langchain.core : Use shallow copy for schema manipulation in JsonOutputParser.get_format_instructions (#17162)

- **Description :**  

Fix: Use shallow copy for schema manipulation in get_format_instructions

Prevents side effects on the original schema object by using a
dictionary comprehension for a safer and more controlled manipulation of
schema key-value pairs, enhancing code reliability.

  - **Issue:**  #17161 
  - **Dependencies:** None
  -  **Twitter handle:** None

libs/langchain/langchain/output_parsers/pydantic.py

@@ -29,7 +29,8 @@ class PydanticOutputParser(JsonOutputParser):
             raise OutputParserException(msg, llm_output=json_object)
 
     def get_format_instructions(self) -> str:
-        schema = self.pydantic_object.schema()
+        # Copy schema to avoid altering original Pydantic schema.
+        schema = {k: v for k, v in self.pydantic_object.schema().items()}
 
         # Remove extraneous fields.
         reduced_schema = schema

libs/langchain/langchain/output_parsers/yaml.py

@@ -43,7 +43,8 @@ class YamlOutputParser(BaseOutputParser[T]):
             raise OutputParserException(msg, llm_output=text) from e
 
     def get_format_instructions(self) -> str:
-        schema = self.pydantic_object.schema()
+        # Copy schema to avoid altering original Pydantic schema.
+        schema = {k: v for k, v in self.pydantic_object.schema().items()}
 
         # Remove extraneous fields.
         reduced_schema = schema