From a3a4f5c1447b10cee63d9fee518d0d6b5b881846 Mon Sep 17 00:00:00 2001
From: Troon <mark@tranchant.co.uk>
Date: Thu, 9 May 2019 15:26:52 +0100
Subject: [PATCH] Fixed #30310 -- Added support for looking up
 HttpHeaders.headers using underscores.

---
 django/http/request.py        | 4 ++++
 docs/ref/request-response.txt | 9 +++++++++
 docs/releases/3.0.txt         | 3 +++
 tests/requests/tests.py       | 1 +
 4 files changed, 17 insertions(+)

diff --git a/django/http/request.py b/django/http/request.py
index 1e1cc6c397..e62e2272b2 100644
--- a/django/http/request.py
+++ b/django/http/request.py
@@ -369,6 +369,10 @@ class HttpHeaders(CaseInsensitiveMapping):
                 headers[name] = value
         super().__init__(headers)
 
+    def __getitem__(self, key):
+        """Allow header lookup using underscores in place of hyphens."""
+        return super().__getitem__(key.replace('_', '-'))
+
     @classmethod
     def parse_header_name(cls, header):
         if header.startswith(cls.HTTP_PREFIX):
diff --git a/docs/ref/request-response.txt b/docs/ref/request-response.txt
index d6a336178e..58a7c3e7e4 100644
--- a/docs/ref/request-response.txt
+++ b/docs/ref/request-response.txt
@@ -199,6 +199,15 @@ All attributes should be considered read-only, unless stated otherwise.
         >>> request.headers.get('user-agent')
         Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6)
 
+    For use in, for example, Django templates, headers can also be looked up
+    using underscores in place of hyphens::
+
+        {{ request.headers.user_agent }}
+
+    .. versionchanged:: 3.0
+
+        Support for look ups using underscores was added.
+
 .. attribute:: HttpRequest.resolver_match
 
     An instance of :class:`~django.urls.ResolverMatch` representing the
diff --git a/docs/releases/3.0.txt b/docs/releases/3.0.txt
index 335ab2c0d5..daf1ef513b 100644
--- a/docs/releases/3.0.txt
+++ b/docs/releases/3.0.txt
@@ -217,6 +217,9 @@ Requests and Responses
 * Allowed :class:`~django.http.HttpResponse` to be initialized with
   :class:`memoryview` content.
 
+* For use in, for example, Django templates, :attr:`.HttpRequest.headers` now
+  allows look ups using underscores (e.g. ``user_agent``) in place of hyphens.
+
 Serialization
 ~~~~~~~~~~~~~
 
diff --git a/tests/requests/tests.py b/tests/requests/tests.py
index a97b98e8a2..0c68105bb4 100644
--- a/tests/requests/tests.py
+++ b/tests/requests/tests.py
@@ -896,6 +896,7 @@ class RequestHeadersTests(SimpleTestCase):
         request = WSGIRequest(self.ENVIRON)
         self.assertEqual(request.headers['User-Agent'], 'python-requests/1.2.0')
         self.assertEqual(request.headers['user-agent'], 'python-requests/1.2.0')
+        self.assertEqual(request.headers['user_agent'], 'python-requests/1.2.0')
         self.assertEqual(request.headers['Content-Type'], 'text/html')
         self.assertEqual(request.headers['Content-Length'], '100')