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Migrating Python Packages

Build tool

Instead of using catkin_make, catkin_make_isolated or catkin build ROS 2 uses the command line tool colcon to build and install a set of packages. See the beginner tutorial to get started with colcon.

Build system

For pure Python packages, ROS 2 uses the standard setup.py installation mechanism familiar to Python developers.

Update the files to use setup.py

If the ROS 1 package uses CMake only to invoke the setup.py file and does not contain anything beside Python code (e.g. no messages, services, etc.) it should be converted into a pure Python package in ROS 2:

  • Update or add the build type in the package.xml file:

    <export>
      <build_type>ament_python</build_type>
    </export>
    
  • Remove the CMakeLists.txt file

  • Update the setup.py file to be a standard Python setup script

ROS 2 supports Python 3 only. While each package can choose to also support Python 2 it must invoke executables with Python 3 if it uses any API provided by other ROS 2 packages.

Update source code

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'

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

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

Creating a Publisher

In ROS 1:

pub = rospy.Publisher('chatter', String)
# or
pub = rospy.Publisher('chatter', String, queue_size=10)

In ROS 2:

pub = node.create_publisher(String, 'chatter', rclpy.qos.QoSProfile())
# or
pub = node.create_publisher(String, 'chatter', 10)

Creating a Subscriber

In ROS 1:

sub = rospy.Subscriber('chatter', String, callback)
# or
sub = rospy.Subscriber('chatter', String, callback, queue_size=10)

In ROS 2:

sub = node.create_subscription(String, 'chatter', callback, rclpy.qos.QoSProfile())
# or
sub = node.create_subscription(String, 'chatter', callback, 10)

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)