diff --git a/gtsam/navigation/NavState.h b/gtsam/navigation/NavState.h
index 439e8fceb..4c8b50776 100644
--- a/gtsam/navigation/NavState.h
+++ b/gtsam/navigation/NavState.h
@@ -1,6 +1,6 @@
 /* ----------------------------------------------------------------------------
 
- * GTSAM Copyright 2010, Georgia Tech Research Corporation, 
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
  * Atlanta, Georgia 30332-0415
  * All Rights Reserved
  * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
@@ -75,18 +75,9 @@ public:
   /// @name Component Access
   /// @{
 
-  inline const Rot3& attitude() const {
-    return R_;
-  }
-  inline const Point3& position() const {
-    return t_;
-  }
-  inline const Velocity3& velocity() const {
-    return v_;
-  }
-  const Rot3& attitude(OptionalJacobian<3, 9> H) const;
-  const Point3& position(OptionalJacobian<3, 9> H) const;
-  const Velocity3& velocity(OptionalJacobian<3, 9> H) const;
+  const Rot3& attitude(OptionalJacobian<3, 9> H = boost::none) const;
+  const Point3& position(OptionalJacobian<3, 9> H = boost::none) const;
+  const Velocity3& velocity(OptionalJacobian<3, 9> H = boost::none) const;
 
   const Pose3 pose() const {
     return Pose3(attitude(), position());
diff --git a/python/handwritten/navigation/ImuFactor.cpp b/python/handwritten/navigation/ImuFactor.cpp
index e8d1e9aaa..c947ae9ee 100644
--- a/python/handwritten/navigation/ImuFactor.cpp
+++ b/python/handwritten/navigation/ImuFactor.cpp
@@ -24,18 +24,29 @@
 using namespace boost::python;
 using namespace gtsam;
 
-typedef gtsam::OptionalJacobian<9, 9> OptionalJacobian9;
+typedef gtsam::OptionalJacobian<3, 9> OptionalJacobian39;
 typedef gtsam::OptionalJacobian<9, 6> OptionalJacobian96;
+typedef gtsam::OptionalJacobian<9, 9> OptionalJacobian9;
+
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(print_overloads, print, 0, 1)
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(attitude_overloads, attitude, 0, 1)
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(position_overloads, position, 0, 1)
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(velocity_overloads, velocity, 0, 1)
 
 void exportImuFactor() {
-  class_<OptionalJacobian9>("OptionalJacobian9", init<>());
+  class_<OptionalJacobian39>("OptionalJacobian39", init<>());
   class_<OptionalJacobian96>("OptionalJacobian96", init<>());
+  class_<OptionalJacobian9>("OptionalJacobian9", init<>());
 
   class_<NavState>("NavState", init<>())
       // TODO(frank): overload with jacobians
-      //      .def("attitude", &NavState::attitude)
-      //      .def("position", &NavState::position)
-      //      .def("velocity", &NavState::velocity)
+      .def("print", &NavState::print, print_overloads())
+      .def("attitude", &NavState::attitude,
+           attitude_overloads()[return_value_policy<copy_const_reference>()])
+      .def("position", &NavState::position,
+           position_overloads()[return_value_policy<copy_const_reference>()])
+      .def("velocity", &NavState::velocity,
+           velocity_overloads()[return_value_policy<copy_const_reference>()])
       .def(repr(self))
       .def("pose", &NavState::pose);
 
@@ -77,6 +88,7 @@ void exportImuFactor() {
   // NOTE(frank): Abstract classes need boost::noncopyable
   class_<ImuFactor, bases<NonlinearFactor>, boost::shared_ptr<ImuFactor>>(
       "ImuFactor")
+      .def("error", &ImuFactor::error)
       .def(init<Key, Key, Key, Key, Key, const PreintegratedImuMeasurements&>())
       .def(repr(self));
 }
diff --git a/python/handwritten/nonlinear/NonlinearFactorGraph.cpp b/python/handwritten/nonlinear/NonlinearFactorGraph.cpp
index f1e14deda..4ba4ba008 100644
--- a/python/handwritten/nonlinear/NonlinearFactorGraph.cpp
+++ b/python/handwritten/nonlinear/NonlinearFactorGraph.cpp
@@ -1,6 +1,6 @@
 /* ----------------------------------------------------------------------------
 
- * GTSAM Copyright 2010, Georgia Tech Research Corporation, 
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation,
  * Atlanta, Georgia 30332-0415
  * All Rights Reserved
  * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
@@ -11,7 +11,7 @@
 
 /**
  * @brief exports NonlinearFactorGraph class to python
- * @author Andrew Melim 
+ * @author Andrew Melim
  * @author Ellon Paiva Mendes (LAAS-CNRS)
  **/
 
@@ -28,6 +28,13 @@ using namespace gtsam;
 
 BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(print_overloads, NonlinearFactorGraph::print, 0, 1);
 
+boost::shared_ptr<NonlinearFactor> getNonlinearFactor(
+    const NonlinearFactorGraph& graph, size_t idx) {
+  auto p = boost::dynamic_pointer_cast<NonlinearFactor>(graph.at(idx));
+  if (!p) throw std::runtime_error("No NonlinearFactor at requested index");
+  return p;
+};
+
 void exportNonlinearFactorGraph(){
 
   typedef NonlinearFactorGraph::sharedFactor sharedFactor;
@@ -36,7 +43,7 @@ void exportNonlinearFactorGraph(){
   void (NonlinearFactorGraph::*add1)(const sharedFactor&) = &NonlinearFactorGraph::add;
 
   class_<NonlinearFactorGraph>("NonlinearFactorGraph", init<>())
-    .def("size",&NonlinearFactorGraph::size)  
+    .def("size",&NonlinearFactorGraph::size)
     .def("push_back", push_back1)
     .def("add", add1)
     .def("resize", &NonlinearFactorGraph::resize)
@@ -44,4 +51,6 @@ void exportNonlinearFactorGraph(){
     .def("print", &NonlinearFactorGraph::print, print_overloads(args("s")))
   ;
 
+  def("getNonlinearFactor", getNonlinearFactor);
+
 }