char type in Python messages is of type uint8_t not str.

[arjo129]

Bug report

Required Info:

• Operating System:
  • Ubuntu 22.04 and windows 10
• Installation type:
  • Binaries
• Version or commit hash:
  • Humble
• DDS implementation:
  • FastDDS
• Client library (if applicable):
  • rclpy

Steps to reproduce issue

The documentation page states that chars should corresponf to builtins.str but when I try to set a field of type char to a string in python like so:

my_awesome_msg.char_field = "L"

I get the error

AssertionError: The 'my_awesome_msg.char_field' field must be of type 'int'

Is the documentation wrong or is this unexepected behaviour?

I am willing to submit a fix for this.

[sloretz]

Thank you for the bug report! It seems like you're correct that the type should be a str field.

• ROS msg files to OMG IDL maps char to char: https://design.ros2.org/articles/mapping_dds_types.html
• OMG IDL char maps to python string with length 1: https://design.ros2.org/articles/idl_interface_definition.html

It seems like the bug is in rosidl_adapter. It maps ROS msg char to OMG IDL uint8:

rosidl/rosidl_adapter/rosidl_adapter/msg/__init__.py

Line 46 in 5d8191e

'char': 'uint8',

.

Would you be willing to open a PR with a fix on the rolling branch? I don't think we could backport it, but we could fix it going forward.