Bug/ap 25397 python pref selection error

org.knime.python3.scripting.nodes/python-kernel-tester/PythonKernelTester.py

@@ -448,7 +448,6 @@ def check_required_modules(self, additional_required_modules=None):
         self.check_module("traceback")
         self.check_module("os")
         self.check_module("pickle")
-        self.check_module("imp")
         self.check_module("types")
         # Non-standard modules.
         self.check_module("numpy")

org.knime.python3.scripting.nodes/src/main/java/org/knime/python3/scripting/nodes/prefs/PythonKernelTester.java

@@ -103,7 +103,7 @@ private static String getPythonKernelTesterPath() throws IOException {
         if (url == null) {
             throw new IOException("Could not locate the python kernel tester script");
         }
-        return FileUtil.getFileFromURL(FileLocator.toFileURL(url)).getAbsolutePath();
+        return FileUtil.getFileFromURL(FileLocator.toFileURL(url)).getCanonicalPath();
     }
 
     private PythonKernelTester() {
@@ -149,22 +149,32 @@ private static synchronized PythonKernelTestResult testPythonInstallation(final
             final var process = runPythonKernelTester(pythonCommand, majorVersion, minimumVersion,
                 additionalRequiredModules, additionalOptionalModules, testLogger);
 
-            // Get error output.
+            // Read stdout and stderr concurrently to avoid a deadlock: if Python fills
+            // one pipe buffer while Java blocks draining the other, both sides hang.
             final var errorWriter = new StringWriter();
-            try (var err = process.getErrorStream()) {
-                IOUtils.copy(err, errorWriter, StandardCharsets.UTF_8);
+            final var outputWriter = new StringWriter();
+            final var stderrReader = new Thread(() -> {
+                try (var err = process.getErrorStream()) {
+                    IOUtils.copy(err, errorWriter, StandardCharsets.UTF_8);
+                } catch (final IOException e) {
+                    LOGGER.debug("Error reading stderr of Python kernel tester", e);
+                }
+            }, "PythonKernelTester-stderr");
+            stderrReader.start();
+            try (var in = process.getInputStream()) {
+                IOUtils.copy(in, outputWriter, StandardCharsets.UTF_8);
+            }
+            try {
+                stderrReader.join();
+            } catch (final InterruptedException e) {
+                Thread.currentThread().interrupt();
             }
+
             var errorOutput = errorWriter.toString();
             if (!errorOutput.isEmpty()) {
                 testLogger.append("Error during execution: " + errorOutput + "\n");
                 errorOutput = decorateErrorOutputForKnownProblems(errorOutput);
             }
-
-            // Get regular output.
-            final var outputWriter = new StringWriter();
-            try (var in = process.getInputStream()) {
-                IOUtils.copy(in, outputWriter, StandardCharsets.UTF_8);
-            }
             final String testOutput = outputWriter.toString();
             testLogger.append("Raw test output: \n" + testOutput + "\n");
 
@@ -223,7 +233,7 @@ private static Process runPythonKernelTester(final ExternalProcessProvider pytho
         }
         if (!additionalRequiredModules.isEmpty()) {
             commandArguments.add("-m"); // Flag for additional modules.
-            additionalOptionalModules.forEach(moduleSpec -> commandArguments.add(moduleSpec.toString()));
+            additionalRequiredModules.forEach(moduleSpec -> commandArguments.add(moduleSpec.toString()));
         }
         if (!additionalOptionalModules.isEmpty()) {
             commandArguments.add("-o");

org.knime.python3/src/main/java/org/knime/python3/SimplePythonCommand.java

@@ -48,6 +48,8 @@
  */
 package org.knime.python3;
 
+import java.io.File;
+import java.nio.file.Path;
 import java.util.List;
 
 import org.knime.externalprocessprovider.ExternalProcessProvider;
@@ -78,4 +80,52 @@ public SimplePythonCommand(final String... commands) {
     public SimplePythonCommand(final List<String> command) {
         super(command);
     }
+
+    /**
+     * Creates a {@link ProcessBuilder} for this command, prepending the Python executable's conda environment
+     * directories to {@code PATH}. On Windows, conda/pixi environments require several sub-directories to be on
+     * {@code PATH} for proper process startup:
+     * <ul>
+     * <li>The env root (contains the Python DLL)</li>
+     * <li>{@code Library/bin} (contains vcruntime, openssl, and other SxS-manifest DLLs)</li>
+     * <li>{@code Library/mingw-w64/bin} (contains mingw toolchain DLLs)</li>
+     * <li>{@code Library/usr/bin} (contains misc tools)</li>
+     * <li>{@code Scripts} (contains pip, etc.)</li>
+     * </ul>
+     * Without these, Python 3.12+ fails at startup with a Windows SxS assembly error because VC++ runtime DLLs
+     * cannot be located. Only directories that actually exist on disk are prepended to avoid polluting {@code PATH}
+     * for non-conda environments.
+     */
+    @Override
+    public ProcessBuilder createProcessBuilder() {
+        final var pb = super.createProcessBuilder();
+        final Path executableDir = getExecutablePath().getParent();
+        if (executableDir != null) {
+            final var env = pb.environment();
+            // ProcessBuilder.environment() on Windows stores keys case-insensitively but
+            // preserves the original casing. Find the existing key to avoid duplicates.
+            final String pathKey = env.keySet().stream() //
+                .filter(k -> k.equalsIgnoreCase("PATH")) //
+                .findFirst() //
+                .orElse("PATH");
+            final String existingPath = env.getOrDefault(pathKey, "");
+
+            // Standard conda/pixi activation paths for Windows, in activation order.
+            final var dirsToAdd = new StringBuilder();
+            for (final String subDir : new String[]{"", "Library\\bin", "Library\\mingw-w64\\bin",
+                "Library\\usr\\bin", "Scripts"}) {
+                final var candidate = subDir.isEmpty() ? executableDir : executableDir.resolve(subDir);
+                if (candidate.toFile().isDirectory()) {
+                    if (dirsToAdd.length() > 0) {
+                        dirsToAdd.append(File.pathSeparator);
+                    }
+                    dirsToAdd.append(candidate);
+                }
+            }
+            if (dirsToAdd.length() > 0) {
+                env.put(pathKey, dirsToAdd + File.pathSeparator + existingPath);
+            }
+        }
+        return pb;
+    }
 }