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while True:
yes_no = input("Yes or no?: ")
if yes_no.lower() in ["yes", "no", "y", "n"]:
break
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yes_or_no = input("yes or no")
if yes_or_no == "no":
print("you choose no")
elif yes_or_no == "yes":
print("you choose yes")
else:
print("that is not a answer. sorry...")