Add lxml dependency

[giotherobot]

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📚 Documentation preview 📚: https://jaxsim--89.org.readthedocs.build//89/

[flferretti]

LGTM

[diegoferigo]

Good catch @giotherobot, thanks for the contribution. Can you please add lxml also to environment.yml?

[giotherobot]

There are still some dependencies missing to run python -m jaxsim.mujoco: gz or ign in the path, solved by installing libgz-sim7 as suggested by @flferretti and resolve_robotics_uri_py.

[diegoferigo]

There are still some dependencies missing to run python -m jaxsim.mujoco: gz or ign in the path, solved by installing libgz-sim7 as suggested by @flferretti and resolve_robotics_uri_py.

Yep, that's right. Those are system dependencies that are expected to be found in the system in the case jaxsim is installed from PyPI. However, in a conda environment, we can specify them as [viz] dependencies.

@flferretti on the long term, we should consider to add them as rod dependencies. Especially in recent Gazebo Sim versions having python bindings of sdformat. Last time I checked, it was not yet part of conda-forge. Maybe now it is.

[flferretti]

Yep, that's right. Those are system dependencies that are expected to be found in the system in the case jaxsim is installed from PyPI. However, in a conda environment, we can specify them as [viz] dependencies.

@flferretti on the long term, we should consider to add them as rod dependencies. Especially in recent Gazebo Sim versions having python bindings of sdformat. Last time I checked, it was not yet part of conda-forge. Maybe now it is.

libsdformat on conda-forge provides sdformat14-python

[traversaro]

I guess the tricky aspect is that sdformat is not on PyPI, and I am not sure if it will ever be there. Probably we can fallback to the gz command if the sdformat python module can't be found?

[flferretti]

I guess the tricky aspect is that sdformat is not on PyPI, and I am not sure if it will ever be there.

@traversaro isn't it python-sdformat?

Probably we can fallback to the gz command if the sdformat python module can't be found?

This looks good, so we are not forced to use gazebo

[diegoferigo]

I guess the tricky aspect is that sdformat is not on PyPI, and I am not sure if it will ever be there.

@traversaro isn't it python-sdformat?

Nope, that's a third-party project, not what @traversaro meant.

I guess the tricky aspect is that sdformat is not on PyPI, and I am not sure if it will ever be there. Probably we can fallback to the gz command if the sdformat python module can't be found?

Yep this can be done. When I tried many months ago, what I didn't like of the plain python bindings of sdformat is that I could not manage to get a proper error in stdout if the input URDF or SDF is malformed. Calling gz instead provides clear error messages. Not sure if something has changed since.

[traversaro]

When I tried many months ago, what I didn't like of the plain python bindings of sdformat is that I could not manage to get a proper error in stdout if the input URDF or SDF is malformed. Calling gz instead provides clear error messages. Not sure if something has changed since.

If you have time, it would be useful to report this upstream in https://github.com/gazebosim/sdformat, Python bindings of sdformat and gz libraries in general to not have a lot of users at the moment, so feedback from actual users of the bindings is quite precious for sdformat upstream developers.