Return a :class:`crtomo.grid.crt_grid` instance, with a debug grid that
    is distributed with the crtomo package. Multiple grids are available:

        * key=20 - a 20 electrode grid with 1m spacing, 4 elements between
          electrodes, rectangular elements.
        * key=40 - a 40 electrode grid with 1m spacing, 4 elements between
          electrodes, rectangular elements.

    Parameters
    ----------
    key: string
        key that identifies the grid


    Returns
    -------
    grid: :class:`crtomo.grid.crt_grid` instance
        loaded grid object

def get_grid(key):
    """Return a :class:`crtomo.grid.crt_grid` instance, with a debug grid that
    is distributed with the crtomo package. Multiple grids are available:

        * key=20 - a 20 electrode grid with 1m spacing, 4 elements between
          electrodes, rectangular elements.
        * key=40 - a 40 electrode grid with 1m spacing, 4 elements between
          electrodes, rectangular elements.

    Parameters
    ----------
    key: string
        key that identifies the grid


    Returns
    -------
    grid: :class:`crtomo.grid.crt_grid` instance
        loaded grid object

    """
    rbase = grid_files[key]
    elem_file = pk.resource_filename('crtomo', rbase['elem'])
    elec_file = pk.resource_filename('crtomo', rbase['elec'])

    grid = CRGrid.crt_grid(elem_file=elem_file, elec_file=elec_file)
    return grid