linux上有两个版本的python。如何使 2.7 成为默认值
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Two versions of python on linux. how to make 2.7 the default
提问by Anthony
I've got two versions of python on my linuxbox:
我的 linuxbox 上有两个版本的 python：
$python
Python 2.6.6 (r266:84292, Jul 10 2013, 22:48:45)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
$ /usr/local/bin/python2.7
Python 2.7.3 (default, Oct 8 2013, 15:53:09)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>>
$ which python
/usr/bin/python
$ ls -al /usr/bin/python
-rwxr-xr-x. 2 root root 4864 Jul 10 22:49 /usr/bin/python
How can I make 2.7 be the default version so when I type pythonit puts me in 2.7?
我怎样才能让 2.7 成为默认版本，所以当我输入python它时，我会进入 2.7？
采纳答案by abarnert
You probably don't actually want to change your default Python.
您可能实际上并不想更改默认的 Python。
Your distro installed a standard system Python in /usr/bin, and may have scripts that depend on this being present, and selected by #! /usr/bin/env python. You can usuallyget away with running Python 2.6 scripts in 2.7, but do you want to risk it?
您的发行版在 中安装了标准系统 Python /usr/bin，并且可能具有依赖于此的脚本，并由#! /usr/bin/env python. 您通常可以在 2.7 中运行 Python 2.6 脚本，但您想冒险吗？
On top of that, monkeying with /usr/bincan break your package manager's ability to manage packages. And changing the order of directories in your PATHwill affect a lot of other things besides Python. (In fact, it's more common to have /usr/local/binahead of /usr/bin, and it may be what you actually want—but if you have it the other way around, presumably there's a good reason for that.)
最重要的是，玩弄/usr/bin可能会破坏您的包管理器管理包的能力。并且更改目录的顺序PATH会影响除 Python 之外的许多其他内容。（事实上，更常见的是有/usr/local/bin提前/usr/bin，它可能是你真正想要的——但如果你有相反的方式，大概有一个很好的理由。）
But you don't needto change your default Python to get the system to run 2.7 when you type python.
但是，您无需更改默认 Python 即可在您键入python.
First, you can set up a shell alias:
首先，您可以设置一个shell别名：
alias python=/usr/local/bin/python2.7
Type that at a prompt, or put it in your ~/.bashrcif you want the change to be persistent, and now when youtype pythonit runs your chosen 2.7, but when some program on your system tries to run a script with /usr/bin/env pythonit runs the standard 2.6.
在提示符下输入，或者~/.bashrc如果您希望更改是持久的，则将其放入您的代码中，现在当您输入python它时会运行您选择的 2.7，但是当您系统上的某些程序尝试使用/usr/bin/env python它运行脚本时，它会运行标准的 2.6。
Alternatively, just create a virtual environmentout of your 2.7 (or separate venvs for different projects), and do your work inside the venv.
或者，只需在 2.7 中创建一个虚拟环境（或为不同项目创建单独的 venv），然后在 venv 中进行工作。
回答by Amber
Add /usr/local/binto your PATHenvironment variable, earlier in the list than /usr/bin.
添加/usr/local/bin到您的PATH环境变量中，在列表中比/usr/bin.
Generally this is done in your shell's rc file, e.g. for bash, you'd put this in .bashrc:
通常这是在你的 shell 的 rc 文件中完成的，例如对于 bash，你可以把它放在.bashrc：
export PATH="/usr/local/bin:$PATH"
This will cause your shell to look first for a pythonin /usr/local/bin, before it goes with the one in /usr/bin.
这将导致您的外壳首先查找pythonin /usr/local/bin，然后再查找in /usr/bin。
(Of course, this means you also need to have /usr/local/bin/pythonpoint to python2.7- if it doesn't already, you'll need to symlink it.)
（当然，这意味着您还需要/usr/local/bin/python指向python2.7- 如果还没有，则需要对其进行符号链接。）
回答by emesik
I guess you have installed the 2.7 version manually, while 2.6 comes from a package?
我猜你已经手动安装了 2.7 版本，而 2.6 来自一个包？
The simple answer is: uninstall python package.
简单的答案是：卸载python包。
The more complex one is: do not install manually in /usr/local. Build a package with 2.7 version and then upgrade.
更复杂的一种是：不要在/usr/local 中手动安装。构建一个 2.7 版本的包，然后升级。
Package handling depends on what distribution you use.
