Make compatible with langchain-core 0.1 by conditionally importing _StreamingCallbackHandler

libs/langgraph/langgraph/pregel/__init__.py

@@ -39,7 +39,11 @@ from langchain_core.runnables.utils import (
     ConfigurableFieldSpec,
     get_unique_config_specs,
 )
-from langchain_core.tracers._streaming import _StreamingCallbackHandler
+
+try:
+    from langchain_core.tracers._streaming import _StreamingCallbackHandler
+except ImportError:
+    _StreamingCallbackHandler = None
 from pydantic import BaseModel
 from typing_extensions import Self
 
@@ -2529,13 +2533,17 @@ class Pregel(PregelProtocol):
             run_id=config.get("run_id"),
         )
         # if running from astream_log() run each proc with streaming
-        do_stream = next(
-            (
-                cast(_StreamingCallbackHandler, h)
-                for h in run_manager.handlers
-                if isinstance(h, _StreamingCallbackHandler)
-            ),
-            None,
+        do_stream = (
+            next(
+                (
+                    cast(_StreamingCallbackHandler, h)  # type: ignore
+                    for h in run_manager.handlers
+                    if isinstance(h, _StreamingCallbackHandler)
+                ),
+                None,
+            )
+            if _StreamingCallbackHandler is not None
+            else False
         )
         try:
             # assign defaults