I was trying to set default python version to python3 in Ubuntu 16.04. By default it is python2 (2.7). I followed below steps :
update-alternatives --remove python /usr/bin/python2
update-alternatives --install /usr/bin/python python /usr/bin/python3
but I'm getting the following error for the second statement,
rejeesh@rejeesh-Vostro-1015:~$ update-alternatives --install /usr/bin/python python /usr/bin/python3
update-alternatives: --install needs <link> <name> <path> <priority>
Use 'update-alternatives --help' for program usage information.
The second line mentioned can be changed to
[sudo] update-alternatives --install /usr/bin/python python /usr/bin/python3 10
This gives a priority of 10 for the path of python3.
The disadvantage of alternatively editing .bashrc is that using the commands with sudo will not work.
EDIT:
I wrote this when I was young and naive, update-alternatives is the better way to do this. See @Pardhu's answer.
Outdated answer:
Open your .bashrc file
nano ~/.bashrc. Typealias python=python3on to a new line at the top of the file then save the file with ctrl+o and close the file with ctrl+x. Then, back at your command line typesource ~/.bashrc. Now your alias should be permanent.
To change Python 3.6.8 as the default in Ubuntu 18.04 to Python 3.7.
Install Python 3.7
Steps to install Python3.7 and configure it as the default interpreter.
Install the python3.7 package using apt-get
sudo apt-get install python3.7
Add Python3.6 & Python 3.7 to update-alternatives
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 2
Update Python 3 to point to Python 3.7
sudo update-alternatives --config python3
Enter 2 for Python 3.7
Test the version of python
python3 --version
Python 3.7.1