一键安装ros后，roscore报错

fuzz

我之前装过一次ros，但由于一些自己的失误（好像是和python有关的代码）导致roscore报错了，然后我把ros卸载了重新一键安装，但依旧报错，请教各位大神帮我看看应该如何解决。附上报错代码
roscore
Traceback (most recent call last):
File "/opt/ros/melodic/bin/roscore", line 37, in <module>
from roslaunch.nodeprocess import DEFAULT_TIMEOUT_SIGINT, DEFAULT_TIMEOUT_SIGTERM
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/init.py", line 52, in <module>
from . import param_dump as roslaunch_param_dump
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/param_dump.py", line 40, in <module>
import roslaunch.config
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/config.py", line 45, in <module>
import rospkg.distro
File "/home/fzz/.local/lib/python2.7/site-packages/rospkg/distro.py", line 44, in <module>
import yaml
File "/usr/lib/python3/dist-packages/yaml/init.py", line 284
class YAMLObject(metaclass=YAMLObjectMetaclass):
^
SyntaxError: invalid syntax
Error in sys.excepthook:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 63, in apport_excepthook
from apport.fileutils import likely_packaged, get_recent_crashes
File "/usr/lib/python3/dist-packages/apport/init.py", line 5, in <module>
from apport.report import Report
File "/usr/lib/python3/dist-packages/apport/report.py", line 30, in <module>
import apport.fileutils
File "/usr/lib/python3/dist-packages/apport/fileutils.py", line 23, in <module>
from apport.packaging_impl import impl as packaging
File "/usr/lib/python3/dist-packages/apport/packaging_impl.py", line 24, in <module>
import apt
File "/usr/lib/python3/dist-packages/apt/init.py", line 23, in <module>
import apt_pkg
ImportError: No module named apt_pkg

Original exception was:
Traceback (most recent call last):
File "/opt/ros/melodic/bin/roscore", line 37, in <module>
from roslaunch.nodeprocess import DEFAULT_TIMEOUT_SIGINT, DEFAULT_TIMEOUT_SIGTERM
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/init.py", line 52, in <module>
from . import param_dump as roslaunch_param_dump
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/param_dump.py", line 40, in <module>
import roslaunch.config
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/config.py", line 45, in <module>
import rospkg.distro
File "/home/fzz/.local/lib/python2.7/site-packages/rospkg/distro.py", line 44, in <module>
import yaml
File "/usr/lib/python3/dist-packages/yaml/init.py", line 284
class YAMLObject(metaclass=YAMLObjectMetaclass):
^
SyntaxError: invalid syntax

小鱼

@fuzz 多少的系统呀？默认的python版本是3吗

fuzz

@小鱼您好，我是u18.04，ros melodic，之前貌似是默认2，然后我根据网上教学一通瞎操作想搞成3，但是可能没有成功，所以之后roscore一直报错，我卸载后按照您的一键安装后依旧这样报错。

小鱼

@fuzz 主要原因是默认的python版本造成的，需要改回python3

fuzz

@小鱼您好，可以向您请教一下要如何操作吗，我现在刚开始接触ros还不太懂，谢谢！

小鱼

@fuzz 看你怎么改的默认的了，一般是改软链接，你要根据你改过去的方式反向操作下。

fuzz

@小鱼您好，谢谢您的意见，我按您说的尝试一下，感谢！

小鱼

@fuzz 好嘞，代码块可以用markdown包裹一下，安装相关问题在一键安装模块下提问即可。

fuzz

@小鱼您好，我按照以下方法成功修改了默认python版本
Linux Python 版本切换方法
切换python版本

update-alternatives --display python
如果出现以下错误：
update-alternatives: 错误: 无 python 的候选项，那么按下面的流程操作。

#查看多个python版本

#ls /usr/bin/python
python2.7 python3.6
#添加Python2可选项，优先级为2

sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 2
#添加Python3可选项，优先级为1

sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.6 1
#配置

sudo update-alternatives --config python
#yongyu 删除配置

sudo update-alternatives --remove python /usr/bin/python2.7

来源：https://www.csdn.net/tags/NtzaAgysNDA5NjQtYmxvZwO0O0OO0O0O.html
感谢您的指导，谢谢！

小鱼

@fuzz 客气，修改完再试试是否可以正常使用ROS

fuzz

@小鱼已经可以成功运行小乌龟了

小鱼

@fuzz

gaoxu515

@小鱼 @fuzz 按照帖子的内容修改了,又出现了下面的错误,请问大佬们怎么解决啊?谢谢~ (我的环境和fuzz的一样)

Traceback (most recent call last):
File "/opt/ros/melodic/bin/roscore", line 37, in <module>
from roslaunch.nodeprocess import DEFAULT_TIMEOUT_SIGINT, DEFAULT_TIMEOUT_SIGTERM
File "/opt/ros/melodic/lib/python2.7/dist-packages/roslaunch/init.py", line 39, in <module>
import rospkg
ModuleNotFoundError: No module named 'rospkg'

gaoxu515

解决了
pip3 install rospkg

O🐯

我装的python3可是也出现了这个问题

O🐯

@gaoxu515 为什么这个我输入后报错

O🐯

Traceback (most recent call last):
File "/usr/bin/roscore", line 37, in <module>
from roslaunch.nodeprocess import DEFAULT_TIMEOUT_SIGINT, DEFAULT_TIMEOUT_SIGTERM
File "/usr/lib/python3/dist-packages/roslaunch/init.py", line 62, in <module>
from .scriptapi import ROSLaunch
File "/usr/lib/python3/dist-packages/roslaunch/scriptapi.py", line 42, in <module>
import roslaunch.parent
File "/usr/lib/python3/dist-packages/roslaunch/parent.py", line 54, in <module>
import roslaunch.server
File "/usr/lib/python3/dist-packages/roslaunch/server.py", line 80, in <module>
from rosgraph_msgs.msg import Log
ImportError: cannot import name 'Log' from 'rosgraph_msgs.msg' (/opt/ros/rolling/lib/python3.10/site-packages/rosgraph_msgs/msg/init.py)

O🐯

@1412846703 ros2不需要输入rosroce来跑小乌龟，直接输入ros2 run turtlesim turtlesim_node
之后再开个命令行输入ros2 run turtlesim turtle_teleop_key就可以了。
详见 https://zhuanlan.zhihu.com/p/481084074#:~:text=启动小乌龟仿真器： ros2 run turtlesim turtlesim_node 启动后可以看到一个仿真器：,另外需要打开一个终端，在里面运行键盘控制的节点，命令如下： ros2 run turtlesim turtle_teleop_key 正如打印信息所述，可以通过键盘上的方向箭头移动小乌龟，可以通过G|B|V|C|D|E|R|T这些按键进行旋转到一个绝对的方向，F取消旋转，Q退出。

wesafe

@1412846703 解决了吗，我也是这个问题