Constrain Joint in MoveIt

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Hi all!

I'm working on constraining joints in Moveit by expanding upon this tutorial. Below is a small reproduction of my code, as well as a copy of the error message I'm getting . From what I can tell I followed the moveit.msg documentation to the T. I'm running ROS melodic on Ubuntu 18.04.4 LTS.

My Code:

 #!/usr/bin/env python

from move_group_python_interface_tutorial import *

import moveit_msgs.msg

from std_msgs.msg import Float64

def main():

    try:
        # This is just initializing the tutorial object
        tutorial = MoveGroupPythonIntefaceTutorial()

        # construct a message
        joint_constraint = moveit_msgs.msg.JointConstraint()
        joint_constraint.joint_name = tutorial.move_group.get_joints()[0]
        joint_constraint.position = Float64(1.0)
        joint_constraint.tolerance_above = Float64(0.5)
        joint_constraint.tolerance_below = Float64(0.5)
        joint_constraint.weight = Float64(1.0)

        joint_constraint_list = []
        joint_constraint_list.append(joint_constraint)

        constraint_list = moveit_msgs.msg.Constraints()
        constraint_list.name = 'middle_of_travel'
        constraint_list.joint_constraints = joint_constraint_list

        tutorial.move_group.set_path_constraints(constraint_list)

    except KeyboardInterrupt:
        return

if __name__ == '__main__':
    main()

My error message:

Traceback (most recent call last):

  File "/home/mike/catkin_ws/src/macs_gazebo_simulation/inspection_cell_moveit_config/test.py", line 33, in <module>
    main()

  File "/home/mike/catkin_ws/src/macs_gazebo_simulation/inspection_cell_moveit_config/test.py", line 27, in main
    tutorial.move_group.set_path_constraints(constraint_list)

  File "/opt/ros/melodic/lib/python2.7/dist-packages/moveit_commander/move_group.py", line 403, in set_path_constraints
    self._g.set_path_constraints_from_msg(conversions.msg_to_string(value))

  File "/opt/ros/melodic/lib/python2.7/dist-packages/moveit_commander/conversions.py", line 49, in msg_to_string
    msg.serialize(buf)

  File "/opt/ros/melodic/lib/python2.7/dist-packages/moveit_msgs/msg/_Constraints.py", line 469, in serialize
    except struct.error as se: self._check_types(struct.error("%s: '%s' when writing '%s'" % (type(se), str(se), str(locals().get('_x', self)))))

  File "/opt/ros/melodic/lib/python2.7/dist-packages/genpy/message.py", line 343, in _check_types
    raise SerializationError(str(exc))
genpy.message.SerializationError: <class 'struct.error'>: 'required argument is not a float' when writing 'joint_name: "linear_stage_joint"
position: 
  data: 1.0
tolerance_above: 
  data: 0.5
tolerance_below: 
  data: 0.5
weight: 
  data: 1.0'