同时装了Python3和Python2，怎么用pip？
Ubuntu13.04, 系统内同时装了Python3.3 和 2.7
用sudo apt-get install python-pip
sudo apt-get install python3-pip
分别装了两个版本对应的pip
但是现在运行pip install 只能给2.7版安装库（好像是因为重名只能调用python-pip），怎么样设置才能给3.3版安装呢？
回复内容：
python3的用pip3 pip，pip2，pip3 对于Linuxpy -2 -m pip install sth，py -3 -m pip install sth 对于Windows 详见官方文档
https://docs.python.org/3/installing/ mac自带py2.7，自己安装了pip
想学习Python3，但是暂时又离不开Python2。在Windows上如何让它们共存呢？
目前国内网站经常会让大家把其中一个python.exe改个名字（嗯，我也这样讲过，在此纠正一下），这样区分开两个可执行文件的名字，但是这样做有一个重大的隐患，就是修改了名字的那个python对应的pip将无法使用。
官方的解法是什么？
事实上这个问题几年以前Python社区就给出了官方解决方案，只不过国内一直没有注意到罢了。
我们在安装Python3（>=3.3）时，Python的安装包实际上在系统中安装了一个启动器py.exe，默认放置在文件夹C:\Windows\下面。这个启动器允许我们指定使用Python2还是Python3来运行代码（当然前提是你已经成功安装了Python2和Python3）。
有关Python2和3的安装，可以参见Python部落(http://python.freelycode.com)-->影音学堂-->《0基础1小时,Python入门》的第一节。
如果你有一个Python文件叫 hello.py，那么你可以这样用Python2运行它
py -2 hello.py
类似的，如果你想用Python3运行它，就这样
py -3 hello.py
去掉参数 -2/-3
每次运行都要加入参数-2/-3还是比较麻烦，所以py.exe这个启动器允许你在代码中加入说明，表明这个文件应该是由python2解释运行，还是由python3解释运行。说明的方法是在代码文件的最开始加入一行
#! python2
或者
#! python3
分别表示该代码文件使用Python2或者Python3解释运行。这样，运行的时候你的命令就可以简化为
py hello.py
使用pip
当Python2和Python3同时存在于windows上时，它们对应的pip都叫pip.exe，所以不能够直接使用 pip install 命令来安装软件包。而是要使用启动器py.exe来指定pip的版本。命令如下：
py -2 -m pip install XXXX
-2 还是表示使用 Python2，-m pip 表示运行 pip 模块，也就是运行pip命令了。如果是为Python3安装软件，那么命令类似的变成
py -3 -m pip install XXXX
#! python2 和 # coding: utf-8 哪个写在前面？
对于Python2用户还有另外一个困惑，Python2要在代码文件顶部增加一行说明，才能够在代码中使用中文。如果指明使用的Python版本也需要在文件顶部增加一行，那哪一行应该放在第一行呢？
#! python2 需要放在第一行，编码说明可以放在第二行。所以文件开头应该类似于：
#! python2
# coding: utf-8
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提供一个Windows下的解决方案：
先安好的python2的pip，它的默认路径是C:\Python27\Scripts
看到没有，它怕你找不到，自己给自己起了3个名字，随便你用哪个。
然后安装python3的pip，它的默认路径是C:\Users\***\AppData\Local\Programs\Python\Python35-32\Scripts
也是3个名字。
然后你把这两个路径填加到环境变量中，就可以愉快的用
pip2 install ... (python2)
pip3 install ... (python3)
分别安装库了。
为了回答这个问题，特意跑到一台 CentOS 6.5 上装了一个 Python3（手头没有 Ubuntu 的环境），然后又装了一个 pip，通过ln创建连接、alias创建别名这些操作，证明Python2 和 Python3 还是可以完美并存的。
题主的问题不在于能不能并存，而在于用默认的 pip install 命令给Python3 安装这个做法本身就是错误的，下面是我的解决方案：
环境上之前已经有了 Python 和 pip,
# python --version:
Python 2.7.9
# pip --version
pip 8.1.1 from /usr/local/lib/python2.7/site-packages (python 2.7)
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同上，用 virtualenv
pip: www.pip-installer.orgvirtualenv: http://www.virtualenv.orgvirtualenvwrapper: http://virtualenvwrapper.readthedocs.org
virtualenv 是 lib 级别的隔离，如果需要python解释器的隔离，可以直接用
yyuu/pyenv · GitHub
建议用yyuu/pyenv · GitHub , 这样可以在不修改系统自带的python的前提下，安装任意多个Python版本，而且版本之间是相互隔离的，多版本管理起来很方便。
用 virtualenv 是王道。
另外根据 http://packages.ubuntu.com/zh-cn/quantal/all/python3-pip/filelist 这里看，python3-pip 装出来的应该是 pip-3.2 之类。用 dpkg -L python3-pip 看一下命令全路径。
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