Client constructor with openai_api_key or not ( empty constructor)?

Short Course Q&A Building Systems with the ChatGPT API
1

In the second Chapter or Them LLM, the Chat format and tokens…when explaining the way to use LLM appears that the code should be from 1.0.0

client = openai.OpenAI()

def get_completion(prompt, model="gpt-3.5-turbo"):
    messages = [{"role": "user", "content": prompt}]
    response = client.chat.completions.create(
        model=model,
        messages=messages,
        temperature=0
    )
    return response.choices[0].message.content

But when i translate/migrate using: Apply a GritQL pattern

from openai import OpenAI

client = OpenAI(api_key=os.environ['OPENAI_API_KEY'])

So the chapter is wrong ? any differnce beween client = OpenAI(api_key=os.environ[‘OPENAI_API_KEY’]) and client = OpenAI() ??

Another thing how would be the code with async/await ?

Thanks