Consider using the "py.exe" launcher to find Python 3 as well, not just for Python 2

• Node Version: Applies to any versions of Node/NPM, but tested on Node 10.20.1 with npm 6.14.4
• Platform: This is about Windows, in general. Tested on Windows 10.
• Compiler: N/A; this is just about finding a Python binary. No compiler needed on the system to find a Python binary.
• Module: Nothing, just did findPython = require(./lib/find-python) in a little standalone .js script to test Python detection.

My script ("fpy.js") (to be saved to/called from the node-gyp repo's main folder, like so: "node fpy.js".)

findPython = require('./lib/find-python')

findPython(null, function (err, found) {
  if (err) {
    console.error(err)
  } else {
    python = found
    console.log('python was found: ' + python)
  }
})

Verbose output (from npm or node-gyp):

node.exe ./fpy.js
ERR! find Python
ERR! find Python Python is not set from command line or npm configuration
ERR! find Python Python is not set from environment variable PYTHON
ERR! find Python checking if "python3" can be used
ERR! find Python - "python3" is not in PATH or produced an error
ERR! find Python checking if "python" can be used
ERR! find Python - "python" is not in PATH or produced an error
ERR! find Python checking if "python2" can be used
ERR! find Python - "python2" is not in PATH or produced an error
ERR! find Python checking if Python is C:\Python37\python.exe
ERR! find Python - "C:\Python37\python.exe" could not be run
ERR! find Python checking if Python is C:\Python27\python.exe
ERR! find Python - "C:\Python27\python.exe" could not be run
ERR! find Python checking if the py launcher can be used to find Python 2
ERR! find Python - "py.exe" is not in PATH or produced an error
ERR! find Python
ERR! find Python **********************************************************
ERR! find Python You need to install the latest version of Python.
ERR! find Python Node-gyp should be able to find and use Python. If not,
ERR! find Python you can try one of the following options:
ERR! find Python - Use the switch --python="C:\Path\To\python.exe"
ERR! find Python   (accepted by both node-gyp and npm)
ERR! find Python - Set the environment variable PYTHON
ERR! find Python - Set the npm configuration variable python:
ERR! find Python   npm config set python "C:\Path\To\python.exe"
ERR! find Python For more information consult the documentation at:
ERR! find Python https://github.com/nodejs/node-gyp#installation
ERR! find Python **********************************************************
ERR! find Python
Error: Could not find any Python installation to use
    at PythonFinder.fail (C:\Users\[User]\node-gyp\lib\find-python.js:307:47)
    at PythonFinder.runChecks (C:\Users\[User]\node-gyp\lib\find-python.js:136:21)
    at PythonFinder.<anonymous> (C:\Users\[User]\node-gyp\lib\find-python.js:205:18)
    at PythonFinder.execFileCallback (C:\Users\[User]\node-gyp\lib\find-python.js:271:16)
    at ChildProcess.exithandler (child_process.js:301:5)
    at ChildProcess.emit (events.js:198:13)
    at maybeClose (internal/child_process.js:982:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:259:5)

---

Intro, Background, and the Gist of it

Hi folks, I’m wondering if the node-gyp team would be interested in using the py.exe launcher to find not only/exclusively Python 2, like it does now, but potentially Python 3 as well.

(I just installed Python 3.8 from python.org, in the default install location, and node-gyp can’t find it. py.exe can find it, though.)

Apparently, judging by the commit history, using the Python launcher strictly to find Python 2 dates back just over four years ago, to BEFORE node-gyp had any support for Python 3. From here: https://github.com/nodejs/node-gyp/pull/894 (The latest published version of node-gyp would have been v3.3.1 at the time, judging by the release history: https://github.com/nodejs/node-gyp/releases?after=v3.5.0)

Thus, I assume the justification for only finding Python 2 at that time would have been the following: “node-gyp can’t work with Python 3, so finding Python 3 would be counter-productive! We must only find Python 2…” (That’s no longer true, and I think it might be nice to find Python 3 with such a convenient helper/launcher like py.exe.)

---

About the py.exe Launcher, and the installation location of Python on Windows

The py.exe launcher is quite useful for finding Python. It claims to be able to find the version downloadable from python.org AND the Python downloadable from the Windows Store. Source: https://docs.python.org/3/using/windows.html#launcher) It comes with Python installers for Windows since Python 3.3.

The Python situation on Windows is a little odd now, because it seems it used to be saved under something like C:\Python[Maj[Min]\python.exe (for example: C:\Python37), but recent installers save to somewhere more like this: 'C:\Users\[User]\AppData\Local\Programs\Python\Python38-32' and in fact, the location can be customized during the install wizard. So it could end up anywhere, I guess.

I think the launcher might be the most reliable way to find Python on Windows these days. And in any case, it makes an excellent fallback. I only find that it is a shame that it isn’t being used to find Python 3.

Indeed, going to Python.org, downloading Python 3.8.x and installing it will result in a Python installation that node-gyp can’t find. I would like to approximate node-gyp’s Python finding algorithm (or require its find-python.js file directly), but not being able to find the default install location from python.org seems somehow not right. I didn’t want to re-implement what seems like a (small) oversight in the repo I’m working on.

I do think the Python from the Windows Store might end up on the path as python and/or python3, but I haven’t tested or confirmed this.

---

Suggested Solution / Notes on an Implementation

Sorry I’m not very good with JS, or I’d whip up an implementation for a PR. But I think you could really just drop the -2 here, and update the comment above that, and that should do it.

(If that solution would be sufficient, or you’d like to see it run it through the CI tests and such, I would be GLAD to whip that up as a PR.)

From a quick read of the documentation page, the py.exe launcher seems to prefer Python 3 over Python 2, so just dropping the -2 flag might not be appropriate for for the node-gyp 5.x branch (which, from what I can see, generally prefers Python 2 over Python 3.)

[cclauss]

There are several documented ways to get node-gyp to use the Python that you want. Perhaps it would be better to encourage npm/cli to upgrade to node-gyp v6 so we can retire v5.

[DeeDeeG]

Here’s a proof of concept implementation against the v5.x branch: https://github.com/DeeDeeG/node-gyp/commit/b2119e3896aa2a1c25df8a02b63bc770a47b7f89

I have tested it, and it works as intended, but it also does appear to break the tests.