【发布时间】：2017-08-21 02:48:29
【问题描述】：
前几天我决定让命令 python 默认启动 python3 而不是 python2。
所以我这样做了：
$ sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 2
$ sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.5 3
$ sudo update-alternatives --config python
$ sudo update-alternatives --config python
There are 2 choices for the alternative python (providing /usr/bin/python).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/python3.5 3 auto mode
1 /usr/bin/python2.7 2 manual mode
2 /usr/bin/python3.5 3 manual mode
Press <enter> to keep the current choice[*], or type selection number: 0
这一切都奏效了。伟大的！ :)
$ python -V
Python 3.5.2
但不久之后，我意识到在安装和删除 python 包时我已经破坏了 apt/aptitude，因为 apt 期望它发生了 python2。
事情就是这样。
$ sudo apt remove python-samba
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
samba-libs
Use 'sudo apt autoremove' to remove it.
The following packages will be REMOVED:
python-samba
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 5,790 kB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 187285 files and directories currently installed.)
Removing python-samba (2:4.3.11+dfsg-0ubuntu0.16.04.5) ...
File "/usr/bin/pyclean", line 63
except (IOError, OSError), e:
^
SyntaxError: invalid syntax
dpkg: error processing package python-samba (--remove):
subprocess installed pre-removal script returned error exit status 1
Traceback (most recent call last):
File "/usr/bin/pycompile", line 35, in <module>
from debpython.version import SUPPORTED, debsorted, vrepr, \
File "/usr/share/python/debpython/version.py", line 24, in <module>
from ConfigParser import SafeConfigParser
ImportError: No module named 'ConfigParser'
dpkg: error while cleaning up:
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
python-samba
E: Sub-process /usr/bin/dpkg returned an error code (1)
最终我猜它希望 python2 作为默认值，所以我取消了我的更改如下：
$ sudo update-alternatives --config python
There are 2 choices for the alternative python (providing /usr/bin/python).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/bin/python3.5 3 auto mode
1 /usr/bin/python2.7 2 manual mode
2 /usr/bin/python3.5 3 manual mode
Press <enter> to keep the current choice[*], or type selection number: 1
$ python -V
Python 2.7.12
然后 apt 再次工作
$ sudo apt remove python-samba
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
samba-libs
Use 'sudo apt autoremove' to remove it.
The following packages will be REMOVED:
python-samba
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 5,790 kB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 187285 files and directories currently installed.)
Removing python-samba (2:4.3.11+dfsg-0ubuntu0.16.04.5) ...
所以我不得不让它默认为 python 2，但我在 python 3 中开发，所以希望我的系统在我运行 python 和空闲时默认为 python 3。
谁能告诉我如何在不破坏 apt 的情况下实现这一目标？
我的系统是运行 Ubuntu 的 Raspberry Pi 3B：
Linux mymachine 4.4.38-v7+ #938 SMP Thu Dec 15 15:22:21 GMT 2016 armv7l armv7l armv7l GNU/Linux
（其实是arm v8）
$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.2 LTS"
【问题讨论】：
-
离开
python指向 python2 否则你会遇到很多的麻烦 -
是的，谢谢，我也这么想。 :)
-
这个问题的答案需要更新。我目前正在运行默认使用 python3 的 Debian（通过 update-alternatives），我没有遇到任何问题。如果将来出现问题，我会发表评论，但趋势是它将成为新的默认值。
标签： python linux ubuntu debian apt