def __init__(self, url=None):
if url is None:<EOL><INDENT>url = os.environ.get('<STR_LIT>', '<STR_LIT>')<EOL><DEDENT>self.http = HTTPClient(url)<EOL>
Args:
    target (string): the device url

If target is None, device url will set to env-var "DEVICE_URL" if defined else set to "http://localhost:8100"