Issue #22450: Use "Accept: */*" in the default headers for urllib.request

Lib/urllib/request.py

@@ -1625,7 +1625,7 @@ class URLopener:
         self.proxies = proxies
         self.key_file = x509.get('key_file')
         self.cert_file = x509.get('cert_file')
-        self.addheaders = [('User-Agent', self.version)]
+        self.addheaders = [('User-Agent', self.version), ('Accept', '*/*')]
         self.__tempfiles = []
         self.__unlink = os.unlink # See cleanup()
         self.tempcache = None

Misc/NEWS

@@ -70,6 +70,10 @@ Library
 - Issue #27445: Don't pass str(_charset) to MIMEText.set_payload().
   Patch by Claude Paroz.
 
+- Issue #22450: urllib now includes an "Accept: */*" header among the
+  default headers.  This makes the results of REST API requests more
+  consistent and predictable especially when proxy servers are involved.
+
 - lib2to3.pgen3.driver.load_grammar() now creates a stable cache file
   between runs given the same Grammar.txt input regardless of the hash
   randomization setting.