How to write a batch file showing path to executable and version of Python handling Python scripts on Windows?
Question: It should display path to executable and version of Python for scripts run
with direct invocation of Python (`python myscript.py`) as well as for scripts
run directly (`myscript.py`). Script should not make too many assumptions on
the configuration of the system. For instance it should handle situation where
there might be no available Python.

Rationale  
I'm playing with different ways of setting environment for running Python
scripts and I thought it would be helpful to have a script telling me what the
current configuration is. I'm concerned with the standard means provided by OS
- the `PATH` environment variable and association of files' types with
handlers (`assoc` and `ftype` commands as well as `PATHEXT` environment
variable). This leaves
[pylauncher](https://bitbucket.org/vinay.sajip/pylauncher/overview) outside of
the scope of this question.


Answer: Here's my first solution:

SOLUTION 1

    
    
    @echo off
    set test_script=.pyexe.py
    rem Let's create temporary Python script which prints info we need
    echo from __future__ import print_function; import sys; print(sys.executable); print(sys.version) > %test_script%
    echo Python accessible through system PATH:
    python %test_script%
    echo ---
    echo Python set as handler for Python files:
    %test_script%
    del %test_script%
    set test_script=
    

I run into problem with this, however. When there's no valid Python
interpreter associated with Python files trying to open Python file with
`some_script.py` pops up _Open With_ system dialog. Solving this problem
requires very good knowledge of batch files. Therefore trying to come up with
a solution I've asked the following questions:

  * [How to prevent “Open With” dialog window when opening file from command window?](http://superuser.com/questions/348500/)
  * [How to escape variables with parentheses inside if-clause in a batch file?](http://stackoverflow.com/questions/7883169/)
  * [Why is delayed expansion in a batch file not working in this case?](http://stackoverflow.com/questions/7882395/)
  * [How to split double quoted strings with embedded spaces deliminated with spaces in a batch file?](http://stackoverflow.com/questions/7935308/)

Improved version of the original batch file looks now like this:

SOLUTION 1b

    
    
    @echo off
    setlocal
    set test_script=.pyexe.py
    rem Let's create temporary Python script which prints info we need
    echo from __future__ import print_function; import sys; print(sys.executable); print(sys.version) > %test_script%
    echo Python accessible through the system PATH:
    python %test_script%
    echo ---
    echo Python set as a handler for Python files:
    rem We need to check if a handler set in the registry exists to prevent "Open With"
    rem dialog box in case it doesn't exist
    rem ftype Python.File hypothetical return value:
    rem Python.File="%PYTHON_HOME%\python.exe" "%1" %*
    for /f "tokens=2 delims==" %%i in ('ftype Python.File') do set reg_entry=%%i
    rem ...now in 'reg_entry' variable we have everything after equal sign:
    rem "%PYTHON_HOME%\python.exe" "%1" %*
    set "handler="
    setlocal enableDelayedExpansion
    for %%A in (!reg_entry!) do if not defined handler endlocal & set handler=%%A
    rem ...now in 'handler' variable we have the first token:
    rem "%PYTHON_HOME%\python.exe"
    rem Now we expand any environment variables that might be present
    rem in the handler's path
    for /f "delims=" %%i in ('echo %handler%') do set expanded_handler=%%i
    if exist "!expanded_handler!" (
        "%test_script%"
    ) else (
      if not "!handler!" == "!expanded_handler!" (
        set "handler=!expanded_handler! ^(!handler!^)"
      )
      echo Handler is set to !handler! which does not exist
    )
    del %test_script%
    

This is another take avoiding problems of the above two:

SOLUTION 2

    
    
    @echo off
    setlocal
    echo Python accessible through the system PATH:
    where python
    echo ---
    echo Python set as a handler for Python source files (.py):
    for /f "skip=2 tokens=1,2*" %%i in ('reg query HKCR\.py /ve') do set "file_type=%%k"
    for /f "skip=2 tokens=1,2*" %%i in ('reg query HKCR\%file_type%\shell\open\command /ve') do echo %%k
    

... and improved version:

SOLUTION 2b

    
    
    @echo off
    setlocal EnableDelayedExpansion
    echo Python interpreter accessible through the system PATH:
    where python
    if not errorlevel 1 (
        python -c "from __future__ import print_function; import sys; print(sys.version)"
    )
    echo ---
    echo Python interpreter registered as a handler for Python source files (.py):
    reg query HKCR\.py /ve >nul 2>&1
    if errorlevel 1 (
        echo No "HKEY_CLASSES_ROOT\.py" registry key found
    ) else (
        for /f "skip=2 tokens=1,2*" %%i in ('reg query HKCR\.py /ve 2^>nul') do set "file_type=%%k"
        if "!file_type!"=="(value not set)" (
            echo "No file type set for .py extension"
        ) else (
            reg query HKCR\!file_type!\shell\open\command /ve >nul 2>&1
            if errorlevel 1 (
                echo No "HKEY_CLASSES_ROOT\!file_type!\shell\open\command" registry key found
            ) else (
                for /f "skip=2 tokens=1,2*" %%i in ('reg query HKCR\!file_type!\shell\open\command /ve 2^>nul') do set "handler=%%k"
                if "!handler!"=="(value not set)" (
                    echo No command set for !file_type!
                ) else (
                    echo !handler!
                )
            )
        )
    )
    

