repetiton_penalty and logits_bias just using logits_processors (#1004)

* refactor of repetition_penalty and logits_bias to use logits_processor

* nits

---------

Co-authored-by: Awni Hannun <awni@apple.com>

llms/mlx_lm/utils.py

@@ -101,7 +101,7 @@ def get_model_path(path_or_hf_repo: str, revision: Optional[str] = None) -> Path
     return model_path
 
 
-def apply_repetition_penalty(logits: mx.array, generated_tokens: Any, penalty: float):
+def apply_repetition_penalty(logits: mx.array, tokens: mx.array, penalty: float):
     """
     Apply repetition penalty to specific logits based on the given context.
 
@@ -109,19 +109,18 @@ def apply_repetition_penalty(logits: mx.array, generated_tokens: Any, penalty: f
 
     Args:
         logits (mx.array): The logits produced by the language model.
-        generated_tokens (any): A list of N previous tokens.
+        tokens (mx.array): A list of N previous tokens.
         penalty (float): The repetition penalty factor to be applied.
 
     Returns:
         logits (mx.array): Logits with repetition penalty applied to generated tokens.
     """
-    if len(generated_tokens) > 0:
-        indices = mx.array([token for token in generated_tokens])
-        selected_logits = logits[:, indices]
+    if len(tokens) > 0:
+        selected_logits = logits[:, tokens]
         selected_logits = mx.where(
             selected_logits < 0, selected_logits * penalty, selected_logits / penalty
         )
-        logits[:, indices] = selected_logits
+        logits[:, tokens] = selected_logits
     return logits
 
 
@@ -158,7 +157,7 @@ def generate_step(
     max_kv_size: Optional[int] = None,
     cache_history: Optional[List[Tuple[mx.array, mx.array]]] = None,
     logit_bias: Optional[Dict[int, float]] = None,
-    logits_processor: Optional[Callable[[mx.array, mx.array], mx.array]] = None,
+    logits_processor: Optional[List[Callable[[mx.array, mx.array], mx.array]]] = None,
 ) -> Generator[Tuple[mx.array, mx.array], None, None]:
     """
     A generator producing token ids based on the given prompt from the model.
@@ -182,8 +181,8 @@ def generate_step(
         max_kv_size (int, optional): Maximum size of the key-value cache. Old
           entries (except the first 4 tokens) will be overwritten.
         logit_bias (dictionary, optional): Additive logit bias.
-        logits_processor (Callable[[mx.array, mx.array], mx.array], optional):
-            A function that takes tokens and logits and returns the processed
+        logits_processor (List[Callable[[mx.array, mx.array], mx.array]], optional):
+            A list of functions that take tokens and logits and return the processed
             logits. Default: ``None``.
 
     Yields:
@@ -213,6 +212,27 @@ def generate_step(
             f"repetition_penalty must be a non-negative float, got {repetition_penalty}"
         )
 
+    logits_processor = logits_processor or []
+
+    if repetition_penalty:
+
+        def repetition_penalty_processor(tokens, logits):
+            return apply_repetition_penalty(
+                logits, tokens[-repetition_context_size:], repetition_penalty
+            )
+
+        logits_processor.append(repetition_penalty_processor)
+
+    if logit_bias:
+        indices = mx.array(list(logit_bias.keys()))
+        values = mx.array(list(logit_bias.values()))
+
+        def logit_bias_processor(_, logits):
+            logits[:, indices] += values
+            return logits
+
+        logits_processor.append(logit_bias_processor)
+
     y = prompt
     tokens = None
 
@@ -229,40 +249,18 @@ def generate_step(
             c.update_and_fetch(h[0], h[1])
         mx.eval([c.state for c in cache])
 
-    repetition_context = prompt.tolist()
-
-    if repetition_context_size:
-        repetition_context = repetition_context[-repetition_context_size:]
-
-    if logit_bias:
-        indices = mx.array(list(logit_bias.keys()))
-        values = mx.array(list(logit_bias.values()))
-
     def _step(y):
-        nonlocal repetition_context
         logits = model(y[None], cache=cache)
         logits = logits[:, -1, :]
 
         if logits_processor:
             nonlocal tokens
             tokens = mx.concat([tokens, y]) if tokens is not None else y
-            logits = logits_processor(tokens, logits)
 
-        if logit_bias:
-            logits[:, indices] += values
+            for processor in logits_processor:
+                logits = processor(tokens, logits)
 
-        if repetition_penalty:
-            logits = apply_repetition_penalty(
-                logits, repetition_context, repetition_penalty
-            )
         y, logprobs = sample(logits)
-            repetition_context.append(y.item())
-        else:
-            y, logprobs = sample(logits)
-
-        if repetition_context_size:
-            if len(repetition_context) > repetition_context_size:
-                repetition_context = repetition_context[-repetition_context_size:]
         return y, logprobs.squeeze(0)
 
     while y.size > prefill_step_size:

llms/tests/test_generate.py

@@ -46,7 +46,7 @@ class TestGenerate(unittest.TestCase):
             "hello",
             max_tokens=5,
             verbose=False,
-            logits_processor=logits_processor,
+            logits_processor=[logits_processor],
         )
         self.assertEqual(len(all_toks), len(init_toks) + 5)