wstool failed to initiate

edit

I'm following this instruction trying to install ROS on my mac http://wiki.ros.org/kinetic/Installat... and I've got environment variables both set for python2.7 and python 3.9 by calling:

$ mkdir -p ~/Library/Python/2.7/lib/python/site-packages
$ echo "$(brew --prefix)/lib/python2.7/site-packages" >> ~/Library/Python/2.7/lib/python/site-packages/homebrew.pth
$ mkdir -p ~/Library/Python/3.9/lib/python/site-packages
$ echo "$(brew --prefix)/lib/python3.9/site-packages" >> ~/Library/Python/3.9/lib/python/site-packages/homebrew.pth

I have successfully generated the install file by calling: rosinstall_generator desktop --rosdistro kinetic --deps --wet-only --tar > kinetic-desktop-wet.rosinstall but when I try to init the install file using wstool it is giving me the following errors:

Using initial elements from: kinetic-desktop-wet.rosinstall
/usr/local/lib/python3.9/site-packages/wstool/config_yaml.py:74: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
  yamldata = yaml.load(stream)
Writing /Users/nelldu/ros_catkin_ws/src/.rosinstall
Traceback (most recent call last):
  File "/usr/local/bin/wstool", line 62, in <module>
    sys.exit(wstool.wstool_cli.wstool_main(sys.argv))
  File "/usr/local/lib/python3.9/site-packages/wstool/wstool_cli.py", line 174, in wstool_main
    return commands[command](args)
  File "/usr/local/lib/python3.9/site-packages/wstool/multiproject_cli.py", line 475, in cmd_init
    install_success = multiproject_cmd.cmd_install_or_update(
  File "/usr/local/lib/python3.9/site-packages/wstool/multiproject_cmd.py", line 414, in cmd_install_or_update
    work.run()
  File "/usr/local/lib/python3.9/site-packages/wstool/common.py", line 352, in run
    self.threads[i].start()
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/context.py", line 284, in _Popen
    return Popen(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)
  File "/usr/local/Cellar/python@3.9/3.9.7_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'cmd_install_or_update.<locals>.Installer'

Would like to know is this a yaml issue that I have to update my yaml ... (more)