Fix checkpoint warning for floats
#1819 added this warning when saving checkpoints. 
  
    
      pytorch-lightning/pytorch_lightning/callbacks/model_checkpoint.py
    
    
        Lines 259 to 263
      in
      bd49b07
    
  
  
    

        
          
           if not isinstance(current, torch.Tensor): 
        

        
          
               rank_zero_warn( 
        

        
          
                   f'The metric you returned {current} must be a Torch.Tensor instance, checkpoint not saved ' 
        

        
          
                   f'HINT: what is the value of {self.monitor} in validation_end()?', RuntimeWarning 
        

        
          
               ) 
        
    
  



Is there a reason why native Python floats aren't supported? I think it's actually quite common especially when libraries e.g. scipy are involved when computing the metrics.
It says checkpoint not saved, but actually checkpoints are still saved. This check doesn't actually change the saving logic besides giving that warning.