question: How to define an interval validate callbacks in lightning
context: I want to train my model in 20000 steps and run evaluation on each 1000 steps
  I try to define the callback like this:
  class IntervalStepValidate(Callback):
      def __init__(self, config):
          self.config = config
          self.total_steps = 20000
          self.validation_interval = 1000
  
      def on_batch_end(self, trainer, pl_module):
          if self.total_steps % self.validation_interval == 0:
              trainer.run_evaluation()
  
  But I find out that there is no run_evaluation() in the latest version of Pytorch-Lightning :(
  How can I update this code to get the function I want?
answer: there is a val_check_interval argument for it inside Trainer. You can set Trainer(val_check_interval=1000).