If you want to not infect your current shell with the new environment, you can just run it in a subshell by using parentheses:

    $ ( . /full_path/env/bin/activate && python myapp.py --workers=3 )

This works for anything that you'd like a temporary shell for:

    $ pwd
    /home/me

    $ ( cd /tmp; pwd )
    /tmp

    $ pwd
    /home/me