langchain/prompts/example_selector/semantic_similarity.py/SemanticSimilarityExampleSelector/select_examples
class SemanticSimilarityExampleSelector:    def select_examples(self, input_variables: Dict[str, str]) -> List[dict]:
        """Select which examples to use based on semantic similarity."""
        # Get the docs with the highest similarity.
        if self.input_keys:
            input_variables = {key: input_variables[key] for key in self.input_keys}
        query = " ".join(sorted_values(input_variables))
        example_docs = self.vectorstore.similarity_search(query, k=self.k)
        # Get the examples from the metadata.
        # This assumes that examples are stored in metadata.
        examples = [dict(e.metadata) for e in example_docs]
        # If example keys are provided, filter examples to those keys.
        if self.example_keys:
            examples = [{k: eg[k] for k in self.example_keys} for eg in examples]
        return examples