ROS 2 PyTerfaces IDL

Requirements	Compatibility	Tests
		Humble, Jazzy, Kilted ubuntu, windows

ROS 2 message and service definitions, metadata and serialization in Python.

Create new message types, (de)serialize them, compute the RIHS01 hash, and convert to and from ROS 2 Python messages. All ROS 2 common_interfaces are reimplemented, and every message tested to interoperate with ROS.

Table of Contents

• Install
• Reliability
• Example
  • Message
  • Service
  • Utilities
• Attribution
• Replicated ROS 2 Repos
  • Included Interfaces

Install

pip install ros2_pyterfaces[cyclone, cydr]

The library has three backends:

• core: normalized schema and message representation. This is plain Python, so you can easily do whatever you need. However, it cannot encode/decode.
• cyclone: This is the more complete IDL backend and the easiest one to hand-write. It is based on Cyclone DDS Python.
• cydr: This backend is much stricter about types and annotations, has some limitations, but is tremendously faster than Cyclone. It is based on cydr.

Examples for the same JointState message in each style:

• Core: ros2_pyterfaces/examples/core_joint_state.py
• Cyclone: ros2_pyterfaces/examples/cyclone_joint_state.py
• cydr: ros2_pyterfaces/examples/cydr_joint_state.py

Reliability

Each message type in this library is heavily tested, for a total of more than 4000 tests, including randomized roundtrips through ROS 2. The goal is 100% interoperability. Conversions, serialization, deserialization, hashes, and raw payload exchange, are all exercised against ROS 2.

Example

First, choose the layer that matches what you need. In this examples we use cyclone.

• core when you simply need a python dict.
• cyclone when you want a more ergonomic, all rounded dataclass.
• cydr when you want strict numpy types and higher performance.

Message

from dataclasses import dataclass, field
from ros2_pyterfaces.cyclone.idl import IdlStruct, types

@dataclass
class Time(IdlStruct, typename="builtin_interfaces/msg/Time"):
    sec: types.int32 = 0
    nanosec: types.uint32 = 0


@dataclass
class Header(IdlStruct, typename="std_msgs/msg/Header"):
    stamp: Time = field(default_factory=Time)
    frame_id: str = ""

@dataclass
class JointState(IdlStruct, typename="sensor_msgs/msg/JointState"):
    header: Header = field(default_factory=Header)
    name: types.sequence[str] = field(default_factory=list)
    position: types.sequence[types.float64] = field(default_factory=list)
    velocity: types.sequence[types.float64] = field(default_factory=list)
    effort: types.sequence[types.float64] = field(default_factory=list)

my_msg: JointState = JointState(
    header=Header(
        stamp=Time(sec=1, nanosec=2),
        frame_id="base_link",
    ),
    name=["joint_1", "joint_2"],
    position=[1.0, 2.0],
    velocity=[0.1, 0.2],
    effort=[0.0, 0.0],
)

# serialization
blob_bytes: bytes = my_msg.serialize()
my_msg_again: JointState = JointState.deserialize(blob_bytes)

# ROS 2 metadata
json_type_description = JointState.json_type_description()
ros_hash = JointState.hash_rihs01()

# ROS 2 conversion
ros_msg_type = JointState.to_ros_type()
ros_msg = my_msg.to_ros()
our_msg: JointState = JointState.from_ros(ros_msg)

Service

Services follow the ROS naming pattern: *_Request, *_Response, *_Event, plus a small wrapper type. The serializable types are the request, response, and service wrapper. With cyclone, the generated event type is also a usable IDL struct. With cydr, the event type is just a placeholder because unsuported. The top-level service type is usually created with make_idl_service(...). If you omit event_type=... (most cases), the factory generates the matching service metadata for you.

from dataclasses import dataclass
from ros2_pyterfaces.cyclone import idl

# Same classes definition as Messages for *_Request *_Response
@dataclass
class SetBool_Request(idl.IdlStruct, typename="std_srvs/srv/SetBool_Request"):
    data: bool = False


@dataclass
class SetBool_Response(idl.IdlStruct, typename="std_srvs/srv/SetBool_Response"):
    success: bool = False
    message: str = ""

# Top-level service type
SetBool = idl.make_idl_service(SetBool_Request, SetBool_Response)

# Serialization
some_request: SetBool_Request = SetBool.Request(data=True)
some_response: SetBool_Response = SetBool.Response(success=True, message="yey")

# ROS 2 metadata
json_type_description = SetBool.json_type_description()
ros_hash = SetBool.hash_rihs01()

# ROS 2 conversion
ros_srv_type = SetBool.to_ros_type()

ros_request = some_request.to_ros()
request_again = SetBool.Request.from_ros(ros_request)

ros_response = some_response.to_ros()
response_again = SetBool.Response.from_ros(ros_response)

Utilities

Messages can be converted to the normalized core representation (a json style dict of str, int, bytes, and list) for comparisons, tests, snapshots, and easier processing:

core_schema = type(my_msg).to_core_schema()
core_msg = my_msg.to_core_message()

same_msg_again = type(my_msg).from_core_message(core_msg)
assert same_msg_again.to_core_message() == core_msg

The same core schema and core message can also be passed through ros2_pyterfaces.core helpers when you want ROS conversion without depending on a specific IDL backend.

Attribution

Dependencies By Backend

• core
  • NumPy
  • ROS 2 Python message/service classes from the installed distro, when using ROS conversion helpers
• cyclone
  • Cyclone DDS Python via cyclonedds_idl
• cydr
  • cydr
  • msgspec

Replicated ROS 2 Messages Repos

• common_interfaces
• rcl_interfaces
• unique_identifier_msgs

Included Interfaces

• ros2_pyterfaces.cyclone.builtin_interfaces: msg.py
• ros2_pyterfaces.cyclone.composition_interfaces: srv.py
• ros2_pyterfaces.cyclone.diagnostic_msgs: msg.py, srv.py
• ros2_pyterfaces.cyclone.geometry_msgs: msg.py
• ros2_pyterfaces.cyclone.lifecycle_msgs: msg.py, srv.py
• ros2_pyterfaces.cyclone.nav_msgs: msg.py, srv.py
• ros2_pyterfaces.cyclone.rcl_interfaces: msg.py, srv.py
• ros2_pyterfaces.cyclone.rosgraph_msgs: msg.py
• ros2_pyterfaces.cyclone.sensor_msgs: msg.py, srv.py
• ros2_pyterfaces.cyclone.service_msgs: msg.py
• ros2_pyterfaces.cyclone.shape_msgs: msg.py
• ros2_pyterfaces.cyclone.statistics_msgs: msg.py
• ros2_pyterfaces.cyclone.std_msgs: msg.py
• ros2_pyterfaces.cyclone.std_srvs: srv.py
• ros2_pyterfaces.cyclone.stereo_msgs: msg.py
• ros2_pyterfaces.cyclone.test_msgs: msg.py
• ros2_pyterfaces.cyclone.type_description_interfaces: msg.py, srv.py
• ros2_pyterfaces.cyclone.trajectory_msgs: msg.py
• ros2_pyterfaces.cyclone.unique_identifier_msgs: msg.py
• ros2_pyterfaces.cyclone.visualization_msgs: msg.py, srv.py