diff --git a/README b/README
new file mode 100644
index 0000000000000000000000000000000000000000..f4ef45f7edb2b80a7cd3f1edfb14b718c8c53115
--- /dev/null
+++ b/README
@@ -0,0 +1,6 @@
+Miscellaneous Python lifesavers.
+
+Andreas Kloeckner <inform@tiker.net>
+
+Includes Michele Simionato's decorator module, from
+http://www.phyast.pitt.edu/~micheles/python/
diff --git a/src/__init__.py b/src/__init__.py
index fdcc6157ce40dbcd2e9c790070b870bdd50494e7..fd2d0e886789005c35736418f13d582cf84b0187 100644
--- a/src/__init__.py
+++ b/src/__init__.py
@@ -1,4 +1,8 @@
-import math, sys, operator, types
+import math
+import sys
+import operator
+import types
+from pytools.decorator import decorator
 
 
 
@@ -24,20 +28,33 @@ class Reference(object):
 
 
 
-class FunctionValueCache(object):
-    def __init__(self, function):
-        self.Function = function
-        self.ResultMap = {}
 
-    def __call__(self, *args):
-        try:
-            return self.ResultMap[args]
-        except KeyError:
-            result = self.Function(*args)
-            self.ResultMap[args] = result
-            return result
+def getattr_(obj, name, default_thunk):
+    "Similar to .setdefault in dictionaries."
+    try:
+        return getattr(obj, name)
+    except AttributeError:
+        default = default_thunk()
+        setattr(obj, name, default)
+        return default
+
+@decorator
+def memoize(func, *args):
+    # by Michele Simionato
+    # http://www.phyast.pitt.edu/~micheles/python/
+
+    dic = getattr_(func, "memoize_dic", dict)
+
+    # memoize_dic is created at the first call
+    if args in dic:
+        return dic[args]
+    else:
+        result = func(*args)
+        dic[args] = result
+        return result
+FunctionValueCache = memoize
+
 
-    
 
 
 class DictionaryWithDefault(object):
@@ -369,6 +386,10 @@ def flatten(list):
 
