Birdwatching in the park at the weekend, you note down every bird you see, in messy upper and lower case: "Robin" and "robin" are the same kind. Write kinds(birds) to return how many different kinds you saw. No birds means 0.
kinds(["Robin", "sparrow", "robin", "Crow"])→3kinds([])→0def kinds(birds):
unique = set()
# your code here: a set comprehension putting each name in lower case into unique
return len(unique)
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