I am working on a C# program that has to run some Python code for one particular task. (The Python code is complex and was developed by another team. Reproducing its functionality in C# is not an option.)

I am trying to update my program’s installer file to account for this: I want it to check if the user (who is installing my program) has Python installed and that it meets my minimum-version requirement. If not, I will prompt the user to download and install the latest version of Python.

However, I cannot figure out how to perform this check.

My own computer has both Python 3.9 and Python 3.10 installed, but when I type “python -V” in a command prompt, I can see that 3.10 is being used. When I debug my C# solution locally, all I need to do to run the Python code is use “python.exe” (I don’t need to provide the full path). I assume this is all because my %PATH% environment variable contains C:Python310. But how can my installer ask if the user’s computer knows where to find python.exe and, if it can find it, what version it is?

If the answer is to check Windows registry keys, I’m not sure what to do there…

My registry has entries for both 3.10 and 3.9 in HKEY_LOCAL_MACHINESOFTWAREPythonPythonCore, but I don’t see anything there that is indicating that 3.10 will be used by default.

I found another Stack Overflow question where someone said to use the key at HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionApp PathsPython.exe, but my registry does not have a value there at all, so this is definitely not a reliable approach.

Also, I know that I could just make my installer try to run “python.exe” the same way my code does, but run it with the “–version” argument and just check the version number that gets spit out, but I keep seeing warnings that this will only work if Python is in the user’s %PATH% environment variable, and it’s not clear to me whether installing Python would cause it to be added there by default or not.

So now I’m worried that I will need to do something very complicated, like… (pseudo-code)

try to run python.exe with --version

if a version is returned that is too low
   prompt to install
else if error or nothing returned
   if the registry path HKEY_LOCAL_MACHINESOFTWAREPythonPythonCore exists
      if version there is too low
         prompt to install
      else
         prompt to reinstall or prompt to add to PATH variable (this will be another question)
   else
      prompt to install

Is all of that really necessary? Is there a cleaner or faster way?