fix: n_swapped check for generate (#73)

Author: jjmachan

src/ragas/metrics/llms.py

@@ -20,10 +20,12 @@ def generate(
     n: t.Optional[int] = None,
 ) -> LLMResult:
     old_n = None
+    n_swapped = False
     if n is not None:
         if isinstance(llm, OpenAI) or isinstance(llm, ChatOpenAI):
             old_n = llm.n
             llm.n = n
+            n_swapped = True
         else:
             raise Exception(
                 f"n={n} was passed to generate but the LLM {llm} does not support it."
@@ -36,6 +38,6 @@ def generate(
         ps = [p.format_messages() for p in prompts]
         result = llm.generate(ps)
 
-    if isinstance(llm, OpenAI) or isinstance(llm, ChatOpenAI):
+    if (isinstance(llm, OpenAI) or isinstance(llm, ChatOpenAI)) and n_swapped:
         llm.n = old_n  # type: ignore
     return result