$ sudo apt-get update
$ sudo apt-get install python-sqlalchemy-ext 

python-sqlalchemy-ext is installed in your system.

Make ensure the python-sqlalchemy-ext package were installed using the commands given below,

$ sudo dpkg-query -l | grep python-sqlalchemy-ext *

You will get with python-sqlalchemy-ext package name, version, architecture and description in a table

python-sqlalchemy-ext package basic information: