Fix finding Python within virtualenv on Windows (#2034)

## Changes
Simplify logic for selecting Python to run when calculating default whl
build command: "python" on Windows and "python3" everywhere.

Python installers from python.org do not install python3.exe. In
virtualenv there is no python3.exe.

## Tests
Added new unit tests to create real venv with uv and simulate activation
by prepending venv/bin to PATH.

.github/workflows/push.yml

@@ -40,6 +40,9 @@ jobs:
         with:
           python-version: '3.9'
 
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+
       - name: Set go env
         run: |
           echo "GOPATH=$(go env GOPATH)" >> $GITHUB_ENV

bundle/artifacts/whl/infer.go

@@ -16,12 +16,6 @@ type infer struct {
 func (m *infer) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics {
 	artifact := b.Config.Artifacts[m.name]
 
-	// TODO use python.DetectVEnvExecutable once bundle has a way to specify venv path
-	py, err := python.DetectExecutable(ctx)
-	if err != nil {
-		return diag.FromErr(err)
-	}
-
 	// Note: using --build-number (build tag) flag does not help with re-installing
 	// libraries on all-purpose clusters. The reason is that `pip` ignoring build tag
 	// when upgrading the library and only look at wheel version.
@@ -36,7 +30,9 @@ func (m *infer) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics {
 	//   version=datetime.datetime.utcnow().strftime("%Y%m%d.%H%M%S"),
 	// ...
 	//)
-	artifact.BuildCommand = fmt.Sprintf(`"%s" setup.py bdist_wheel`, py)
+
+	py := python.GetExecutable()
+	artifact.BuildCommand = fmt.Sprintf(`%s setup.py bdist_wheel`, py)
 
 	return nil
 }

bundle/config/mutator/python/python_mutator_test.go

@@ -541,7 +541,7 @@ func TestLoadDiagnosticsFile_nonExistent(t *testing.T) {
 
 func TestInterpreterPath(t *testing.T) {
 	if runtime.GOOS == "windows" {
-		assert.Equal(t, "venv\\Scripts\\python3.exe", interpreterPath("venv"))
+		assert.Equal(t, "venv\\Scripts\\python.exe", interpreterPath("venv"))
 	} else {
 		assert.Equal(t, "venv/bin/python3", interpreterPath("venv"))
 	}
@@ -673,7 +673,7 @@ func withFakeVEnv(t *testing.T, venvPath string) {
 
 func interpreterPath(venvPath string) string {
 	if runtime.GOOS == "windows" {
-		return filepath.Join(venvPath, "Scripts", "python3.exe")
+		return filepath.Join(venvPath, "Scripts", "python.exe")
 	} else {
 		return filepath.Join(venvPath, "bin", "python3")
 	}

libs/python/detect.go

@@ -11,6 +11,19 @@ import (
 	"runtime"
 )
 
+// GetExecutable gets appropriate python binary name for the platform
+func GetExecutable() string {
+	// On Windows when virtualenv is created, the <env>/Scripts directory
+	// contains python.exe but no python3.exe.
+	// Most installers (e.g. the ones from python.org) only install python.exe and not python3.exe
+
+	if runtime.GOOS == "windows" {
+		return "python"
+	} else {
+		return "python3"
+	}
+}
+
 // DetectExecutable looks up the path to the python3 executable from the PATH
 // environment variable.
 //
@@ -25,7 +38,9 @@ func DetectExecutable(ctx context.Context) (string, error) {
 	// the parent directory tree.
 	//
 	// See https://github.com/pyenv/pyenv#understanding-python-version-selection
-	out, err := exec.LookPath("python3")
+
+	out, err := exec.LookPath(GetExecutable())
+
 	// most of the OS'es have python3 in $PATH, but for those which don't,
 	// we perform the latest version lookup
 	if err != nil && !errors.Is(err, exec.ErrNotFound) {
@@ -54,7 +69,7 @@ func DetectExecutable(ctx context.Context) (string, error) {
 func DetectVEnvExecutable(venvPath string) (string, error) {
 	interpreterPath := filepath.Join(venvPath, "bin", "python3")
 	if runtime.GOOS == "windows" {
-		interpreterPath = filepath.Join(venvPath, "Scripts", "python3.exe")
+		interpreterPath = filepath.Join(venvPath, "Scripts", "python.exe")
 	}
 
 	if _, err := os.Stat(interpreterPath); err != nil {

libs/python/detect_test.go

@@ -39,7 +39,7 @@ func TestDetectVEnvExecutable_badLayout(t *testing.T) {
 
 func interpreterPath(venvPath string) string {
 	if runtime.GOOS == "windows" {
-		return filepath.Join(venvPath, "Scripts", "python3.exe")
+		return filepath.Join(venvPath, "Scripts", "python.exe")
 	} else {
 		return filepath.Join(venvPath, "bin", "python3")
 	}

