core[minor]: Implement aformat for FewShotPromptWithTemplates (#20039)

libs/core/langchain_core/prompts/few_shot_with_templates.py

@@ -101,6 +101,14 @@ class FewShotPromptWithTemplates(StringPromptTemplate):
         else:
             raise ValueError
 
+    async def _aget_examples(self, **kwargs: Any) -> List[dict]:
+        if self.examples is not None:
+            return self.examples
+        elif self.example_selector is not None:
+            return await self.example_selector.aselect_examples(kwargs)
+        else:
+            raise ValueError
+
     def format(self, **kwargs: Any) -> str:
         """Format the prompt with the inputs.
 
@@ -149,6 +157,42 @@ class FewShotPromptWithTemplates(StringPromptTemplate):
         # Format the template with the input variables.
         return DEFAULT_FORMATTER_MAPPING[self.template_format](template, **kwargs)
 
+    async def aformat(self, **kwargs: Any) -> str:
+        kwargs = self._merge_partial_and_user_variables(**kwargs)
+        # Get the examples to use.
+        examples = await self._aget_examples(**kwargs)
+        # Format the examples.
+        example_strings = [
+            # We can use the sync method here as PromptTemplate doesn't block
+            self.example_prompt.format(**example)
+            for example in examples
+        ]
+        # Create the overall prefix.
+        if self.prefix is None:
+            prefix = ""
+        else:
+            prefix_kwargs = {
+                k: v for k, v in kwargs.items() if k in self.prefix.input_variables
+            }
+            for k in prefix_kwargs.keys():
+                kwargs.pop(k)
+            prefix = await self.prefix.aformat(**prefix_kwargs)
+
+        # Create the overall suffix
+        suffix_kwargs = {
+            k: v for k, v in kwargs.items() if k in self.suffix.input_variables
+        }
+        for k in suffix_kwargs.keys():
+            kwargs.pop(k)
+        suffix = await self.suffix.aformat(
+            **suffix_kwargs,
+        )
+
+        pieces = [prefix, *example_strings, suffix]
+        template = self.example_separator.join([piece for piece in pieces if piece])
+        # Format the template with the input variables.
+        return DEFAULT_FORMATTER_MAPPING[self.template_format](template, **kwargs)
+
     @property
     def _prompt_type(self) -> str:
         """Return the prompt type key."""