running Python2 Python3 parallel concurrent

Wed Mar 30 21:05:46 EDT 2011

Greetings,

     The purpose of this communique is to document a process for 
installing python2.7.1 in parallel with python3.2 on a concurrent 
desktop with independent idle and python path structure.

     Each version (python2, python3) will be installed in a separate 
python shell (idle) run on a separate local install so that both 
versions are running side-by-side on the same user desktop, each python 
shell having a unique .idlerc(v) configuration dir for look&feel as well 
as separate recent files lists and separate working .py folders.

     Neither of the installs should affect the other installation (nor 
idle operation), nor should the installs affect the system-wide default 
install (python2.6.2 in my case running ubuntu 9.04 jaunty). As well, 
the search paths should not overlap except at the top $HOME level. The 
over-all purpose is to be able to play with both versions together in 
order to facilitate/enable/solve concurrent development, migration, and 
debug issues between the two versions.

     I trust that if the community has already solved this problem, and 
has a better way, that I may discover it and be able to adopt it to my 
own environment as well.

     If you find any mistakes, please let me know.

             Best regards, m harris.

     The primary unordered issues for solution(s) are:

     1) separate PythonX folders for .py files, $HOME/PythonX
     2) separate desktop launchers to cleanly launch idleX for pythonX
     3) separate .idlercX files in the home dir for IDLE pythonX
     4) separate correct $HOME/local/pythonX installation folders
     5) separate correct $HOME/bin/ launch scripts and sym links
     6) Config from sources with correct --prefix setting
     7) Local Build & Install

===========================================================
BUILD VERSIONS FROM SOURCE
===========================================================
     Download the 2.7.1 and 3.2 tarballs from here:

     http://www.python.org/download/

     From your $HOME directory create the modules (.py) folder with:

         mkdir Python3             ie.,  $HOME/Python3/

     .... and then create the local installation folder in $HOME/local:

         mkdir local
         cd local
         mkdir python3             ie.,  $HOME/local/python3/

     Create a $HOME/bin/ folder, if it does not already exist.

     Unpack each tarball in $HOME with:

         tar -xvf Python-3.2.tar.bz2 --bzip2

     cd Python-3.2    and then build & install with:

         ./configure --prefix=$HOME/local/python3
         make
         make install

     NOTES:  Repeat these steps for each local version. It is important 
that the development headers already be installed, including the tk-dev 
package so that tkinter mod will get built enabling idle. The tarballs 
are available in several compression schemes... I chose bzip2.
     The --prefix option tells the installer where pythonX will live; 
this will be a local install visible only to the development user.

===========================================================
Symbolic link(s)
===========================================================

     Create a symbolic link for python in $HOME/bin/ with:

     cd $HOME/bin/
     ln -sf $HOME/local/python3/bin/python3 python3

     note:  (python3 can now be invoked from a linux terminal)

            Repeat the steps for each version.

            You may need to set your linux path to include
            $HOME/bin/  in either .profile or .bashrc if not
            already in place. This is usually already set on
            most modern linux distros if ~/bin/ exists.

===========================================================
Launcher Scripts
===========================================================

     Create the bash launcher script used for setting the
     PYTHONPATH and starting the python3 script. Use a text
     editor of your choice to create a text file in $HOME/bin/
     called  Python3-IDE  containing these three lines:

#!/bin/sh
export PYTHONPATH=$HOME/Python3
exec $HOME/bin/idle-python3 -n

     Now, create the python script for importing and launching
     the PyShell from idlelib; use a text editor to create a
     text file in $HOME/bin/ called  idle-python3  containing:

#!/home/<username>/bin/python3

from idlelib.PyShell import main
if __name__ == '__main__':
     main()

     The first line /home/<username>/ is $HOME, but may have to
     be spelled out in the script above. Now, set both scripts
     executeable with:

         chmod 0754 $HOME/bin/Python3-IDE
         chmod 0754 $HOME/bin/idle-python3

     Notes:  Repeat for each version. Summary; each version will
     have its own launcher script ( PythonX-IDE ) and each will
     have its own python idle starter script ( idle-pythonX ).

     The launcher script is the 'called' file from the Desktop
     launcher icon, which sets the PYTHONPATH. The python idle
     starter script correctly starts the interpreter and then
     initiates the PyShell (python idle shell) import main and
     run.

===========================================================
IDLE Configuration File   .idlrcX
===========================================================

     By default the  idlelib.configHandler  sets the config
     dir to  $HOME/.idlerc   (we will change this so that
     each idle version will have its own config directory
     in $HOME).  The cfgDir attribute is held in the config
     handler in the following module hierarchy:

[module] idlelib.configHandler

     Class IdleConf

         def GetUserCfgDir()

             cfgDir='.idlerc'

     Use a text editor and "carefully" change the config
     handler located here:

         $HOME/local/python3/lib/python3.2/idlelib/configHandler.py

     (you might want to backup the configHandler.py file just in
      case you honk it somehow...    )         :-)

     Find the Class IdleConf and then locate the def called:
         GetUserCfgDir()

     Change the attribute cfgDir to:
         cfgDir='.idlerc3'

     Save the file.

     Notes:  Repeat for each version.  Summary, each version will
     have its own .idlercX configuration file:

         .idlerc3
         .idlerc2

     Also, the default python installation will still have its own
     configuration file  .idlerc  specific to the system-wide IDLE
     config.

===========================================================
Construct Desktop Launchers
===========================================================

     Build each Desktop python application launcher in the
     usual way, and point the lancher to  $HOME/bin/Python3-IDE

     Repeat this step for each version application launcher.

===========================================================
DONE   enjoy a cup of tea
===========================================================

     At this point you should be able to launch each python version in 
its own python shell from the Desktop and have them both running 
concurrently side-by-side without stepping on one anothers toes, as it 
were, and each having its own environment look & feel.

     I actually set one of the shells to have differing colors and font 
so that I can visually remember which environment I'm coding to. Also, I 
keep my python3.py files only in Python3 and my python2.py files only in 
Python2. In this way they can have the same names exactly but because 
the path structures are completely isolated the correct .py is imported 
depending on the version environment.

     Kind regards,

     m harris
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