From 215d2afe39978797c5a389b7de8f33860ed69400 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)
(cherry picked from commit 10f616cf3939f87605081d05c1913ba630046c54)
---
 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 f2a4514c005a4f..2f4fee0443cff3 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -1262,6 +1262,17 @@ def test_invalid_thread_local_bytecode(self):
         rc, out, err = assert_python_failure(PYTHON_TLBC="2")
         self.assertIn(b"PYTHON_TLBC=N: N is missing or invalid", err)
 
+    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 00000000000000..56d2f3b2633bb0
--- /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 4e9aecfe75c2c9..3ca0ff1fc502f7 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()
@@ -1691,6 +1692,8 @@ _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);