fix(core): Enable save method for ChatPromptTemplate by removing NotImplementedError override

libs/core/langchain_core/prompts/chat.py

@@ -1300,13 +1300,6 @@ def _prompt_type(self) -> str:
         """Name of prompt type. Used for serialization."""
         return "chat"
 
-    def save(self, file_path: Union[Path, str]) -> None:
-        """Save prompt to file.
-
-        Args:
-            file_path: path to file.
-        """
-        raise NotImplementedError
 
     @override
     def pretty_repr(self, html: bool = False) -> str:

tests/unit_tests/prompts/test_chat_prompt_template_save.py

@@ -0,0 +1,38 @@
+"""Test ChatPromptTemplate save method."""
+
+import json
+import tempfile
+from pathlib import Path
+from langchain_core.prompts import ChatPromptTemplate
+
+
+def test_chat_prompt_template_save() -> None:
+    """Test that ChatPromptTemplate can be saved to a file."""
+    # Create a simple chat prompt template
+    prompt = ChatPromptTemplate.from_messages([
+        ("system", "You are a helpful assistant."),
+        ("user", "{input}")
+    ])
+
+    # Save to a temporary file
+    with tempfile.NamedTemporaryFile(suffix=".json", delete=False) as tmp_file:
+        temp_path = Path(tmp_file.name)
+
+    try:
+        # This should not raise NotImplementedError anymore
+        prompt.save(temp_path)
+
+        # Verify the file was created and contains valid JSON
+        assert temp_path.exists()
+
+        with open(temp_path, "r") as f:
+            data = json.load(f)
+
+        # Verify basic structure
+        assert "_type" in data
+        assert data["_type"] == "chat"
+
+    finally:
+        # Clean up
+        if temp_path.exists():
+            temp_path.unlink()