community, core[callbacks]: move FileCallbackHandler from community to core (#20495)

**Description:** Move `FileCallbackHandler` from community to core
**Issue:** #20493 
**Dependencies:** None

(imo) `FileCallbackHandler` is a built-in LangChain callback handler
like `StdOutCallbackHandler` and should properly be in in core.

libs/core/langchain_core/callbacks/__init__.py

@@ -18,6 +18,7 @@ from langchain_core.callbacks.base import (
     RunManagerMixin,
     ToolManagerMixin,
 )
+from langchain_core.callbacks.file import FileCallbackHandler
 from langchain_core.callbacks.manager import (
     AsyncCallbackManager,
     AsyncCallbackManagerForChainGroup,
@@ -70,4 +71,5 @@ __all__ = [
     "AsyncCallbackManagerForChainGroup",
     "StdOutCallbackHandler",
     "StreamingStdOutCallbackHandler",
+    "FileCallbackHandler",
 ]

libs/core/langchain_core/callbacks/file.py

@@ -0,0 +1,72 @@
+"""Callback Handler that writes to a file."""
+
+from __future__ import annotations
+
+from typing import Any, Dict, Optional, TextIO, cast
+
+from langchain_core.agents import AgentAction, AgentFinish
+from langchain_core.callbacks import BaseCallbackHandler
+from langchain_core.utils.input import print_text
+
+
+class FileCallbackHandler(BaseCallbackHandler):
+    """Callback Handler that writes to a file."""
+
+    def __init__(
+        self, filename: str, mode: str = "a", color: Optional[str] = None
+    ) -> None:
+        """Initialize callback handler."""
+        self.file = cast(TextIO, open(filename, mode, encoding="utf-8"))
+        self.color = color
+
+    def __del__(self) -> None:
+        """Destructor to cleanup when done."""
+        self.file.close()
+
+    def on_chain_start(
+        self, serialized: Dict[str, Any], inputs: Dict[str, Any], **kwargs: Any
+    ) -> None:
+        """Print out that we are entering a chain."""
+        class_name = serialized.get("name", serialized.get("id", ["<unknown>"])[-1])
+        print_text(
+            f"\n\n\033[1m> Entering new {class_name} chain...\033[0m",
+            end="\n",
+            file=self.file,
+        )
+
+    def on_chain_end(self, outputs: Dict[str, Any], **kwargs: Any) -> None:
+        """Print out that we finished a chain."""
+        print_text("\n\033[1m> Finished chain.\033[0m", end="\n", file=self.file)
+
+    def on_agent_action(
+        self, action: AgentAction, color: Optional[str] = None, **kwargs: Any
+    ) -> Any:
+        """Run on agent action."""
+        print_text(action.log, color=color or self.color, file=self.file)
+
+    def on_tool_end(
+        self,
+        output: str,
+        color: Optional[str] = None,
+        observation_prefix: Optional[str] = None,
+        llm_prefix: Optional[str] = None,
+        **kwargs: Any,
+    ) -> None:
+        """If not the final action, print out observation."""
+        if observation_prefix is not None:
+            print_text(f"\n{observation_prefix}", file=self.file)
+        print_text(output, color=color or self.color, file=self.file)
+        if llm_prefix is not None:
+            print_text(f"\n{llm_prefix}", file=self.file)
+
+    def on_text(
+        self, text: str, color: Optional[str] = None, end: str = "", **kwargs: Any
+    ) -> None:
+        """Run when agent ends."""
+        print_text(text, color=color or self.color, end=end, file=self.file)
+
+    def on_agent_finish(
+        self, finish: AgentFinish, color: Optional[str] = None, **kwargs: Any
+    ) -> None:
+        """Run on agent end."""
+        print_text(finish.log, color=color or self.color, end="\n", file=self.file)

libs/core/tests/unit_tests/callbacks/test_imports.py

@@ -30,6 +30,7 @@ EXPECTED_ALL = [
     "AsyncCallbackManagerForChainGroup",
     "StdOutCallbackHandler",
     "StreamingStdOutCallbackHandler",
+    "FileCallbackHandler",
 ]
 
