return {"score": score}evaluator = LengthComparisonPairwiseEvalutor()evaluator.evaluate_string_pairs(    prediction="The quick brown fox jumped over the lazy dog.",    prediction_b="The quick brown fox jumped over the dog.",)    {'score': 1}LLM-Based Exampleâ€‹That example was simple to illustrate the API, but it wasn't very useful in practice. Below, use an LLM with some custom instructions to form a simple preference scorer similar to the built-in PairwiseStringEvalChain. We will use ChatAnthropic for the evaluator chain.# %pip install anthropic# %env ANTHROPIC_API_KEY=YOUR_API_KEYfrom typing import Optional, Anyfrom langchain.evaluation import PairwiseStringEvaluatorfrom langchain.chat_models import ChatAnthropicfrom langchain.chains import LLMChainclass CustomPreferenceEvaluator(PairwiseStringEvaluator):    """    Custom evaluator to compare two strings using a custom LLMChain.    """    def __init__(self) -> None:        llm = ChatAnthropic(model="claude-2", temperature=0)        self.eval_chain = LLMChain.from_string(            llm,            """Which option is preferred? Do not take order into account. Evaluate based on accuracy and helpfulness. If neither is preferred, respond with C. Provide your reasoning, then finish with Preference: A/B/CInput: How do I get the path of the parent directory in python 3.8?Option A: You can use the following code:```pythonimport osos.path.dirname(os.path.dirname(os.path.abspath(__file__)))Option B: You can use the following code:from pathlib import