Investigate using python bindings of sdformat instead of the gz command line

[diegoferigo]

Starting from version 13, sdformat introduced native Python bindings. It's worth investigating if we could just call this library (that depends only on sdformat) instead of requiring to find the entire Gazebo Classic or Gazebo Sim suite.

Few comments:

• I could not find any package in PyPI nor conda-forge, last time I tried I think I installed it from the OSRF repo.
• Relevant discussion in Add lxml dependency jaxsim#89 (comment)

[traversaro]

I could not find any package in PyPI nor conda-forge, last time I tried I think I installed it from the OSRF repo.

There is indeed no package on PyPI. On conda-forge the package are sdformat13-python and sdformat14-python, see https://github.com/conda-forge/libsdformat-feedstock and ami-iit/jaxsim#89 (comment) .

[diegoferigo]

Excellent, maybe instead of replacing the usage of gz|ign command line, we can first try to import sdformatXX and, if not found, use the existing logic that exploits the full Gazebo installation.

In this way, we can slim down significantly our conda environments that install a full Gazebo suite just for having gz sdf.

[traversaro]

Excellent, maybe instead of replacing the usage of gz|ign command line, we can first try to import sdformatXX and, if not found, use the existing logic that exploits the full Gazebo installation.

In this way, we can slim down significantly our conda environments that install a full Gazebo suite just for having gz sdf.

Yes, that probably gets the best of both worlds, all dependencies installed in conda-forge while the possibility still of installing the library via pip by relying on gz installed in the system.

[diegoferigo]

Referring #34 (comment), we managed to perform the URDF to SDF conversion by only requiring sdformat and gz-tools. I had early attempts of using the Python bindings of sdformat, but I couldn't find any way to catch the stdout produced when the conversion fails. For unknown reasons, the usual Python pipes to redirect the output do not catch the failures.

I'll leave this issue open as help wanted in case someone wants to try again (and I mean, using the python bindings as alternative method not as replacement). In the meantime, I can live happy by calling gz sdf.