default sampling param should be deepcopied (#1581)

python/sglang/lang/interpreter.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import contextvars
+import copy
 import multiprocessing
 import queue
 import threading
@@ -652,7 +653,19 @@ class StreamExecutor:
                 self._init_var_event(e)
 
     def _resolve_sampling_params(self, sampling_params):
-        clone = None
+        """
+        Construct sampling param based on default + override values
+
+        The default values of sampling are populated in `default_sampling_para` via sgl.function.run(...sampling_args)
+        , and `sampling_params` contains the override values from sgl.gen().
+
+        Here we use default_sampling_para as the base and override the values if they exist in `sampling_params`.
+        It also extends the stop tokens based on the chat template.
+        """
+
+        # deepcopy is required because the dict has lists inside
+        clone = copy.deepcopy(self.default_sampling_para)
+
         for item in [
             "max_new_tokens",
             "stop",
@@ -674,20 +687,16 @@ class StreamExecutor:
         ]:
             value = getattr(sampling_params, item, None)
             if value is not None:
-                if clone is None:
-                    clone = self.default_sampling_para.clone()
                 setattr(clone, item, value)
 
         if self.chat_template.stop_str:
-            if not clone:
-                clone = self.default_sampling_para.clone()
             if clone.stop == ():
                 clone.stop = []
             elif isinstance(clone.stop, str):
                 clone.stop = [clone.stop]
             clone.stop += self.chat_template.stop_str
 
-        return clone or self.default_sampling_para
+        return clone
 
     def __del__(self):
         self.end()

python/sglang/lang/ir.py

@@ -150,8 +150,8 @@ class SglFunction:
         self,
         *args,
         max_new_tokens: int = 128,
-        stop: Union[str, List[str]] = [],
-        stop_token_ids: Optional[List[int]] = [],
+        stop: Union[str, List[str]] = None,
+        stop_token_ids: Optional[List[int]] = None,
         temperature: float = 1.0,
         top_p: float = 1.0,
         top_k: int = -1,
@@ -169,6 +169,12 @@ class SglFunction:
     ):
         from sglang.lang.interpreter import run_program
 
+        # avoid using [] as the default arg: https://nikos7am.com/posts/mutable-default-arguments/
+        if stop is None:
+            stop = []
+        if stop_token_ids is None:
+            stop_token_ids = []
+
         default_sampling_para = SglSamplingParams(
             max_new_tokens=max_new_tokens,
             stop=stop,
@@ -193,8 +199,8 @@ class SglFunction:
         batch_kwargs,
         *,
         max_new_tokens: int = 128,
-        stop: Union[str, List[str]] = (),
-        stop_token_ids: Optional[List[int]] = [],
+        stop: Union[str, List[str]] = None,
+        stop_token_ids: Optional[List[int]] = None,
         temperature: float = 1.0,
         top_p: float = 1.0,
         top_k: int = -1,
@@ -212,6 +218,11 @@ class SglFunction:
     ):
         from sglang.lang.interpreter import run_program_batch
 
+        if stop is None:
+            stop = []
+        if stop_token_ids is None:
+            stop_token_ids = []
+
         assert isinstance(batch_kwargs, (list, tuple))
         if len(batch_kwargs) == 0:
             return []

python/sglang/srt/sampling/sampling_params.py

@@ -26,7 +26,7 @@ class SamplingParams:
         max_new_tokens: int = 128,
         min_new_tokens: int = 0,
         stop: Optional[Union[str, List[str]]] = None,
-        stop_token_ids: Optional[List[int]] = [],
+        stop_token_ids: Optional[List[int]] = None,
         temperature: float = 1.0,
         top_p: float = 1.0,
         top_k: int = -1,
@@ -41,6 +41,8 @@ class SamplingParams:
         n: int = 1,
         json_schema: Optional[str] = None,
     ) -> None:
+        if stop_token_ids is None:
+            stop_token_ids = []
         self.temperature = temperature
         self.top_p = top_p
         self.top_k = top_k

python/sglang/test/test_utils.py

@@ -85,7 +85,7 @@ def call_generate_vllm(prompt, temperature, max_tokens, stop=None, n=1, url=None
 
 
 def call_generate_outlines(
-    prompt, temperature, max_tokens, stop=[], regex=None, n=1, url=None
+    prompt, temperature, max_tokens, stop=None, regex=None, n=1, url=None
 ):
     assert url is not None