Index: kernel/include/IMP/internal/AttributeTable.h
===================================================================
--- kernel/include/IMP/internal/AttributeTable.h	(revision 512)
+++ kernel/include/IMP/internal/AttributeTable.h	(working copy)
@@ -46,26 +46,21 @@
   typedef Key<T> Key;
   AttributeTable() {} 
   const Value get_value(Key k) const {
-    IMP_check(contains(k),
+    IMP_assert(contains(k),
               "Attribute \"" << k.get_string()
-              << "\" not found in table.",
-              IndexException((std::string("Invalid attribute \"")
-                              + k.get_string() + "\" requested").c_str()));
+              << "\" not found in table.");
     return map_[k.get_index()].second;
   }
 
   Value& get_value(Key k) {
-    IMP_check(contains(k),
+    IMP_assert(contains(k),
               "Attribute \"" << k.get_string()
-              << "\" not found in table.",
-              IndexException((std::string("Invalid attribute \"")
-                              + k.get_string() + "\" requested").c_str()));
+              << "\" not found in table.");
     return map_[k.get_index()].second;
   }
   void insert(Key k, Value v);
   bool contains(Key k) const {
-    IMP_check(k != Key(), "Can't search for default key",
-              IndexException("Bad index"));
+    IMP_assert(k != Key(), "Can't search for default key");
     return k.get_index() < map_.size()
            && map_[k.get_index()].first;
   }
@@ -109,9 +104,8 @@
 template <class T, class VT>
 inline void AttributeTable<T, VT>::insert(Key k, Value v)
 {
-  IMP_check(k != Key(),
-            "Can't insert default key",
-            IndexException("bad index"));
+  IMP_assert(k != Key(),
+            "Can't insert default key");
   if (map_.size() <= k.get_index()) {
     map_.resize(k.get_index()+1);
   }
Index: kernel/pyext/IMP.i
===================================================================
--- kernel/pyext/IMP.i	(revision 512)
+++ kernel/pyext/IMP.i	(working copy)
@@ -14,8 +14,18 @@
 
 /* Return derivatives from unary functions */
 %include "typemaps.i"
-%apply double &OUTPUT { IMP::Float& deriv };
+%apply double &OUTPUT { IMP::Float& };
 
+%pythoncode %{
+def check_particle(p, a):
+   if (not p.get_is_active()):
+      raise ValueError("Inactive Particle")
+   if (type(a)() == a):
+      raise IndexError("Cannot use default Index")
+   if (not p.has_attribute(a)):
+      raise IndexError("Particle does not have attribute")
+%}
+
 namespace IMP {
   %pythonprepend Model::add_particle %{
         args[1].thisown=0
@@ -86,6 +96,34 @@
   %pythonprepend MonteCarlo::set_local_optimizer %{
         args[1].thisown=0
   %}
+  %pythonprepend Particle::get_value %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::get_is_optimized %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::set_is_optimized %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::set_value %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::add_to_derivative %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::get_derivative %{
+        check_particle(args[0], args[1])
+  %}
+  %pythonprepend Particle::add_attribute %{
+        # special case since we don't want to check that the attribute is there
+        if (not args[0].get_is_active()):
+           raise ValueError("Inactive Particle")
+        if (type(args[1])() == args[1]):
+           raise IndexError("Cannot use default Index")
+        if (args[0].has_attribute(args[1])):
+           raise IndexError("Particle already has attribute")
+
+  %}
 }
 
 /* Don't wrap internal functions */
@@ -106,6 +144,7 @@
 %include "IMP/unary_functions/ClosedCubicSpline.h"
 %include "IMP/unary_functions/Cosine.h"
 %include "IMP/unary_functions/Linear.h"
+%include "IMP/unary_functions/WormLikeChain.h"
 %include "IMP/DerivativeAccumulator.h"
 %include "IMP/Restraint.h"
 %include "IMP/ScoreState.h"
@@ -128,6 +167,7 @@
 %include "IMP/Optimizer.h"
 %include "IMP/optimizers/SteepestDescent.h"
 %include "IMP/optimizers/ConjugateGradients.h"
+%include "IMP/optimizers/BrownianDynamics.h"
 %include "IMP/optimizers/MolecularDynamics.h"
 %include "IMP/optimizers/Mover.h"
 %include "IMP/optimizers/MoverBase.h"