Issue reading radolan bin.bz2 file

[Kedharkb]

Hello i am trying to read the file from this url https://opendata.dwd.de/weather/radar/radolan/ry/raa01-ry_10000-latest-dwd---bin.bz2 follwing the example from https://github.com/wradlib/wradlib-notebooks/, but i am facing the OSError: 'WRADLIB_DATA' environment variable not set. Can someone please let me know how to set the WRADLIB_DATA env var.
Please refer to the following code.

def download_and_read_RY(RY_timestamp):. 
    rw_filename = wrl.util.get_wradlib_data_file(
    "radolan/misc/raa01-rw_10000-1408102050-dwd---bin.gz")
download_and_read_RY("latest")