fix: temperature parameter in generate_text not ignored. (#887)

Addresses #886. 

Temperature parameter is not anymore overwritten by calling to
`self.get_temperature(n=n)`. Now it will only call that method if no
parameter was given.

---------

Co-authored-by: Ivan Herreros <[email protected]>

Author: HerrIvan

src/ragas/llms/base.py

@@ -70,7 +70,7 @@ async def agenerate_text(
         self,
         prompt: PromptValue,
         n: int = 1,
-        temperature: float = 1e-8,
+        temperature: t.Optional[float] = None,
         stop: t.Optional[t.List[str]] = None,
         callbacks: Callbacks = None,
     ) -> LLMResult:
@@ -80,11 +80,13 @@ async def generate(
         self,
         prompt: PromptValue,
         n: int = 1,
-        temperature: float = 1e-8,
+        temperature: t.Optional[float] = None,
         stop: t.Optional[t.List[str]] = None,
         callbacks: Callbacks = None,
         is_async: bool = True,
     ) -> LLMResult:
+        if temperature is None:
+            temperature = 1e-8
         """Generate text using the given event loop."""
         if is_async:
             agenerate_text_with_retry = add_async_retry(
@@ -131,11 +133,14 @@ def generate_text(
         self,
         prompt: PromptValue,
         n: int = 1,
-        temperature: float = 1e-8,
+        temperature: t.Optional[float] = None,
         stop: t.Optional[t.List[str]] = None,
         callbacks: Callbacks = None,
     ) -> LLMResult:
-        temperature = self.get_temperature(n=n)
+        # figure out the temperature to set
+        if temperature is None:
+            temperature = self.get_temperature(n=n)
+
         if is_multiple_completion_supported(self.langchain_llm):
             return self.langchain_llm.generate_prompt(
                 prompts=[prompt],
@@ -161,11 +166,12 @@ async def agenerate_text(
         self,
         prompt: PromptValue,
         n: int = 1,
-        temperature: float = 1e-8,
+        temperature: t.Optional[float] = None,
         stop: t.Optional[t.List[str]] = None,
         callbacks: Callbacks = None,
     ) -> LLMResult:
-        temperature = self.get_temperature(n=n)
+        if temperature is None:
+            temperature = self.get_temperature(n=n)
         if is_multiple_completion_supported(self.langchain_llm):
             return await self.langchain_llm.agenerate_prompt(
                 prompts=[prompt],