how to invoke callback handler in langchain? - Stack Overflow

from langchain_openai import ChatOpenAI
from langchain.callbacks.stdout import StdOutCallbackHandler
from langchain.globals import set_debug

if __name__ == "__main__":
    set_debug(True)
    std_handler = StdOutCallbackHandler()
    llm = ChatOpenAI(
        model="gpt-4o",
        temperature=0.7,
        verbose=True,
        callbacks=[std_handler]
    )

    direct_response = llm.invoke("how big is the earth? Answer ultra-concisely.")