Index: Lib/wsgiref/headers.py
===================================================================
--- Lib/wsgiref/headers.py	(revision 86572)
+++ Lib/wsgiref/headers.py	(working copy)
@@ -24,13 +24,12 @@
     else:
         return param
 
-
 class Headers:
-
     """Manage a collection of HTTP response headers"""
 
-    def __init__(self,headers):
-        if type(headers) is not list:
+    def __init__(self, headers=None):
+        headers = headers if headers is not None else []
+        if not isinstance(headers, list):
             raise TypeError("Headers must be a list of name/value tuples")
         self._headers = headers
         if __debug__:
@@ -40,7 +39,7 @@
 
     def _convert_string_type(self, value):
         """Convert/check value type."""
-        if type(value) is str:
+        if isinstance(value, str):
             return value
         raise AssertionError("Header names/values must be"
             " of type str (got {0})".format(repr(value)))
@@ -55,7 +54,7 @@
         self._headers.append(
             (self._convert_string_type(name), self._convert_string_type(val)))
 
-    def __delitem__(self,name):
+    def __delitem__(self, name):
         """Delete all occurrences of a header, if present.
 
         Does *not* raise an exception if the header is missing.
@@ -63,7 +62,7 @@
         name = self._convert_string_type(name.lower())
         self._headers[:] = [kv for kv in self._headers if kv[0].lower() != name]
 
-    def __getitem__(self,name):
+    def __getitem__(self, name):
         """Get the first header value for 'name'
 
         Return None if the header is missing instead of raising an exception.
@@ -78,7 +77,6 @@
         """Return true if the message contains the header."""
         return self.get(name) is not None
 
-
     def get_all(self, name):
         """Return a list of all the values for the named field.
 
@@ -88,18 +86,16 @@
         If no fields exist with the given name, returns an empty list.
         """
         name = self._convert_string_type(name.lower())
-        return [kv[1] for kv in self._headers if kv[0].lower()==name]
+        return [v for k, v in self._headers if k.lower() == name]
 
-
-    def get(self,name,default=None):
+    def get(self, name, default=None):
         """Get the first header value for 'name', or return 'default'"""
         name = self._convert_string_type(name.lower())
-        for k,v in self._headers:
-            if k.lower()==name:
+        for k, v in self._headers:
+            if k.lower() == name:
                 return v
         return default
 
-
     def keys(self):
         """Return a list of all the header field names.