[WIP] [Python Bindings] Changed Vector/Matrix map to Python objects

[francesco-romano]

tl;dr; instead of using Python function to generate and parse string to convert between types, we now use native C code.

This might have an impact on current Python code. For sure, it will require some modifications:

• removed the helper functions as they are no longer needed
• renamed fromList to fromPython (as it now accepts both lists and Numpy arrays).

Tests are missing. I do not have the bandwidth to implement them.
Let me know what do you think - if something is missing.

Of course, waiting for travis to catch all the bugs 😄

[francesco-romano]

@traversaro not sure I need to include all these files. For example, I forgot to include Wrench.h, etc. and it seems to work.

[traversaro]

cc @diegoferigo @anqingd and all the Python users around.

[traversaro]

There are a few users of the iDynTree's Python API . I would like to implement proper deprecation of the old APIs before removing them.

[francesco-romano]

Should be enough to add a fromList that maps to fromPython I think. It can be done in the old init_helpers. While the old init_numpy_helpers can become a simple noop (pass)

[francesco-romano]

While working on some tests, I realised the PR is not ready as fromPython should be a sort of factory method, while now it is a simple method acting on an already-built object.

[francesco-romano]

Can somebody run the python tests?
I tried with:

• Python 2.7.10 (default on my Mac 10.13.6) and I get a SegFault
• Python 2.7.11 (on travis) same error as before
• Python 2.7.13 and it works

[traversaro]

Handy recap of Python version on different systems: https://repology.org/metapackage/python2/versions .

[diegoferigo]

I tried a rebased version of this branch on Ubuntu 18.04 with Python 3.6 and I've got the following failures:

The following tests FAILED:
         51 - PythonHelperTests (SEGFAULT)
         52 - PythonDeprecatedTests (SEGFAULT)

After a quick execution in the interpreter of the additional binded methods I discovered that fromNumpy() and toNumpy() work well. The segfault seems due the methods that use regular python lists.

cc @francesco-romano @traversaro

[francesco-romano]

Happy if you are able to rebase this and merge it. It has remained here for far too long.

This problem does not look new to me. I am sure I read something similar recently somewhere. I think there has been some changes to Python lists in some 3.x version. Hopefully I will find again the discussion

[traversaro]

@diegoferigo Did you worked on this recently as part of the development of Python-based controllers?

[diegoferigo]

@traversaro I am using a rebased version of this branch since some while without any problem. Though, segfaults without any errors occur if they're not used correctly, and debugging these problems can be challenging in a Python project. I think this PR is a great start, but it needs some polishing to become stable enough.

I keep postponing this activity due to other priorities, but I have to do it before releasing the first stable release of gym-ignition in any case.

[traversaro]

As this PR is currently stale, I will close it, but feel free to re-open it if someone wants to work on this, thanks!

[diegoferigo]

@traversaro what I wrote in #484 (comment) is still valid. I will open a new PR as soon as I manage to clean it.