 

libs/langchain/langchain/callbacks/__init__.py

@@ -11,6 +11,7 @@ from typing import Any
 
 from langchain_core._api import LangChainDeprecationWarning
 from langchain_core.callbacks import (
+    FileCallbackHandler,
     StdOutCallbackHandler,
     StreamingStdOutCallbackHandler,
 )
@@ -21,7 +22,6 @@ from langchain_core.tracers.context import (
 )
 from langchain_core.tracers.langchain import LangChainTracer
 
-from langchain.callbacks.file import FileCallbackHandler
 from langchain.callbacks.streaming_aiter import AsyncIteratorCallbackHandler
 from langchain.callbacks.streaming_stdout_final_only import (
     FinalStreamingStdOutCallbackHandler,

libs/langchain/langchain/callbacks/file.py

@@ -1,69 +1,3 @@
-"""Callback Handler that writes to a file."""
+from langchain_core.callbacks.file import FileCallbackHandler
-from typing import Any, Dict, Optional, TextIO, cast
 
-from langchain_core.agents import AgentAction, AgentFinish
+__all__ = ["FileCallbackHandler"]
-from langchain_core.callbacks import BaseCallbackHandler
-from langchain_core.utils.input import print_text
-
-
-class FileCallbackHandler(BaseCallbackHandler):
-    """Callback Handler that writes to a file."""
-
-    def __init__(
-        self, filename: str, mode: str = "a", color: Optional[str] = None
-    ) -> None:
-        """Initialize callback handler."""
-        self.file = cast(TextIO, open(filename, mode, encoding="utf-8"))
-        self.color = color
-
-    def __del__(self) -> None:
-        """Destructor to cleanup when done."""
-        self.file.close()
-
-    def on_chain_start(
-        self, serialized: Dict[str, Any], inputs: Dict[str, Any], **kwargs: Any
-    ) -> None:
-        """Print out that we are entering a chain."""
-        class_name = serialized.get("name", serialized.get("id", ["<unknown>"])[-1])
-        print_text(
-            f"\n\n\033[1m> Entering new {class_name} chain...\033[0m",
-            end="\n",
-            file=self.file,
-        )
-
-    def on_chain_end(self, outputs: Dict[str, Any], **kwargs: Any) -> None:
-        """Print out that we finished a chain."""
-        print_text("\n\033[1m> Finished chain.\033[0m", end="\n", file=self.file)
-
-    def on_agent_action(
-        self, action: AgentAction, color: Optional[str] = None, **kwargs: Any
-    ) -> Any:
-        """Run on agent action."""
-        print_text(action.log, color=color or self.color, file=self.file)
-
-    def on_tool_end(
-        self,
-        output: str,
-        color: Optional[str] = None,
-        observation_prefix: Optional[str] = None,
-        llm_prefix: Optional[str] = None,
-        **kwargs: Any,
-    ) -> None:
-        """If not the final action, print out observation."""
-        if observation_prefix is not None:
-            print_text(f"\n{observation_prefix}", file=self.file)
-        print_text(output, color=color or self.color, file=self.file)
-        if llm_prefix is not None:
-            print_text(f"\n{llm_prefix}", file=self.file)
-
-    def on_text(
-        self, text: str, color: Optional[str] = None, end: str = "", **kwargs: Any
-    ) -> None:
-        """Run when agent ends."""
-        print_text(text, color=color or self.color, end=end, file=self.file)
-
-    def on_agent_finish(
-        self, finish: AgentFinish, color: Optional[str] = None, **kwargs: Any
-    ) -> None:
-        """Run on agent end."""
-        print_text(finish.log, color=color or self.color, end="\n", file=self.file)