[Python] How to access ChatGPT with openai key?

I am trying to access openai chatgpt using python using the following code:

import openai

KEY = ...
openai.api_key = KEY

client = openai.OpenAI()

response = client.responses.create(
model="gpt-4.1",
input="Write a one-sentence bedtime story about a unicorn."
)

print(response.output_text)


However I get the error

openai.OpenAIError: The api_key client option must be set either by passing api_key to the client or by setting the OPENAI_API_KEY environment variable


The OpenAI documentation is totally useless as it does not show how to use the key, and asking ChatGPT itself I seem to get an incorrect answer on how to do that.

So how can I fix this code?

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