gz-transport: Python Support

[azeey-test]

Configuration

• os: Windows

Links

• Live
• Source

Process

Step 1 - Instructions work

Step 2 - Images (if there are any) match the result

[peci1]

I'll test this over the weekend on a real Win 10 laptop.

[peci1]

I couldn't get Python support to work on Windows.

I had to install protobuf, as only libprotobuf is installed according to the win install tutorial. This decreases libprotobuf version to 4.* from 5.*, as protobuf is only available in version 4.* . I rebuilt the workspace after this downgrade.

Now I see:

 λ dir D:\programming\gz9-ws\gz-ws\install\lib\python\gz\transport14
 Directory of D:\programming\gz9-ws\gz-ws\install\lib\python\gz\transport14

15.09.2024  23:28    <DIR>          .
15.09.2024  23:28    <DIR>          ..
15.09.2024  23:02           255 488 _transport.cp312-win_amd64.pyd
15.09.2024  23:28             5 529 __init__.py

I set PYTHONPATH to

set PYTHONPATH=D:\programming\gz9-ws\gz-ws\install\lib\python;D:\programming\gz9-ws\conda\Lib\site-packages

When I run the example, I get the following error:

λ python publisher.py
Traceback (most recent call last):
  File "D:\programming\gz9-ws\gz-ws\src\gz-transport\python\examples\publisher.py", line 19, in <module>
    from gz.transport14 import Node
  File "D:\programming\gz9-ws\gz-ws\install\lib\python\gz\transport14\__init__.py", line 16, in <module>
    from ._transport import Node as _Node
ImportError: DLL load failed while importing _transport: module not found

I've inspected the pyd file with Depends and nothing seems to be missing.

I can't continue with this here. Any thoughts, @traversaro?

[traversaro]

Just a curiosity, why do you need protobuf? Anyhow, I think the problem is that Python on Windows by default ignores the PATH env variable when loading extensions (see robotology/robotology-superbuild#1268 and the linked issue for some references).

Possible solution are calling set CONDA_DLL_SEARCH_MODIFICATION_ENABLE=1 before launching python or call os.add_dll_directory with the directory of the location where the .dll of gZ-transport are stored.

[peci1]

Just a curiosity, why do you need protobuf?

Because of the content of the generated .py files from gz-msgs, e.g.

#file gz/msgs/stringmsg_pb2.py
from google.protobuf import descriptor as _descriptor
...

Possible solution are calling set CONDA_DLL_SEARCH_MODIFICATION_ENABLE=1 before launching python

Did not help.

call os.add_dll_directory with the directory of the location where the .dll of gZ-transport are stored.

Did help! Now I can run the tutorial.

import os
os.add_dll_directory("D:\\programming\\gz9-ws\\gz-ws\\install\\bin")
from ._transport import Node as _Node

[peci1]

I've reported the issue: gazebosim/gz-transport#538 .

[peci1]

A little improvement in gazebosim/gz-transport#539 .

Required install tutorial change: gazebosim/docs#516 .

Requires gazebosim/gz-transport#538 to be fixed.

After the referenced PRs/issues are done, this tutorial works as it should.