libs/python/pythontest/pythontest.go

@@ -0,0 +1,107 @@
+package pythontest
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/databricks/cli/internal/testutil"
+	"github.com/stretchr/testify/require"
+)
+
+type VenvOpts struct {
+	// input
+	PythonVersion    string
+	skipVersionCheck bool
+
+	// input/output
+	Dir  string
+	Name string
+
+	// output:
+	// Absolute path to venv
+	EnvPath string
+
+	// Absolute path to venv/bin or venv/Scripts, depending on OS
+	BinPath string
+
+	// Absolute path to python binary
+	PythonExe string
+}
+
+func CreatePythonEnv(opts *VenvOpts) error {
+	if opts == nil || opts.PythonVersion == "" {
+		return errors.New("PythonVersion must be provided")
+	}
+	if opts.Name == "" {
+		opts.Name = testutil.RandomName("test-venv-")
+	}
+
+	cmd := exec.Command("uv", "venv", opts.Name, "--python", opts.PythonVersion, "--seed", "-q")
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Dir = opts.Dir
+	err := cmd.Run()
+	if err != nil {
+		return err
+	}
+
+	opts.EnvPath, err = filepath.Abs(filepath.Join(opts.Dir, opts.Name))
+	if err != nil {
+		return err
+	}
+
+	_, err = os.Stat(opts.EnvPath)
+	if err != nil {
+		return fmt.Errorf("cannot stat EnvPath %s: %s", opts.EnvPath, err)
+	}
+
+	if runtime.GOOS == "windows" {
+		// https://github.com/pypa/virtualenv/commit/993ba1316a83b760370f5a3872b3f5ef4dd904c1
+		opts.BinPath = filepath.Join(opts.EnvPath, "Scripts")
+		opts.PythonExe = filepath.Join(opts.BinPath, "python.exe")
+	} else {
+		opts.BinPath = filepath.Join(opts.EnvPath, "bin")
+		opts.PythonExe = filepath.Join(opts.BinPath, "python3")
+	}
+
+	_, err = os.Stat(opts.BinPath)
+	if err != nil {
+		return fmt.Errorf("cannot stat BinPath %s: %s", opts.BinPath, err)
+	}
+
+	_, err = os.Stat(opts.PythonExe)
+	if err != nil {
+		return fmt.Errorf("cannot stat PythonExe %s: %s", opts.PythonExe, err)
+	}
+
+	if !opts.skipVersionCheck {
+		cmd := exec.Command(opts.PythonExe, "--version")
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			return fmt.Errorf("Failed to run %s --version: %s", opts.PythonExe, err)
+		}
+		outString := string(out)
+		expectVersion := "Python " + opts.PythonVersion
+		if !strings.HasPrefix(outString, expectVersion) {
+			return fmt.Errorf("Unexpected output from %s --version: %v (expected %v)", opts.PythonExe, outString, expectVersion)
+		}
+	}
+
+	return nil
+}
+
+func RequireActivatedPythonEnv(t *testing.T, ctx context.Context, opts *VenvOpts) {
+	err := CreatePythonEnv(opts)
+	require.NoError(t, err)
+	require.DirExists(t, opts.BinPath)
+
+	newPath := fmt.Sprintf("%s%c%s", opts.BinPath, os.PathListSeparator, os.Getenv("PATH"))
+	t.Setenv("PATH", newPath)
+}

libs/python/pythontest/pythontest_test.go

@@ -0,0 +1,43 @@
+package pythontest
+
+import (
+	"context"
+	"os/exec"
+	"path/filepath"
+	"testing"
+
+	"github.com/databricks/cli/libs/python"
+	"github.com/stretchr/testify/require"
+)
+
+func TestVenvSuccess(t *testing.T) {
+	// Test at least two version to ensure we capture a case where venv version does not match system one
+	for _, pythonVersion := range []string{"3.11", "3.12"} {
+		t.Run(pythonVersion, func(t *testing.T) {
+			ctx := context.Background()
+			dir := t.TempDir()
+			opts := VenvOpts{
+				PythonVersion: pythonVersion,
+				Dir:           dir,
+			}
+			RequireActivatedPythonEnv(t, ctx, &opts)
+			require.DirExists(t, opts.EnvPath)
+			require.DirExists(t, opts.BinPath)
+			require.FileExists(t, opts.PythonExe)
+
+			pythonExe, err := exec.LookPath(python.GetExecutable())
+			require.NoError(t, err)
+			require.Equal(t, filepath.Dir(pythonExe), filepath.Dir(opts.PythonExe))
+			require.FileExists(t, pythonExe)
+		})
+	}
+}
+
+func TestWrongVersion(t *testing.T) {
+	require.Error(t, CreatePythonEnv(&VenvOpts{PythonVersion: "4.0"}))
+}
+
+func TestMissingVersion(t *testing.T) {
+	require.Error(t, CreatePythonEnv(nil))
+	require.Error(t, CreatePythonEnv(&VenvOpts{}))
+}