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 outside of the scope of this question.

Answer 1

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?
• How to escape variables with parentheses inside if-clause in a batch file?
• Why is delayed expansion in a batch file not working in this case?
• How to split double quoted strings with embedded spaces deliminated with spaces in a batch file?

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!
            )
        )
    )
)