context_size = model_token_mapping.get(modelname, None)
        if context_size is None:
            raise ValueError(
                f"Unknown model: {modelname}. Please provide a valid OpenAI model name."
                "Known models are: " + ", ".join(model_token_mapping.keys())
            )
        return context_size
    @property
    def max_context_size(self) -> int:
        """Get max context size for this model."""
        return self.modelname_to_contextsize(self.model_name)
[docs]    def max_tokens_for_prompt(self, prompt: str) -> int:
        """Calculate the maximum number of tokens possible to generate for a prompt.
        Args:
            prompt: The prompt to pass into the model.
        Returns:
            The maximum number of tokens to generate for a prompt.
        Example:
            .. code-block:: python
                max_tokens = openai.max_token_for_prompt("Tell me a joke.")
        """
        num_tokens = self.get_num_tokens(prompt)
        return self.max_context_size - num_tokens
[docs]class OpenAI(BaseOpenAI):
    """OpenAI large language models.
    To use, you should have the ``openai`` python package installed, and the
    environment variable ``OPENAI_API_KEY`` set with your API key.
    Any parameters that are valid to be passed to the openai.create call can be passed
    in, even if not explicitly saved on this class.
    Example:
        .. code-block:: python
            from langchain.llms import OpenAI
            openai = OpenAI(model_name="text-davinci-003")
    """
    @property
    def _invocation_params(self) -> Dict[str, Any]:
        return {**{"model": self.model_name}, **super()._invocation_params}