Change the default Python version of Ubuntu

Which version of Python First of all there is to see in the system

Python version you want to modify a specific user, only need to create an alias (alias) can be in their home directory. Open ~ / .bashrc file for the user, add a new alias information to modify the default version of Python used.
```
alias python='/usr/bin/python3.6'
```
Once done, log in again or reload the .bashrc file, make the operation effective.
```
. ~/.bashrc
```

Use update-alternatives to change the version of Python for the entire system. Log in as root, first proceed to list all of the available python alternative version information:
```
update-alternatives --list python
```

update-alternatives: error: no alternatives for python

If the error message shown above appears, the alternative versions of the Python command update-alternatives have not been identified. Want to solve this problem, we need to update the look instead of a list, will python2.7 and python3.6 in it.

update-alternatives --install /usr/bin/python python /usr/bin/python2.7

update-alternatives --install /usr/bin/python python /usr/bin/python3.6

--install option uses a number of parameters to create a symbolic link. The last parameter specifies the priority of this option, if we do not have to manually set up an alternative option, the option with the highest priority will be selected. In this example, we set the priority /usr/bin/python3.6 2, the update-alternatives command will automatically set it as the default version of Python.
```
python --version
```
At this time, check the version already python 3.6

update-alternatives --list python

/usr/bin/python2.7
/usr/bin/python3.6

Now, we can use the command below at any time in Python alternative versions listed in any switched.
```
update-alternatives --config python
```

Once a Python alternative versions of our system no longer exists, we can be removed from the list of update-alternatives. For example, we can release the list of removed python2.7 out.

update-alternatives --remove python /usr/bin/python2.7

rm -rf /data/logs
 

ln -s /temp/logs /data/logs