Script calling batch file that sets environment variables

Question

I need to write a script, on Windows, that calls a batch file to set some environment variables, then carries out some actions that make use of those environment variables.

If the calling script is itself a batch file, this works fine.

There would be some advantages to being able to write the calling script in Python, but when I try that, the environment variables set by the batch file don't persist after it returns. I'm guessing that's because subprocess.check_call(..., shell=True) spawns a fresh copy of the command shell, which takes the environment variables with it when it dies at the end of the batch file.

Is there a way to get the environment variables to persist when set by a batch file called from Python, or is it better to resign oneself to the calling script being itself a batch file?

• Joran Beasley: why not just set the environmental variables right in python with os.environ? Im confused on why you need to call this other script
• rwallace: @JoranBeasley Because I didn't write the batch file; it's the one that ships with Microsoft C++ to set the environment variables for the compiler. I could reverse engineer it, of course, but then for all I know the result might be incorrect for the next version of Microsoft C++.
• Joran Beasley: oh I c ... could you not write a batch file that called those other batchfiles and then called the python script(so it got the environmental variables)? afaik there is no way to pass a childs environmental variables back to the parent
• rwallace: @JoranBeasley True; it would be cleaner to have my script be in one file, but I can split it into two files if necessary.
• Eryk Sun: Copy or reuse the code from distutils.msvc9compiler.query_vcvarsall. Notice how it adds & set to the command to output the environment variables.

Answer 1

Use Setx to set variables. New Cmd prompts will pick up straight away, other programns after a reboot. The existing one won't pick it up. Use Set for that.

Rem Add filter.bat to the path if not in there, setx fails if it's already there
setx path %~dp0;%path% 1>nul 2>nul

• Eryk Sun: rwallace didn't ask about permanently setting environment variables in the registry. It would be a nightmare to modify PATH, LIBPATH, LIB, and INCLUDE like that.
• Serenity: His question was how to make it persist. Persist means saved to disk in Windows. The rules are simple, each program gets a copy of it's parent. If python wants it's children to have a copy of it's environment with the right stuff in it, then PYTHON must set the variable. Windows Scripting Host can do this. Just set the wshenvironment("path") = "c:\dog". Note their are FOUR types of environments in WSH. Choose the right one.
• Serenity: Try for fun wmic environment get /format:htable > temp.htm & Start temp.htm
• Eryk Sun: rwallace just needs access to the environment variables set by vcvarsall.bat, for which I linked to the correct solution. Modifying PATH in the registry based on that value is completely wrong. It's not meant to be permanent. It's just temporarily configuring a build environment.