diff -r 39ddcc5c7fb9 Modules/_pickle.c
--- a/Modules/_pickle.c	Sat Feb 25 19:26:39 2012 +0200
+++ b/Modules/_pickle.c	Sat Feb 25 21:51:58 2012 +0100
@@ -1,3 +1,61 @@
+/* _pickle.c - C implementation of pickle.py
+
+This module implements the following functions:
+ - dump, dumps, load, loads
+
+This module implements the following classes:
+Exceptions:
+ - PickleError
+ - PicklingError(PickleError)
+ - UnpicklingError(PickleError)
+
+Pickle protocol:
+ - PicklerObject (_pickle.Pickler)
+ - UnpicklerObject (_pickle.Unpickler)
+
+Memoization:
+ - PicklerMemoProxyObject (_pickle.PicklerMemoProxy, not directly exposed)
+ - UnpicklerMemoProxyObject (_pickle.UnpicklerMemoProxy, not directly exposed)
+
+Stack:
+ - Pdata (_pickle.Pdata, not directly exposed)
+
+The following internal structs are used:
+ - PyMemoTable and PyMemoItem, implementing a fast analog to the dict used
+   for Pickler.memo.
+
+The overall structure is as follows, with approximate line numbers (rounded to
+nearest 50, as of february 2012):
+  50 - Protocol definition
+ 150 - Forward declarations
+ 200 - Pdata implementation
+ 450 - PyMemoTable implementation
+ 700 - PicklerObject 'fast api' implementation
+ 900 - UnpicklerObject 'fast api' implementation
+1250 - PyMemoTable implementation (continued)
+1350 - PicklerObject implementation 
+3550 - PicklerMemoProxyObject implementation
+3700 - PicklerObject implementation (continued)
+3850 - UnpicklerObject implementation
+5700 - UnpicklerMemoProxyObject implementation
+5850 - UnpicklerObject implementation (continued)
+6050 - _pickle module implementation
+6500 EOF
+
+Both the PicklerObject and [UnpicklerObject] implementation follow the same
+structure: 
+ - a 'fast api' (functions starting with _Pickler [_Unpickler])
+ - a number of saving [loading] functions save_* [load_*], corresponding to
+   object types [pickle opcodes], with helper functions declared just before
+   the functions where they are needed (e.g. raw_unicode_escape)
+ - a dispatcher for these functions (save [load])
+ - the PicklerMemoProxyObject [UnpicklerMemoProxyObject] implementation
+ - functions for working with the PicklerMemoProxyObject [UnpicklerMemoPro...]
+ - functions for saving [loading] persistent IDs
+ - the object type/members/etc declaration
+
+*/
+
 #include "Python.h"
 #include "structmember.h"