要在Raspbian GNU / Linux上更改为默认Python版本，
首先列出所有可用的Python版本：

# ls /usr/bin/python*
/usr/bin/python  /usr/bin/python2  /usr/bin/python2.7  /usr/bin/python3  /usr/bin/python3.2  /usr/bin/python3.2mu  /usr/bin/python3mu

设置备选方案：

# update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
update-alternatives: using /usr/bin/python2.7 to provide /usr/bin/python (python) in auto mode
# update-alternatives --install /usr/bin/python python /usr/bin/python3.2 2
update-alternatives: using /usr/bin/python3.2 to provide /usr/bin/python (python) in auto mode

由于我们已将“python3.2”设置为更高的优先级，因此它现在应该是您的默认设置：

# python --version
Python 3.2.3

要在python版本之间切换，使用“update-alternatives”命令：

# update-alternatives --config python
There are 2 choices for the alternative python (providing /usr/bin/python).
  Selection    Path                Priority   Status
-----------------------------------------------------------
* 0            /usr/bin/python3.2   2         auto mode
  1            /usr/bin/python2.7   1         bananaal mode
  2            /usr/bin/python3.2   2         bananaal mode
Press enter to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/bin/python2.7 to provide /usr/bin/python (python) in bananaal mode

查看新的默认版本：

# python --version
Python 2.7.3