Failed to load entry point 'launch': No module named 'launch.launch_description_sources'

风

各位好，我初学ROS2,现在碰到了一个问题，向大家请教一下：

按照ros2官网的创建launch文件教程，在终端输入：

cd ~ws/src
mkdir launch
touch simple.launch.py

编辑好launch文件：

from launch import LaunchDescription
from launch_ros.actions import Node


def generate_launch_description():
    return LaunchDescription([
        Node(
            package='learning_topic',
            executable='helloworld_topicpub_node',
        ),
        Node(
            package='learning_topic',
            executable='helloword_topicsub_node',
        ),
    ])

使用launch文件启动节点（以上两个节点我单独启动过，均没有问题）：

cd ~/ws/src/launch
ros2 launch simple.launch.py

会提示报错：

Failed to load entry point 'launch': No module named 'launch.launch_description_sources'
Traceback (most recent call last):
  File "/opt/ros/humble/bin/ros2", line 33, in <module>
    sys.exit(load_entry_point('ros2cli==0.18.7', 'console_scripts', 'ros2')())
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/cli.py", line 50, in main
    add_subparsers_on_demand(
  File "/opt/ros/humble/lib/python3.10/site-packages/ros2cli/command/__init__.py", line 237, in add_subparsers_on_demand
    extension = command_extensions[name]
KeyError: 'launch'

我更换了工作空间也不行，但是之前下载的一个课程文件（也是一个单独的工作空间）中的launch文件却能正常启动,一直找不到原因，请各位赐教。

附上我话题的setup文件：

from setuptools import find_packages, setup

package_name = 'learning_topic'

setup(
    name=package_name,
    version='0.0.0',
    packages=find_packages(exclude=['test']),
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='huang',
    maintainer_email='huang@todo.todo',
    description='TODO: Package description',
    license='TODO: License declaration',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
            'helloworld_topicpub_node   =   learning_topic.topic_publish:main',
            'helloworld_topicsub_node   =   learning_topic.topic_subscribe:main',
        ],
    },
)