 
 def sum_over(function, arguments):
+    raise RuntimeError, "Horribly inefficient routine called."
+
+    # wherever this is used, it should be replaced by sum() and a generator
+    # expression.
     result = 0
     for i in arguments:
         result += function(i)
diff --git a/src/decorator.py b/src/decorator.py
new file mode 100644
index 0000000000000000000000000000000000000000..8915cf05371dd65a67c22bb720648d4ccf1ce77f
--- /dev/null
+++ b/src/decorator.py
@@ -0,0 +1,146 @@
+## The basic trick is to generate the source code for the decorated function
+## with the right signature and to evaluate it.
+## Uncomment the statement 'print >> sys.stderr, func_src'  in _decorate
+## to understand what is going on.
+
+__all__ = ["decorator", "update_wrapper", "getinfo"]
+
+import inspect, sys
+    
+def getinfo(func):
+    """
+    Returns an info dictionary containing:
+    - name (the name of the function : str)
+    - argnames (the names of the arguments : list)
+    - defaults (the values of the default arguments : tuple)
+    - signature (the signature : str)
+    - doc (the docstring : str)
+    - module (the module name : str)
+    - dict (the function __dict__ : str)
+    
+    >>> def f(self, x=1, y=2, *args, **kw): pass
+
+    >>> info = getinfo(f)
+
+    >>> info["name"]
+    'f'
+    >>> info["argnames"]
+    ['self', 'x', 'y', 'args', 'kw']
+    
+    >>> info["defaults"]
+    (1, 2)
+
+    >>> info["signature"]
+    'self, x, y, *args, **kw'
+    """
+    assert inspect.ismethod(func) or inspect.isfunction(func)
+    regargs, varargs, varkwargs, defaults = inspect.getargspec(func)
+    argnames = list(regargs)
+    if varargs:
+        argnames.append(varargs)
+    if varkwargs:
+        argnames.append(varkwargs)
+    signature = inspect.formatargspec(regargs, varargs, varkwargs, defaults,
+                                      formatvalue=lambda value: "")[1:-1]
+    return dict(name=func.__name__, argnames=argnames, signature=signature,
+                defaults = func.func_defaults, doc=func.__doc__,
+                module=func.__module__, dict=func.__dict__,
+                globals=func.func_globals, closure=func.func_closure)
+
+def update_wrapper(wrapper, wrapped, create=False):
+    """
+    An improvement over functools.update_wrapper. By default it works the
+    same, but if the 'create' flag is set, generates a copy of the wrapper
+    with the right signature and update the copy, not the original.
+    Moreovoer, 'wrapped' can be a dictionary with keys 'name', 'doc', 'module',
+    'dict', 'defaults'.
+    """
+    if isinstance(wrapped, dict):
+        infodict = wrapped
+    else: # assume wrapped is a function
+        infodict = getinfo(wrapped)
+    assert not '_wrapper_' in infodict["argnames"], \
+           '"_wrapper_" is a reserved argument name!'
+    if create: # create a brand new wrapper with the right signature
+        src = "lambda %(signature)s: _wrapper_(%(signature)s)" % infodict
+        # import sys; print >> sys.stderr, src # for debugging purposes
+        wrapper = eval(src, dict(_wrapper_=wrapper))        
+    try:
+        wrapper.__name__ = infodict['name']
+    except: # Python version < 2.4
+        pass
+    wrapper.__doc__ = infodict['doc']
+    wrapper.__module__ = infodict['module']
+    wrapper.__dict__.update(infodict['dict'])
+    wrapper.func_defaults = infodict['defaults']
+    return wrapper
+
+# the real meat is here
+def _decorator(caller, func):
+    infodict = getinfo(func)
+    argnames = infodict['argnames']
+    assert not ('_call_' in argnames or '_func_' in argnames), \
+           'You cannot use _call_ or _func_ as argument names!'
+    src = "lambda %(signature)s: _call_(_func_, %(signature)s)" % infodict
+    dec_func = eval(src, dict(_func_=func, _call_=caller))
+    return update_wrapper(dec_func, func)
+
+def decorator(caller, func=None):
+    """
+    General purpose decorator factory: takes a caller function as
+    input and returns a decorator with the same attributes.
+    A caller function is any function like this::
+
+     def caller(func, *args, **kw):
+         # do something
+         return func(*args, **kw)
+    
+    Here is an example of usage:
+
+    >>> @decorator
+    ... def chatty(f, *args, **kw):
+    ...     print "Calling %r" % f.__name__
+    ...     return f(*args, **kw)
+
+    >>> chatty.__name__
+    'chatty'
+    
+    >>> @chatty
+    ... def f(): pass
+    ...
+    >>> f()
+    Calling 'f'
+
+    For sake of convenience, the decorator factory can also be called with
+    two arguments. In this casem ``decorator(caller, func)`` is just a
+    shortcut for ``decorator(caller)(func)``.
+    """
+    if func is None: # return a decorator function
+        return update_wrapper(lambda f : _decorator(caller, f), caller)
+    else: # return a decorated function
+        return _decorator(caller, func)
+
+if __name__ == "__main__":
+    import doctest; doctest.testmod()
+
+#######################     LEGALESE    ##################################
+      
+##   Redistributions of source code must retain the above copyright 
+##   notice, this list of conditions and the following disclaimer.
+##   Redistributions in bytecode form must reproduce the above copyright
+##   notice, this list of conditions and the following disclaimer in
+##   the documentation and/or other materials provided with the
+##   distribution. 
+
+##   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+##   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+##   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+##   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+##   HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+##   INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+##   BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+##   OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+##   ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
+##   TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+##   USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+##   DAMAGE.