make if statements cleaner for prepare_inputs_for_generation

src/transformers/modeling_ctrl.py

@@ -491,8 +491,9 @@ class CTRLLMHeadModel(CTRLPreTrainedModel):
         return self.lm_head
 
     def prepare_inputs_for_generation(self, input_ids, **kwargs):
-        # inputs_ids should only be composed of last token if past is in kwargs and defined
-        input_ids = input_ids[:, -1].unsqueeze(-1) if 'past' in kwargs and kwargs['past'] else input_ids
+        # only last token for inputs_ids if past is defined in kwargs
+        if 'past' in kwargs and kwargs['past']:
+            input_ids = input_ids[:, -1].unsqueeze(-1)
 
         inputs = {"input_ids": input_ids}
         inputs.update(kwargs)