def _initialize_attributes(self):
        assert "nc" not in self.__dict__.keys(), \
            "NetCdf._initialize_attributes() error: nc attribute already set"

        self.nc_epsg_str = 'epsg:4326'
        self.nc_crs_longname = "http://www.opengis.net/def/crs/EPSG/0/4326"
        self.nc_semi_major = float(6378137.0)
        self.nc_inverse_flat = float(298.257223563)

        self.global_attributes = {}

        self.fillvalue = FILLVALUE

        # initialize attributes
        self.grid_crs = None
        self.zs = None
        self.ys = None
        self.xs = None

        self.chunks = {"time": None}
        self.chunks["x"] = int(self.shape[1] / 4) + 1
        self.chunks["y"] = int(self.shape[2] / 4) + 1
        self.chunks["z"] = self.shape[0]
        self.chunks["layer"] = self.shape[0]

        self.nc = None

        self.origin_x = None
        self.origin_y = None
private method to initial the attributes
dataset/ETHPy150Open modflowpy/flopy/flopy/export/netcdf.py/NetCdf._initialize_attributes