Check for single prompt in __call__ method of the BaseLLM class (#4892)
# Ensuring that users pass a single prompt when calling a LLM
- This PR adds a check to the `__call__` method of the `BaseLLM` class
to ensure that it is called with a single prompt
- Raises a `ValueError` if users try to call a LLM with a list of prompt
and instructs them to use the `generate` method instead
## Why this could be useful
I stumbled across this by accident. I accidentally called the OpenAI LLM
with a list of prompts instead of a single string and still got a
result:
```
>>> from langchain.llms import OpenAI
>>> llm = OpenAI()
>>> llm(["Tell a joke"]*2)
"\n\nQ: Why don't scientists trust atoms?\nA: Because they make up everything!"
```
It might be better to catch such a scenario preventing unnecessary costs
and irritation for the user.
## Proposed behaviour
```
>>> from langchain.llms import OpenAI
>>> llm = OpenAI()
>>> llm(["Tell a joke"]*2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/marcus/Projects/langchain/langchain/llms/base.py", line 291, in __call__
raise ValueError(
ValueError: Argument `prompt` is expected to be a single string, not a list. If you want to run the LLM on multiple prompts, use `generate` instead.
```
langchain
2aa37540 - Check for single prompt in __call__ method of the BaseLLM class (#4892)
