code: def env_valid(env):
    
    if env not in EFConfig.ENV_LIST:
      raise ValueError("unknown env: {}; env must be one of: ".format(env) + ", ".join(EFConfig.ENV_LIST))
    return True
docs: Given an env, determine if it's valid
    Args:
      env: the env to check
    Returns:
      True if the env is valid
    Raises:
      ValueError with message if the env is not valid