ubuntu切换不同版本的python

有时候编译安卓或者SDK代码，如果报错，表示 Python 的替代版本尚未被update-alternatives 命令识别，此时需要切换到对应的版本才能正常编译。比如我在编译内核的时候出现了以下报错：

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  CC      security/selinux/netif.o
  CC      net/netfilter/core.o
  CC      lib/percpu_ida.o
  CC      net/llc/llc_input.o
  CC      drivers/base/driver.o
  CC      net/netfilter/nf_log.o
  CC      net/netfilter/nf_queue.o
Traceback (most recent call last):^C
Traceback (most recent call last):
  File "./scripts/gcc-wrapper.py", line 107, in <module>
  File "./scripts/gcc-wrapper.py", line 107, in <module>
Traceback (most recent call last):
Traceback (most recent call last):
Traceback (most recent call last):
  File "./scripts/gcc-wrapper.py", line 107, in <module>
  File "./scripts/gcc-wrapper.py", line 107, in <module>
Traceback (most recent call last):
Traceback (most recent call last):
  File "./scripts/gcc-wrapper.py", line 107, in <module>
Traceback (most recent call last):
    status = run_gcc()
  File "./scripts/gcc-wrapper.py", line 107, in <module>
  File "./scripts/gcc-wrapper.py", line 107, in <module>
  File "./scripts/gcc-wrapper.py", line 91, in run_gcc
Traceback (most recent call last):
Traceback (most recent call last):
  File "./scripts/gcc-wrapper.py", line 107, in <module>
    status = run_gcc()
    status = run_gcc()
  File "./scripts/gcc-wrapper.py", line 91, in run_gcc
Traceback (most recent call last):
      File "./scripts/gcc-wrapper.py", line 91, in run_gcc
status = run_gcc()
      File "./scripts/gcc-wrapper.py", line 107, in <module>
status = run_gcc()
  File "./scripts/gcc-wrapper.py", line 91, in run_gcc
      File "./scripts/gcc-wrapper.py", line 91, in run_gcc
status = run_gcc()

目前常用的python版本是3.8和2.7版本，可以通过 python --version 命令查看你当前的系统使用是哪个版本。

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caizd@drivers:~$ python --version
Python 2.7.17

sudo update-alternatives --list python 查看当前安装的所有Python版本：

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caizd@drivers:~/rk3399_linux/rk3399_linux$ sudo update-alternatives --list python
/usr/bin/python2.7
/usr/bin/python3.8

如果出现报错表示 Python 的替代版本尚未被update-alternatives 命令识别到，此时需要执行命令安装一下。输入注意后面的1、2序号

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update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1  
update-alternatives --install /usr/bin/python python /usr/bin/python3.8 2

如果要切换python版本，使用 update-alternatives --config python命令，然后输入对应的数字,选择版本即可。

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caizd@drivers:~$ update-alternatives --config python
There are 2 choices for the alternative python (providing /usr/bin/python).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /usr/bin/python2.7   1         auto mode
* 1            /usr/bin/python2.7   1         manual mode
  2            /usr/bin/python3.8   1         manual mode

Press <enter> to keep the current choice[*], or type selection number: 1