Hi, first of all thank you for this wonderful library. I recently implemented Python bindings for my own use and saw in issue #248 that an interface with Python could be useful for the community. The Python bindings / interface is done with pybind11 a mature and efficient open-source binding library that integrates well with ROS. For the moment I have only bound public functions of the grid_map_core::GridMap class (and their immediate dependencies) but more could easily be added, let me know.

Main changes

New package grid_map_python that will contain all the bindings containing:
- py_module.cpp and py_core.cpp that generate the bindings library
- A setup.py and src/grid_map/__init__.py that expose the module
- A tests folder containing scripts to test bound functions from Python
Interface with ROS messages: two from_msg and to_msg functions to bridge the bound object with native Python grid_map_msgs/GridMap structures.

Exemple of usage

Using a GridMap object in a Python scripts is simply a matter of importing it from the grid_map module and calling its functions as with any Python object:

from grid_map import GridMap
a = GridMap(['elevation', 'intensity', 'roughness'])
a.setGeometry([1,2], 0.5, [3, 10])
print(a)
# <1.00x2.00x0.50 grid on ['elevation', 'intensity', 'roughness'] at [ 3. 10.]>

a['elevation'][0,1:2] = 1
print(a['elevation'])
# [[nan,  1., nan, nan],
#  [nan, nan, nan, nan]]

Eigen matrices are exposed as numpy arrays (or compatibles) and vice-versa, making the use of GridMap frunctions straight-forward.

I have been using this for the past month and saw no performance issues or big limitations. The bindings are still incomplete but I think that partial coverage is better than no coverage. If people find it important to add other modules or class to the bindings, they can easily be added afterwards.