From a167fe684f4eefd651307d8e9e7d4a61e4a68629 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 10 Jun 2026 22:31:29 +0200
Subject: [PATCH] [3.14][3.15] gh-151253: Dump the Python path configuration on
 _PyCodec_InitRegistry() failure (#151250) (#151269) (#151283)

[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)
(cherry picked from commit b3a7758d8a6333501fd60c052a40ae5c958e3d14)
---
 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 209d37095a6c0b4..797615c915c3d59 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -1018,6 +1018,17 @@ def res2int(self, res):
         out = res.out.strip().decode("utf-8")
         return tuple(int(i) for i in out.split())
 
+    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 000000000000000..56d2f3b2633bb01
--- /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 d2e3f25157144a8..6fa68cdbda71a50 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_lock.h"          // PyMutex
 #include "pycore_pyerrors.h"      // _PyErr_FormatNote()
@@ -1504,6 +1505,8 @@ _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);