Ros-Noetic: Python 3 - PyKDL Error

edit

Hello I am trying to read a urdf file but I get error as

python3: /build/orocos-kdl-mPkyII/orocos-kdl-1.4.0/python_orocos_kdl/PyKDL/std_string.sip:52: int convertTo_std_string(PyObject*, void**, int*, PyObject*): Assertion `PyUnicode_Check(s)' failed.

I am using the recommended Ubuntu 20.04 (Focal Fossa) with ROS Noetic

It never used to happen on melodic with python2.7. I am not sure whether its a problem with the package urdf_parser_py or is it with PyKDL?.

I get the error when i try to execute,

from __future__ import print_function
import PyKDL as kdl
import urdf_parser_py.urdf as urdf

     with open(filename) as urdfFile:
                return treeFromUrdfModel(urdf.URDF.from_xml_string(urdfFile.read()))

I think my problem is similar to this, https://github.com/orocos/orocos_kine...

and I think this is the solution, https://github.com/orocos/orocos_kine...

But I am not sure how should I edit and incorporate the changes mentioned above.

My urdf file is,

<?xml version="1.0"?>
<!-- =================================================================================== -->
<!-- |    This document was autogenerated by xacro from ur5_joint_limited_robot.urdf.xacro | -->
<!-- |    EDITING THIS FILE BY HAND IS NOT RECOMMENDED                                 | -->
<!-- =================================================================================== -->
<robot name="ur5">
  <gazebo>
    <plugin filename="libgazebo_ros_control.so" name="ros_control">
      <!-- <robotNamespace>/</robotNamespace> -->
      <robotSimType>gazebo_ros_control/DefaultRobotHWSim</robotSimType>
      <legacyModeNS>true</legacyModeNS>
    </plugin>
    <!--
    <plugin name="gazebo_ros_power_monitor_controller" filename="libgazebo_ros_power_monitor.so">
      <alwaysOn>true</alwaysOn>
      <updateRate>1.0</updateRate>
      <timeout>5</timeout>
      <powerStateTopic>power_state</powerStateTopic>
      <powerStateRate>10.0</powerStateRate>
      <fullChargeCapacity>87.78</fullChargeCapacity>     
      <dischargeRate>-474</dischargeRate>
      <chargeRate>525</chargeRate>
      <dischargeVoltage>15.52</dischargeVoltage>
      <chargeVoltage>16.41</chargeVoltage>
    </plugin>
-->
  </gazebo>
  <!-- camera_link -->
  <gazebo reference="camera_link">
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
    <material>Gazebo/Green</material>
  </gazebo>
  <!-- camera -->
  <gazebo reference="camera_link">
    <sensor name="camera1" type="camera">
      <update_rate>30.0</update_rate>
      <camera name="head">
        <horizontal_fov>1.3962634</horizontal_fov>
        <image>
          <width>800</width>
          <height>800</height>
          <format>R8G8B8</format>
        </image>
        <clip>
          <near>0.02</near>
          <far>300</far>
        </clip>
        <noise>
          <type>gaussian</type>
          <!-- Noise is sampled independently per pixel on each frame.
               That pixel's noise value is added to each of its color
               channels, which at that point lie in the range [0,1]. -->
          <mean>0.0</mean>
          <stddev>0.007</stddev>
        </noise>
      </camera>
      <plugin filename="libgazebo_ros_camera.so" name="camera_controller">
        <alwaysOn>true</alwaysOn>
        <updateRate>0.0</updateRate>
        <cameraName>ur5/usbcam</cameraName>
        <imageTopicName>image_raw</imageTopicName>
        <cameraInfoTopicName>camera_info</cameraInfoTopicName>
        <frameName>camera_link_optical</frameName>
        <!-- setting hackBaseline to anything but 0.0 will cause a misalignment
            between the gazebo sensor image and the frame it is supposed to
            be attached to -->
        <hackBaseline>0.0</hackBaseline>
        <distortionK1>0.0</distortionK1>
        <distortionK2>0.0</distortionK2>
        <distortionK3>0.0</distortionK3>
        <distortionT1>0.0</distortionT1>
        <distortionT2>0.0</distortionT2>
        <CxPrime>0</CxPrime>
        <Cx>0.0</Cx>
        <Cy>0.0</Cy>
        <focalLength>0.0</focalLength>
      </plugin>
    </sensor>
  </gazebo>
  <!-- measured from model -->
  <!--property name="shoulder_height" value="0.089159" /-->
  <!--property name="shoulder_offset" value="0.13585" /-->
  <!-- shoulder_offset - elbow_offset + wrist_1_length = 0.10915 -->
  <!--property name="upper_arm_length" value="0.42500" /-->
  <!--property name="elbow_offset" value="0.1197" /-->
  <!-- CAD measured -->
  <!--property name="forearm_length" value="0.39225" /-->
  <!--property name="wrist_1_length" value="0.093 ...