Roll out new particle property getters in the Python interface

[jngrad]

The Python interface should reflect the recent changes to the Particle struct. The goal is to adapt all property getters to the new syntax, except for ext_flag and rotation which can be ignored (they rely on special getters outside the class definition). The setters don't need to change. This task is suitable for a coding day and can be done in about half an hour. No C++ knowledge required.

The src/python/espressomd/particle_data.pyx file currently looks like this:

cdef class ParticleHandle:
    property type:
        def __get__(self):
            self.update_particle_data()
            return self.particle_data.p.type

It should look like this:

cdef class ParticleHandle:
    property type:
        def __get__(self):
            self.update_particle_data()
            return self.particle_data.type()  # <<< now we simply call the struct method

To achieve this, the src/python/espressomd/particle_data.pxd needs to be changed from this:

cdef extern from "particle_data.hpp":
    ctypedef struct particle_properties "ParticleProperties":
        int    identity
        int    type

    ctypedef struct particle "Particle":
        particle_properties p
        Vector3d calc_dip()

to this:

cdef extern from "particle_data.hpp":
    ctypedef struct particle_properties "ParticleProperties":
        int    identity  # <<< 'type' is gone, 'identity' can be removed too

    ctypedef struct particle "Particle":
        particle_properties p
        Vector3d calc_dip()
        int type()  # <<< struct method is declared, do the same for all other properties

The same changes have to be applied to 2-3 lines in src/python/espressomd/visualization_mayavi.pyx.

Once all getters are replaced, particle_data.pxd should no longer need to declare the particle substructs.

[jngrad]

Additional task: do the same for compiler-dependent getters. All particle properties should now be available, even when features are not compiled in (when in doubt, run the python testsuite with maintainer/configs/empty.hpp as myconfig.hpp). Go from:

cdef extern from "particle_data.hpp":
    ctypedef struct particle "Particle":
        particle_properties p
        Vector3d calc_dip()

    IF ROTATIONAL_INERTIA:
        void set_particle_rotational_inertia(int part, const Vector3d & rinertia)
        Vector3d get_particle_rotational_inertia(const particle * p)

To this (and adapt the .pyx file accordingly):

cdef extern from "particle_data.hpp":
    ctypedef struct particle "Particle":
        particle_properties p
        Vector3d calc_dip()
        Vector3d rinertia()  # <<< struct method is declared

    IF ROTATIONAL_INERTIA:
        void set_particle_rotational_inertia(int part, const Vector3d & rinertia)
        # old getter is gone

The getters that are removed from the Cython file can also be removed from src/core/particle_data.hpp.

[christophlohrmann]

can do