some confusion about Evaluator

May I ask why the author is in the class Evaluator:

def __init__(self, cwd: str, env, args: Config, if_tensorboard: bool = False):

self.cwd = cwd # current working directory to save model

self.env = env # the env for Evaluator, `eval_env = env` in default

self.agent_id = args.gpu_id

self.total_step = 0 # the total training step

self.start_time = time.time() # `used_time = time.time() - self.start_time`

self.eval_times = args.eval_times # number of times that get episodic cumulative return

self.eval_per_step = args.eval_per_step # evaluate the agent per training steps

_**_self.eval_step_counter = -self.eval_per_step # `self.total_step > self.eval_step_counter + self.eval_per_step`
Here self.eval_step_counter= -self.eval_per_step is selected and self.eval_step_counter=0 in hellow dqn_**_