Improvements to collections.deque():

* Add doctests for the examples in the library reference.
* Add two methods, left() and right(), modeled after deques in C++ STL.
* Apply the new method to asynchat.py.
* Add comparison operators to make deques more substitutable for lists.
* Replace the LookupErrors with IndexErrors to more closely match lists.

Lib/asynchat.py

@@ -262,11 +262,7 @@ class fifo:
         return self.list == []
 
     def first (self):
-        it = iter(self.list)
-        try:
-            return it.next()
-        except StopIteration:
-            raise IndexError
+        return self.list.left()
 
     def push (self, data):
         self.list.append(data)