fix: fix ipython running error for Engine due to outlines nest_asyncio (#4582)

Co-authored-by: shuaills <shishuaiuoe@gmail.com>

python/sglang/utils.py

@@ -22,6 +22,7 @@ from typing import Any, Callable, List, Optional, Tuple, Type, Union
 import numpy as np
 import requests
 from IPython.display import HTML, display
+from pydantic import BaseModel
 from tqdm import tqdm
 
 from sglang.srt.utils import kill_process_tree
@@ -29,6 +30,36 @@ from sglang.srt.utils import kill_process_tree
 logger = logging.getLogger(__name__)
 
 
+def convert_json_schema_to_str(json_schema: Union[dict, str, Type[BaseModel]]) -> str:
+    """Convert a JSON schema to a string.
+    Parameters
+    ----------
+    json_schema
+        The JSON schema.
+    Returns
+    -------
+    str
+        The JSON schema converted to a string.
+    Raises
+    ------
+    ValueError
+        If the schema is not a dictionary, a string or a Pydantic class.
+    """
+    if isinstance(json_schema, dict):
+        schema_str = json.dumps(json_schema)
+    elif isinstance(json_schema, str):
+        schema_str = json_schema
+    elif issubclass(json_schema, BaseModel):
+        schema_str = json.dumps(json_schema.model_json_schema())
+    else:
+        raise ValueError(
+            f"Cannot parse schema {json_schema}. The schema must be either "
+            + "a Pydantic class, a dictionary or a string that contains the JSON "
+            + "schema specification"
+        )
+    return schema_str
+
+
 def get_exception_traceback():
     etype, value, tb = sys.exc_info()
     err_str = "".join(traceback.format_exception(etype, value, tb))