From f53741a53dd23cf7d9675d00a738a784a7925e8e Mon Sep 17 00:00:00 2001
From: CHINMAY <89741289+Das-Chinmay@users.noreply.github.com>
Date: Thu, 26 Mar 2026 22:03:37 -0700
Subject: [PATCH 1/4] gh-47005: fix do_open() to let regular headers override
 unredirected headers

AbstractHTTPHandler.do_open() was building the request header dict by
starting with unredirected_hdrs and only inserting regular headers that
were not already present, giving unredirected headers priority.  This
contradicts get_header() and header_items(), both of which give regular
headers the higher priority.

Fix by unconditionally updating with req.headers so that a header set
via add_header() always overrides one set via add_unredirected_header().
---
 Lib/test/test_urllib2.py | 17 +++++++++++++++++
 Lib/urllib/request.py    |  3 +--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index 3a77b9e5ab7928..b3cbb20557e37b 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -980,6 +980,23 @@ def test_http(self):
             self.assertEqual(req.unredirected_hdrs["Host"], "baz")
             self.assertEqual(req.unredirected_hdrs["Spam"], "foo")
 
+    def test_http_header_priority(self):
+        # gh-47005: regular headers set via add_header() must override
+        # unredirected headers with the same name in do_open(), consistent
+        # with get_header() and header_items().
+        h = urllib.request.AbstractHTTPHandler()
+        h.parent = MockOpener()
+
+        req = Request("http://example.com/", headers={"Content-Type": "application/json"})
+        req.timeout = None
+        req.add_unredirected_header("Content-Type", "application/x-www-form-urlencoded")
+
+        http = MockHTTPClass()
+        h.do_open(http, req)
+
+        sent_headers = dict(http.req_headers)
+        self.assertEqual(sent_headers["Content-Type"], "application/json")
+
     def test_http_body_file(self):
         # A regular file - chunked encoding is used unless Content Length is
         # already set.
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index f5f17f223a4585..660301fef61258 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1293,8 +1293,7 @@ def do_open(self, http_class, req, **http_conn_args):
         h.set_debuglevel(self._debuglevel)
 
         headers = dict(req.unredirected_hdrs)
-        headers.update({k: v for k, v in req.headers.items()
-                        if k not in headers})
+        headers.update(req.headers)
 
         # TODO(jhylton): Should this be redesigned to handle
         # persistent connections?

From dec0f6bd5b924a0863ea556beda16124cfd1b774 Mon Sep 17 00:00:00 2001
From: CHINMAY <89741289+Das-Chinmay@users.noreply.github.com>
Date: Thu, 26 Mar 2026 23:10:27 -0700
Subject: [PATCH 2/4] gh-47005: add news entry

---
 .../Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst     | 4 ++++
 1 file changed, 4 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst

diff --git a/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst b/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst
new file mode 100644
index 00000000000000..a7c65e7d234bbc
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst
@@ -0,0 +1,4 @@
+Fix :meth:`urllib.request.AbstractHTTPHandler.do_open` to give regular
+headers set via :meth:`~urllib.request.Request.add_header` priority over
+unredirected headers, consistent with :meth:`~urllib.request.Request.get_header`
+and :meth:`~urllib.request.Request.header_items`.

From e384ce14c680d7ccacdffe5ebe758adf64810e25 Mon Sep 17 00:00:00 2001
From: CHINMAY <89741289+Das-Chinmay@users.noreply.github.com>
Date: Thu, 26 Mar 2026 23:25:33 -0700
Subject: [PATCH 3/4] gh-47005: trigger CI rerun


From 76d74472a2ab4bf0a1cd41a3539f4c0002297b25 Mon Sep 17 00:00:00 2001
From: CHINMAY <89741289+Das-Chinmay@users.noreply.github.com>
Date: Thu, 26 Mar 2026 23:29:58 -0700
Subject: [PATCH 4/4] gh-47005: fix invalid cross-reference in news entry

---
 .../next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst b/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst
index a7c65e7d234bbc..646367f0fa069d 100644
--- a/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst
+++ b/Misc/NEWS.d/next/Library/2026-03-26-00-00-00.gh-issue-47005.xxc89c.rst
@@ -1,4 +1,4 @@
-Fix :meth:`urllib.request.AbstractHTTPHandler.do_open` to give regular
+Fix :meth:`!urllib.request.AbstractHTTPHandler.do_open` to give regular
 headers set via :meth:`~urllib.request.Request.add_header` priority over
 unredirected headers, consistent with :meth:`~urllib.request.Request.get_header`
 and :meth:`~urllib.request.Request.header_items`.