Check tokenize params on DPOTrainer (huggingface#1197)

* Check if tokenizer and max len params are None

* Update warning messages for missing parameters

trl/trainer/dpo_trainer.py

@@ -276,34 +276,32 @@ def make_inputs_require_grad(module, input, output):
         else:
             self.ref_model = create_reference_model(model)
 
-        if data_collator is None:
-            if tokenizer is None:
-                raise ValueError(
-                    "max_length or a tokenizer must be specified when using the default DPODataCollatorWithPadding"
-                )
-            if max_length is None:
-                warnings.warn(
-                    "When using DPODataCollatorWithPadding, you should set `max_length` in the DPOTrainer's init"
-                    " it will be set to `512` by default, but you should do it yourself in the future.",
-                    UserWarning,
-                )
-                max_length = 512
-            if max_prompt_length is None:
-                warnings.warn(
-                    "When using DPODataCollatorWithPadding, you should set `max_prompt_length` in the DPOTrainer's init"
-                    " it will be set to `128` by default, but you should do it yourself in the future.",
-                    UserWarning,
-                )
-                max_prompt_length = 128
+        if tokenizer is None:
+            raise ValueError("tokenizer must be specified to tokenize a DPO dataset.")
+        if max_length is None:
+            warnings.warn(
+                "`max_length` is not set in the DPOTrainer's init"
+                " it will default to `512` by default, but you should do it yourself in the future.",
+                UserWarning,
+            )
+            max_length = 512
+        if max_prompt_length is None:
+            warnings.warn(
+                "`max_prompt_length` is not set in the DPOTrainer's init"
+                " it will default to `128` by default, but you should do it yourself in the future.",
+                UserWarning,
+            )
+            max_prompt_length = 128
 
-            if max_target_length is None and self.is_encoder_decoder:
-                warnings.warn(
-                    "When using DPODataCollatorWithPadding with an encoder decoder architecture, you should set `max_target_length` in the DPOTrainer's init"
-                    " it will be set to `128` by default, but you should do it yourself in the future.",
-                    UserWarning,
-                )
-                max_target_length = 128
+        if max_target_length is None and self.is_encoder_decoder:
+            warnings.warn(
+                "When using an encoder decoder architecture, you should set `max_target_length` in the DPOTrainer's init"
+                " it will default to `128` by default, but you should do it yourself in the future.",
+                UserWarning,
+            )
+            max_target_length = 128
 
+        if data_collator is None:
             data_collator = DPODataCollatorWithPadding(
                 pad_token_id=tokenizer.pad_token_id,
                 label_pad_token_id=label_pad_token_id,