gh-144249: Report filename in SSLContext.load_cert_chain errors (#144250)

When user tries to load a certificate chain, attach the related
filename to the exception being raised. Improving user experience.

Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Lib/test/test_ssl.py

diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 9dc99fb..6023c89 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -131,6 +131,7 @@ def data_file(*name):
 EMPTYCERT = data_file("nullcert.pem")
 BADCERT = data_file("badcert.pem")
 NONEXISTINGCERT = data_file("XXXnonexisting.pem")
+NONEXISTINGKEY = data_file("XXXnonexistingkey.pem")
 BADKEY = data_file("badkey.pem")
 NOKIACERT = data_file("nokia.pem")
 NULLBYTECERT = data_file("nullbytecert.pem")
@@ -1229,6 +1230,11 @@ def test_load_cert_chain(self):
         with self.assertRaises(OSError) as cm:
             ctx.load_cert_chain(NONEXISTINGCERT)
         self.assertEqual(cm.exception.errno, errno.ENOENT)
+        self.assertEqual(cm.exception.filename, NONEXISTINGCERT)
+        with self.assertRaises(OSError) as cm:
+            ctx.load_cert_chain(CERTFILE, keyfile=NONEXISTINGKEY)
+        self.assertEqual(cm.exception.errno, errno.ENOENT)
+        self.assertEqual(cm.exception.filename, NONEXISTINGKEY)
         with self.assertRaisesRegex(ssl.SSLError, "PEM (lib|routines)"):
             ctx.load_cert_chain(BADCERT)
         with self.assertRaisesRegex(ssl.SSLError, "PEM (lib|routines)"):

Misc/NEWS.d/next/Library/2026-01-27-09-58-52.gh-issue-144249.mCIy95.rst

diff --git a/Misc/NEWS.d/next/Library/2026-01-27-09-58-52.gh-issue-144249.mCIy95.rst b/Misc/NEWS.d/next/Library/2026-01-27-09-58-52.gh-issue-144249.mCIy95.rst
new file mode 100644
index 0000000..52f27ce
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-27-09-58-52.gh-issue-144249.mCIy95.rst
@@ -0,0 +1,2 @@
+Add filename context to :exc:`OSError` exceptions raised by
+:func:`ssl.SSLContext.load_cert_chain`, allowing users to have more context.

Modules/_ssl.c

diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 22865bd..66d699b 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -4517,7 +4517,8 @@ load_cert_chain_lock_held(PySSLContext *self, _PySSLPasswordInfo *pw_info,
             /* the password callback has already set the error information */
         }
         else if (errno != 0) {
-            PyErr_SetFromErrno(PyExc_OSError);
+            PyErr_SetFromErrnoWithFilename(PyExc_OSError,
+                PyBytes_AS_STRING(certfile_bytes));
             ERR_clear_error();
         }
         else {
@@ -4537,7 +4538,8 @@ load_cert_chain_lock_held(PySSLContext *self, _PySSLPasswordInfo *pw_info,
             /* the password callback has already set the error information */
         }
         else if (errno != 0) {
-            PyErr_SetFromErrno(PyExc_OSError);
+            PyErr_SetFromErrnoWithFilename(PyExc_OSError,
+                PyBytes_AS_STRING(keyfile_bytes ? keyfile_bytes : certfile_bytes));
             ERR_clear_error();
         }
         else {