batch file to check if Python is installed

Question

I've written a batch script that checks if Python is installed, if it's not installed - it initiates the Python installer contained in the same folder as itself.

I'm using the following code:

reg query "hkcu\software\Python 2.6"

if ERRORLEVEL 1 GOTO NOPYTHON 

:NOPYTHON
ActivePython-2.6.4.8-win32-x86.msi

reg query "hklm\SOFTWARE\ActiveState\ActivePerl\" 1>>Output_%date%_%time%.log 2>&1
if ERRORLEVEL 1 GOTO NOPERL 

reg query "hklm\SOFTWARE\Gtk+"
if ERRORLEVEL 1 GOTO NOPYGTK 


:NOPERL
ActivePerl-5.10.1.1006-MSWin32-x86-291086.msi 1>>Output_%date%_%time%.log 2>&1

:NOPYGTK
pygtk_windows_installer.exe

But in some cases the installer starts up even if Python is installed. What is the problem here?

Answer 1

For those who just want a simple check if Python is installed and can be executed without going into the registy, in your batch file:

:: Check for Python Installation
python --version 2>NUL
if errorlevel 1 goto errorNoPython

:: Reaching here means Python is installed.
:: Execute stuff...

:: Once done, exit the batch file -- skips executing the errorNoPython section
goto:eof

:errorNoPython
echo.
echo Error^: Python not installed

Answer 2

Your code doesn't branch after the registry query is done. No matter what the first if ERRORLEVEL evaluates to, the next step is always to step into the :NOPYTHON label.

Ed: Here is an example how to make it work. The idea is to add another goto statement which will skip the :NOPYTHON label if desired.

reg query "hkcu\software\Python 2.6"  
if ERRORLEVEL 1 GOTO NOPYTHON  
goto :HASPYTHON  
:NOPYTHON  
ActivePython-2.6.4.8-win32-x86.msi  

:HASPYTHON  
reg query "hklm\SOFTWARE\ActiveState\ActivePerl\" 1>>Output_%date%_%time%.log 2>&1