Override dict.copy in HTTPHeaders to return the correct type.

bdarnell · bdarnell · commit f41306da0fc7 · 2012-05-26T10:55:06.000-07:00
Closes tornadoweb#519.
diff --git a/tornado/httputil.py b/tornado/httputil.py
@@ -154,6 +154,10 @@ def update(self, *args, **kwargs):
         for k, v in dict(*args, **kwargs).iteritems():
             self[k] = v
 
+    def copy(self):
+        # default implementation returns dict(self), not the subclass
+        return HTTPHeaders(self)
+
     _NORMALIZED_HEADER_RE = re.compile(r'^[A-Z0-9][a-z0-9]*(-[A-Z0-9][a-z0-9]*)*$')
     _normalized_headers = {}
 
