------------------------------------------------------------------------[root@hw007 bin]# python3
Python 3.6.6 (default, Mar 29 2019, 00:03:27)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
简直是非常nice，但是对于python2对应的pip和python3对应的pip有所不同。python3对应的pip是pip3。所以需要再下载一个相应的版本才行。下面是具体操作：
wget –no-check-certificate https://pypi.python.org/packages/source/s/setuptools/setuptools-19.6.tar.gz#md5=c607dd118eae682c44ed146367a17e6
tar -zxvf setuptools-19.6.tar.gz
cd setuptools-19.6/
python3 setup.py build
python3 setup.py install
wget –no-check-certificate https://pypi.python.org/packages/source/p/pip/pip-8.0.2.tar.gz#md5=3a73c4188f8dbad6a1e6f6d44d117eeb
tar -zxvf pip-8.0.2.tar.gz
cd pip-8.0.2/
python3 setup.py build
python3 setup.py install
whereis pip3 #会发现在/usr/bin中没有pip3，因此需要创建一个软连接
sudo ln -sf /usr/local/bin/pip3.6 /usr/bin/pip3 #软连接
pip3显示下面内容显示已经成功，（如果不执行软连接那步会报错：-bash: /usr/bin/pip3: No such file or directory）
Usage:
pip3 <command> [options]
Commands:
install Install packages.
download Download packages.
uninstall Uninstall packages.
freeze Output installed packages in requirements format.
list List installed packages.
show Show information about installed packages.
check Verify installed packages have compatible dependencies.
config Manage local and global configuration.
search Search PyPI for packages.
wheel Build wheels from your requirements.
hash Compute hashes of package archives.
completion A helper command used for command completion.
help Show help for commands.
General Options:
-h, --help Show help.
--isolated Run pip in an isolated mode, ignoring environment variables and user configuration.
-v, --verbose Give more output. Option is additive, and can be used up to 3 times.
-V, --version Show version and exit.
-q, --quiet Give less output. Option is additive, and can be used up to 3 times (corresponding to WARNING, ERROR, and CRITICAL logging
levels).
--log <path> Path to a verbose appending log.
--proxy <proxy> Specify a proxy in the form [user:passwd@]proxy.server:port.
--retries <retries> Maximum number of retries each connection should attempt (default 5 times).
--timeout <sec> Set the socket timeout (default 15 seconds).
--exists-action <action> Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort).
--trusted-host <hostname> Mark this host as trusted, even though it does not have valid or any HTTPS.
--cert <path> Path to alternate CA bundle.
--client-cert <path> Path to SSL client certificate, a single file containing the private key and the certificate in PEM format.
--cache-dir <dir> Store the cache data in <dir>.
--no-cache-dir Disable the cache.
--disable-pip-version-check
Don't periodically check PyPI to determine whether a new version of pip is available for download. Implied with --no-index.
--no-color Suppress colored output然后我执行pip3进行下载：
pip3 install paddlepaddle会报错，显示当前pip版本太低，需要执行以下指令，然后在执行上面指令：
pip3 install --upgrade pip
sudo ln -sf /usr/local/bin/pip3.6 /usr/bin/pip3
pip3 install paddlepaddle