MS script; Python version check prelaunch of Python module

@Echo Off

REM  [email protected]
REM  2011-Oct-3

REM  This will run a python module if the version is correct.
REM  the Python version is done before any modules are run.

REM  Some benefits to this script are:
REM     no files are created; avoids file write permission issues
REM     no environment varibles are created; avoids permission issues
REM     no Python modules are run; avoids syntax exceptions between
REM         Python versions

REM Some cons are:
REM     This is a post Window 2000++ script; Win XP and later work.
REM     This is not a unix/linux script although it can be adapted.
REM     It is likely that not all Python interpreters support the
REM     the -V option or push the -V output to stderr;
REM         In which case just remove 2>&1
REM     Assumes the output to be formatted like "Python x.y"
REM     You have to run this script every time to launch your Python
REM         app to benefit from this check.
REM         So therefore you need to include it in your distribution

REM  http://www.fpschultze.de/modules/smartfaq/faq.php?faqid=17
REM  Read on 2011-Oct-3

REM  Try this at Windows/DOS command prompt to see:
REM     python.exe -V

REM  This should send a string like "Python 2.7" without quotation marks,
REM  to stderr (prints to console)

REM  If your python.exe version doesn't support the -V option
REM  this batch will still work.

REM  This is not Python.
REM  GENERALLY use " (double qoutes) in Windows DOS scripts/batch files.
REM  Do not use ' (single quotes) unless the DOS command supports it

REM  I only had one version of Python.exe on my system.
REM  I don't know what text other versions of "python.exe -V" will return.

REM  My version returns "Python 2.7" without the quotes,
REM  even though I have version 2.7.0

REM  Perhaps other people with other versions of Python can post what
REM  their version of "python.exe -V" returns textually. I could then
REM  update MS-Windows XP script.

REM  Versions of Microsoft Windows OSes after MS-Windows XP Pro
REM  will likely run this script fine.
REM  It is very likely this script can be converted to a linux version.

REM alternate: python -c "import sys; print sys.version_info" > pyver.txt

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.7" > Nul
If Not ErrorLevel 1 Goto Python27

REM  Here is the break down of that DOS line
    REM  "FOR /F", "IN", "DO", "ECHO" are internal DOS commands; ie part of cmd.exe

    REM  "tokens=1,2"
    REM     is a paramater for the "FOR /F" DOS command.
    REM     It implicidly means "tokens=1,2 delims= "

    REM     "delims= " means break down the string at every space character.
    REM     So a string like "Python 2.7" will be broken down into:
    REM     "Python" and "2.7"
    REM     "delims" means delimiter

    REM  "tokens=1,2" %%G
    REM     means grab the "word zero" and grab "word one"
    REM     in the string and put "word zero" (ie token 1) into variable
    REM     %%G and "word one" (ie token 2) into variable %%H.

    REM     Where did %%H come from?
    REM     For each token in string, create a script varaible starting
    REM     with %%G as the first varible name.
    REM     This is an implicid feature of "FOR /F";
    REM     max is 26 %%A-%%Z.

    REM  IN
    REM     means: in the string returned by the following -thing-

    REM  q:\python27\python.exe -V
    REM     tells python.exe to use the -V argument;
    REM     which means print out the Python version
    REM     to stderr and then exit (python.exe)

    REM  2>&1
    REM     means to tell the comand to redirect whatever is sent
    REM     to stderr to stdout.

    REM     In Lunix you could use just  2>&  I believe
    REM     python.exe -V prints the version to stderr, not stdout.
    REM     So this needs to be redirected to stdout to make it
    REM     a string that can be used by a DOS SCRIPT

    REM "python.exe -V 2>&1"
    REM     The double quotation marks are needed
    REM     because there are command parameters seperated by spaces
    REM     and redirection, stderr to stdout, in the command

    REM (' ..."python.exe.."  ')
    REM     The parenthesis and single quotes tell the "FOR /F" command
    REM     to execute the string as if the user typed it at the
    REM     command prompt' and from that output of that execution
    REM     put that output into a string usable by the "FOR /F" command.

    REM DO
    REM     "DO" is part of the "FOR /F" command

    REM ECHO %%H
    REM     write %%H to stdout; not that it is not %%G which would
    REM     normally be the string "Python"

    REM | find "2.7" > Nul
    REM     | == pipe
    REM     find "2.7"
    REM        is a DOS command that will search for a string "2.7"
    REM        note the double quotes, no single quotes
    REM        so pipe a string into find and compare to "2.7"
    REM        and MOST importantly if it matches return with an
    REM        Errorlevel of 1 if there is a match
    REM    > Nul
    REM        and send the search results, ie the output (not exit code)
    REM        to the nul device instead of stderr or stdout.
    REM        The user doesn't need to see that.

    REM If Not ErrorLevel 1 Goto Python27
    REM    means if "find"'s exit code is 1 then jump to the script
    REM    section labeld Python27.
    REM    A DOS lable is aline that starts with :<text>

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.4" > Nul
If Not ErrorLevel 1 Goto Python24

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.5" > Nul
If Not ErrorLevel 1 Goto Python25

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.6" > Nul
If Not ErrorLevel 1 Goto Python26

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.7" > Nul
If Not ErrorLevel 1 Goto Python27

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.8" > Nul
If Not ErrorLevel 1 Goto Python28

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "2.9" > Nul
If Not ErrorLevel 1 Goto Python29

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "3.0" > Nul
If Not ErrorLevel 1 Goto Python30

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "3.1" > Nul
If Not ErrorLevel 1 Goto Python31

FOR /F "tokens=1,2" %%G IN ('"python.exe -V 2>&1"') DO ECHO %%H | find "3.2" > Nul
If Not ErrorLevel 1 Goto Python32

Goto :EOF

REM  ------------------------------------
::Python 2.4 code
 :Python24
 echo FOUND 2.4
 python.exe my_python_app24.py
 goto :EOF

::Python 2.5 code
 :Python25
 echo FOUND 2.5
 python.exe my_python_app25.py
 goto :EOF

::Python 2.6 code
 :Python26
 echo FOUND 2.6
 python.exe my_python_app26.py
 goto :EOF

::Python 2.7 code
 :Python27
 echo FOUND 2.7
 python.exe my_python_app27.py
 goto :EOF

:: Python 2.8
 :Python28
 echo Python 2.8 found
 python.exe my_python_app28.py
 goto :EOF

:: Python 2.9; doesn't exist yet
 :Python29
 echo Python 2.9 found
 python.exe my_python_app29.py
 goto :EOF

:: Python 3.0
 :Python30
 echo Python 3.0 found
 python.exe my_python_app30.py
 goto :EOF

:: Python 3.1
 :Python31
 echo Python 3.1 found
 python.exe my_python_app31.py
 goto :EOF

:: Python 3.2
 :Python32
 echo Python 3.2 found
 python.exe my_python_app32.py
 goto :EOF

::EOF
:EOF