langchain/callbacks/openai_info.py/OpenAICallbackHandler/__repr__
class OpenAICallbackHandler:    def __repr__(self) -> str:
        return (
            f"Tokens Used: {self.total_tokens}\n"
            f"\tPrompt Tokens: {self.prompt_tokens}\n"
            f"\tCompletion Tokens: {self.completion_tokens}\n"
            f"Successful Requests: {self.successful_requests}\n"
            f"Total Cost (USD): ${self.total_cost}"
        )