包处理取决于您使用的发行版。
回答by Prakash Kamath
All OS comes with a default version of python and it resides in /usr/bin. All scripts that come with the OS (e.g. yum) point this version of python residing in /usr/bin. When you want to install a new version of python you do not want to break the existing scripts which may not work with new version of python.
所有操作系统都带有默认版本的 python，它驻留在 /usr/bin 中。操作系统附带的所有脚本（例如 yum）都指向此版本的 python 驻留在 /usr/bin 中。当您想安装新版本的 python 时，您不想破坏可能不适用于新版本 python 的现有脚本。
The right way of doing this is to install the python as an alternate version.
正确的做法是安装 python 作为替代版本。
e.g.
wget http://www.python.org/ftp/python/2.7.3/Python-2.7.3.tar.bz2
tar xf Python-2.7.3.tar.bz2
cd Python-2.7.3
./configure --prefix=/usr/local/
make && make altinstall
Now by doing this the existing scripts like yum still work with /usr/bin/python. and your default python version would be the one installed in /usr/local/bin. i.e. when you type python you would get 2.7.3
现在通过这样做，像 yum 这样的现有脚本仍然可以与 /usr/bin/python 一起使用。您的默认 python 版本将是安装在 /usr/local/bin 中的版本。即当你输入 python 你会得到 2.7.3
This happens because. $PATH variable has /usr/local/bin before usr/bin.
发生这种情况是因为。$PATH 变量在 usr/bin 之前有 /usr/local/bin。
/usr/lib64/qt-3.3/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
If python2.7 still does not take effect as the default python version you would need to do
如果python2.7仍然没有作为默认的python版本生效，你需要做
export PATH="/usr/lib64/qt-3.3/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"
回答by Sreenath
Enter the command
输入命令
which python
//output:
/usr/bin/python
cd /usr/bin
ls -l
Here you can see something like this
在这里你可以看到这样的东西
lrwxrwxrwx 1 root root 9 Mar 7 17:04 python -> python2.7
your default python2.7 is soft linked to the text 'python'
您的默认 python2.7 软链接到文本“python”
So remove the softlink python
所以删除软链接python
sudo rm -r python
then retry the above command
然后重试上面的命令
ls -l
you can see the softlink is removed
你可以看到软链接被删除了
-rwxr-xr-x 1 root root 3670448 Nov 12 20:01 python2.7
Then create a new softlink for python3.6
然后为python3.6新建一个软链接
ln -s /usr/bin/python3.6 python
ln -s /usr/bin/python3.6 python
Then try the command pythonin terminal
然后python在终端中尝试命令
//output:
Python 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0] on linux
Type help, copyright, creditsor licensefor more information.
类型help，copyright，credits或license了解更多信息。
回答by Shiv Buyya
Verify current version of python by:
通过以下方式验证 python 的当前版本：
$ python --version
then check python is symbolic link to which file.
然后检查python是哪个文件的符号链接。
$ ll /usr/bin/python
Output Ex:
输出示例：
lrwxrwxrwx 1 root root 9 Jun 16 2014 /usr/bin/python -> python2.7*
Check other available versions of python:
检查其他可用版本的python：
$ ls /usr/bin/python*
Output Ex:
输出示例：
/usr/bin/python /usr/bin/python2.7-config /usr/bin/python3.4 /usr/bin/python3.4m-config /usr/bin/python3.6m /usr/bin/python3m
/usr/bin/python2 /usr/bin/python2-config /usr/bin/python3.4-config /usr/bin/python3.6 /usr/bin/python3.6m-config /usr/bin/python3m-config
/usr/bin/python2.7 /usr/bin/python3 /usr/bin/python3.4m /usr/bin/python3.6-config /usr/bin/python3-config /usr/bin/python-config
If want to change current version of python to 3.6 version edit file ~/.bashrc:
如果要将当前版本的 python 更改为 3.6 版本，请编辑文件 ~/.bashrc：
vim ~/.bashrc
add below line in the end of file and save:
在文件末尾添加以下行并保存：
alias python=/usr/local/bin/python3.6
To install pip for python 3.6
为 python 3.6 安装 pip
$ sudo apt-get install python3.6 python3.6-dev
$ sudo curl https://bootstrap.pypa.io/ez_setup.py -o - | sudo python3.6
$ sudo easy_install pip
On Success, check current version of pip:
成功后，检查 pip 的当前版本：
$ pip3 -V
Output Ex:
输出示例：
pip 1.5.4 from /usr/lib/python3/dist-packages (python 3.6)
