setting env_var in config block

I have this config block in which there is a database field set using env_var macros. I have tried couple syntax but I still get an error. Here is the latest test. Notice that I have an underscore before the env vars to separate the tokens. I have tried using spaces but I get the same.

        database= "env_var('DB_PREFIX')_env_var('DB_ENV')_ANALYTICS_LZ",
        unique_key=['dv_impression_id', '_data_version']