lib: drop Python 2 support in find-python.js

lib/find-python.js

@@ -18,16 +18,15 @@ PythonFinder.prototype = {
   log: logWithPrefix(log, 'find Python'),
   argsExecutable: ['-c', 'import sys; print(sys.executable);'],
   argsVersion: ['-c', 'import sys; print("%s.%s.%s" % sys.version_info[:3]);'],
-  semverRange: '2.7.x || >=3.5.0',
+  semverRange: '>=3.5.0',
 
   // These can be overridden for testing:
   execFile: cp.execFile,
   env: process.env,
   win: win,
   pyLauncher: 'py.exe',
   winDefaultLocations: [
-    path.join(process.env.SystemDrive || 'C:', 'Python37', 'python.exe'),
-    path.join(process.env.SystemDrive || 'C:', 'Python27', 'python.exe')
+    path.join(process.env.SystemDrive || 'C:', 'Python37', 'python.exe')
   ],
 
   // Logs a message at verbose level, but also saves it to be displayed later
@@ -96,11 +95,6 @@ PythonFinder.prototype = {
           before: () => { this.addLog('checking if "python" can be used') },
           check: this.checkCommand,
           arg: 'python'
-        },
-        {
-          before: () => { this.addLog('checking if "python2" can be used') },
-          check: this.checkCommand,
-          arg: 'python2'
         }
       ]
 
@@ -119,7 +113,7 @@ PythonFinder.prototype = {
         checks.push({
           before: () => {
             this.addLog(
-              'checking if the py launcher can be used to find Python')
+              'checking if the py launcher can be used to find Python 3')
           },
           check: this.checkPyLauncher
         })
@@ -188,10 +182,15 @@ PythonFinder.prototype = {
   // Distributions of Python on Windows by default install with the "py.exe"
   // Python launcher which is more likely to exist than the Python executable
   // being in the $PATH.
+  // Because the Python launcher supports Python 2 and Python 3, we should
+  // explicitly request a Python 3 version. This is done by supplying "-3" as
+  // the first command line argument. Since "py.exe -3" would be an invalid
+  // executable for "execFile", we have to use the launcher to figure out
+  // where the actual "python.exe" executable is located.
   checkPyLauncher: function checkPyLauncher (errorCallback) {
     this.log.verbose(
-      `- executing "${this.pyLauncher}" to get Python executable path`)
-    this.run(this.pyLauncher, this.argsExecutable, false,
+      `- executing "${this.pyLauncher}" to get Python 3 executable path`)
+    this.run(this.pyLauncher, ['-3', ...this.argsExecutable], false,
       function (err, execPath) {
       // Possible outcomes: same as checkCommand
         if (err) {

test/test-find-python.js

@@ -10,19 +10,15 @@ const PythonFinder = findPython.test.PythonFinder
 require('npmlog').level = 'warn'
 
 test('find python', function (t) {
-  t.plan(4)
+  t.plan(5)
 
   findPython.test.findPython(null, function (err, found) {
     t.strictEqual(err, null)
     var proc = execFile(found, ['-V'], function (err, stdout, stderr) {
       t.strictEqual(err, null)
-      if (/Python 2/.test(stderr)) {
-        t.strictEqual(stdout, '')
-        t.ok(/Python 2/.test(stderr))
-      } else {
-        t.ok(/Python 3/.test(stdout))
-        t.strictEqual(stderr, '')
-      }
+      t.notOk(/Python 2/.test(stderr))
+      t.ok(/Python 3/.test(stdout))
+      t.strictEqual(stderr, '')
     })
     proc.stdout.setEncoding('utf-8')
     proc.stderr.setEncoding('utf-8')
@@ -66,7 +62,7 @@ test('find python - python', function (t) {
       poison(f, 'execFile')
       t.strictEqual(program, '/path/python')
       t.ok(/sys\.version_info/.test(args[1]))
-      cb(null, '2.7.15')
+      cb(null, '3.9.1')
     }
     t.strictEqual(program,
       process.platform === 'win32' ? '"python"' : 'python')
@@ -146,13 +142,14 @@ test('find python - no python2, no python, unix', function (t) {
 })
 
 test('find python - no python, use python launcher', function (t) {
-  t.plan(3)
+  t.plan(4)
 
   var f = new TestPythonFinder(null, done)
   f.win = true
 
   f.execFile = function (program, args, opts, cb) {
     if (program === 'py.exe') {
+      t.notEqual(args.indexOf('-3'), -1)
       t.notEqual(args.indexOf('-c'), -1)
       return cb(null, 'Z:\\snake.exe')
     }
@@ -162,7 +159,7 @@ test('find python - no python, use python launcher', function (t) {
       cb(new Error('not found'))
     } else if (/sys\.version_info/.test(args[args.length - 1])) {
       if (program === 'Z:\\snake.exe') {
-        cb(null, '2.7.14')
+        cb(null, '3.9.0')
       } else {
         t.fail()
       }