get/set_material_database() for WG/Circ etc.

Here's the code from Device.py, which works. Also need to set self.matDB = None in __init__() constructor.

    def set_material_database(self, path):
    '''Set the path to the material database (*.mat) file.  Only needed if you are defining materials using this database ('mat'/material type waveguides instead of 'rix'/refractive index).  This sets a materials file that will be used only by this Device.  
    Although waveguide nodes can specify their own (different) materials files, it is recommended that a global file be used instead since FimmProp Devices do not accept multiple materials files (to avoid confusion and identically-named materials from different files).  The single global file can be set to `include` any other materials files.

    Parameters
    ----------
    path : string
        Absolute or relative path to the material database file.  `path` will be automatically converted to an absolute path, as a workaround to a FimmProp Device Node bug that causes it to only accept absolute paths.
        '''
    import os
    path = os.path.abspath(path)    # convert to absolute path
    if os.path.isfile(path):
        self.matDB = str(path)
        fimm.Exec(   self.nodestring + '.setmaterbase(%s)'%(self.matDB)   )
    else:
        ErrStr = "Material database file does not exist at the specified path `%s`" %(path)
        raise IOError(ErrStr)
    if DEBUG(): print "Device '%s'.matDB = "%(self.name), self.matDB

def get_material_database(self,):
    '''Get path to this Device's material database file.

    Returns
    -------
    path : string
        Absolute path to the material database file used by this node.
        '''
    try:
        self.matDB
    except:
        if DEBUG(): print "unset global_matDB --> None"
        self.matDB = fimm.Exec(   self.nodestring + '.materbasename()'   )
    return self.matDB

demisjohn / pyFIMM

get/set_material_database() for WG/Circ etc. #83