How to install plpythonu extension on postgresql 9.3 ubuntu

I had Postgresql 9.3 server on ubuntu but

create extension plpythonu

      

        
        
        
      

    

crash:

ERROR: could not open extension control file "/usr/share/postgresql/9.1/extension/plpythonu.control": No such file or directory

      

        
        
        
      

    

SQL State: 58P01

Postgresql is installed using the ubuntu package management system

sudo apt-get install ...

      

        
        
        
      

    

output

SELECT * FROM pg_language;

      

        
        
        
      

    

is an

internal, c, sql, plpgsql

      

        
        
        
      

    

How can I extend postgresql so that I can use python?