From 10f616cf3939f87605081d05c1913ba630046c54 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 10 Jun 2026 22:03:27 +0200
Subject: [PATCH] [3.15] gh-151253: Dump the Python path configuration on
 _PyCodec_InitRegistry() failure (#151250) (#151269)

gh-151253: Dump the Python path configuration on _PyCodec_InitRegistry() failure (#151250)

If "import encodings" fails at Python startup, dump the Python path
configuration to help users debugging their configuration. The
encodings module is the first module imported during Python startup.

(cherry picked from commit 7b6e98911e1485be13817f2aedbbfadb1c4ea876)
---
 Lib/test/test_cmd_line.py                             | 11 +++++++++++
 .../2026-06-10-15-42-46.gh-issue-151253.7MMQ8P.rst    |  3 +++
 Python/codecs.c                                       |  3 +++
 3 files changed, 17 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-06-10-15-42-46.gh-issue-151253.7MMQ8P.rst

diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
index 3b556ec3144..a8645af26b2 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -1314,6 +1314,17 @@ def test_presite(self):
         proc = assert_python_ok("-X", f"presite={entrypoint}", "-c", "pass")
         self.assertEqual(proc.out.rstrip(), b"presite func")
 
+    def test_dump_path_config(self):
+        # gh-151253: At the first import (import encodings) during Python
+        # startup, if the import fails, dump the Python path configuration.
+        nonexistent = '/nonexistent-python-path'
+        # Use -X frozen_modules=off to disable frozen encodings module
+        # on release build.
+        cmd = ["-X", "frozen_modules=off", "-c", "pass"]
+        proc = assert_python_failure(*cmd, PYTHONHOME=nonexistent)
+        self.assertIn(b'Python path configuration:', proc.err)
+        self.assertIn(f"PYTHONHOME = '{nonexistent}'".encode(), proc.err)
+
 
 @unittest.skipIf(interpreter_requires_environment(),
                  'Cannot run -I tests when PYTHON env vars are required.')
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-06-10-15-42-46.gh-issue-151253.7MMQ8P.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-10-15-42-46.gh-issue-151253.7MMQ8P.rst
new file mode 100644
index 00000000000..56d2f3b2633
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-10-15-42-46.gh-issue-151253.7MMQ8P.rst
@@ -0,0 +1,3 @@
+If ``import encodings`` (first import) fails at Python startup, dump the
+Python path configuration to help users debugging their configuration. Patch
+by Victor Stinner.
diff --git a/Python/codecs.c b/Python/codecs.c
index 0bde56c0ac6..2cf8460d208 100644
--- a/Python/codecs.c
+++ b/Python/codecs.c
@@ -10,6 +10,7 @@ Copyright (c) Corporation for National Research Initiatives.
 
 #include "Python.h"
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
+#include "pycore_initconfig.h"    // _Py_DumpPathConfig()
 #include "pycore_interp.h"        // PyInterpreterState.codec_search_path
 #include "pycore_pyerrors.h"      // _PyErr_FormatNote()
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
@@ -1685,6 +1686,8 @@ _PyCodec_InitRegistry(PyInterpreterState *interp)
     // search functions, so this is done after everything else is initialized.
     PyObject *mod = PyImport_ImportModule("encodings");
     if (mod == NULL) {
+        PyThreadState *tstate = _PyThreadState_GET();
+        _Py_DumpPathConfig(tstate);
         return PyStatus_Error("Failed to import encodings module");
     }
     Py_DECREF(mod);