For this type of issues in ubuntu we have to follow two points.
1. If python is not installed in server ,Install it by using below command and check Again.
apt-get install python3
2. If python is installed and still you are facing same issue means ,first you need to check python path with below command
whereis python3
Then make short link as shown below
sudo ln -s /usr/bin/python3 /usr/bin/python