You're reading the documentation for an older, but still supported, version of ROS 2. For information on the latest version, please have a look at Galactic.

Python migration guide from ROS 1

Node Initialization

In ROS 1:

rospy.init_node('asdf')

rospy.loginfo('Created node')

In ROS 2:

rclpy.init(args=sys.argv)
node = rclpy.create_node('asdf')

node.get_logger().info('Created node')

ROS Parameters

In ROS 1:

 port = rospy.get_param('port', '/dev/ttyUSB0')
 assert isinstance(port, str), 'port parameter must be a str'

 buadrate = rospy.get_param('baudrate', 115200)
 assert isinstance(port, int), 'port parameter must be an integer'

rospy.logwarn('port: ' + port)

In ROS 2:

port = node.declare_parameter('port', '/dev/ttyUSB0').value
assert isinstance(port, str), 'port parameter must be a str'

baudrate = node.declare_parameter('baudrate', 115200).value
assert isinstance(port, int), 'port parameter must be an integer'

node.get_logger().warn('port: ' + port)

Creating a Publisher

In ROS 1:

pub = rospy.Publisher('chatter', String)

In ROS 2:

pub = node.create_publisher(String, 'chatter')

Creating a Subscriber

In ROS 1:

sub = rospy.Subscriber('chatter', String, callback)

In ROS 2:

sub = node.create_subscription(String, 'chatter', callback)

Creating a Service

In ROS 1:

srv = rospy.Service('add_two_ints', AddTwoInts, add_two_ints_callback)

In ROS 2:

srv = node.create_service(AddTwoInts, 'add_two_ints', add_two_ints_callback)

Creating a Service Client

In ROS 1:

rospy.wait_for_service('add_two_ints')
add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)
resp = add_two_ints(req)

In ROS 2:

add_two_ints = node.create_client(AddTwoInts, 'add_two_ints')
while not add_two_ints.wait_for_service(timeout_sec=1.0):
    node.get_logger().info('service not available, waiting again...')
resp = add_two_ints.call_async(req)
rclpy.spin_until_future_complete(node, resp)