ubuntu18.0 ROS运行roscore出现的问题

出现在ROS一切都安装完成之后，想拿小海龟测试一下能否成功

小海龟测试参考链接https://blog.youkuaiyun.com/ignoreyou/article/details/79488741

但是在终端运行roscore后报出这样的错误：

Traceback (most recent call last):
  File "/opt/ros/kinetic/bin/roscore", line 69, in <module>
    import roslaunch
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/__init__.py", line 51, in <module>
    from . import param_dump as roslaunch_param_dump
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/param_dump.py", line 40, in <module>
    import roslaunch.config
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/config.py", line 45, in <module>
    import rospkg.distro
  File "/usr/lib/python2.7/dist-packages/rospkg/distro.py", line 44, in <module>
    import yaml
  File "/usr/local/lib/python3.6/dist-packages/yaml/__init__.py", line 284
    class YAMLObject(metaclass=YAMLObjectMetaclass):
                              ^
SyntaxError: invalid syntax

解决方法

参考大佬解决方法https://blog.youkuaiyun.com/handsome_for_kill/article/details/81947978
链接里面也提到原因了，是因为python版本没有设置正确或者pythonpath没有添加
因此切换python版本：

update-alternatives --config python

输入不同版本对应的数字即可切换不同版本环境，0，1，2可分别尝试一下，我选的0，1不行，最后用的2