Many Python scripts start with the following line::

    #!/usr/bin/env python

On UNIX-like systems, this instructs the operating system to find the ``python`` executable according to the environment. To determine which version of Python gets run, just make sure that your ``PATH`` environment variable is set up correctly.

If Python 2.0 is installed as ``/usr/local/bin/python`` and Python 1.5.2 is installed as ``/usr/bin/python``, and you want to run Python 2.0, then you should make sure that ``/usr/local/bin`` appears on your "path" before ``/usr/bin``. How and when this is done depends a lot on your system and how you want to work.

Setting the Default Environment
-------------------------------

Let's say you want to always use Python 2.0 as a particular user. This
means that you need to edit your shell's resource file so that when it
is started, it puts the directory in which Python 2.0 is found before
the directory in which Python 1.5.2 is found.

Check your system documentation for details of which file you should
edit and how you should edit it. Here's an example, though - for
``bash`` (the Bourne Again Shell), edit the ``.bashrc`` file in your
home directory and add this at the end of the file::

    export PATH=/usr/local/bin:${PATH}

This assumes that you did install Python 2.0 in ``/usr/local`` when
considering MultiplePythonVersions.

Setting the Environment for AppServer
-------------------------------------

If you just want to run AppServer with a changed environment so that
only that program uses Python 2.0, and you are running ``bash``, you
can try this::

    PATH=/usr/local/bin:${PATH} ./AppServer

Why not put this in a script::

    #!/bin/sh
    PATH=/usr/local/bin:${PATH} ./AppServer

What You Should Not Do
----------------------

Don't be tempted to go round changing the first line of all Python
scripts to something like this::

    #!/usr/bin/env python20

If you do have Python 2.0 installed as something other than ``python``
then consider making a symbolic link from another directory to the
executable, like this::

    cd /usr/local/bin
    ln -s /usr/bin/python20 python

Now add that directory (in this case, ``/usr/local/bin``) to the start
of your "path", like we did above.

-- PaulBoddie_ - 31 Oct 2001