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Answer: B
Solution: x and y are sets.
What does the `-` do on sets?
It computes the "set difference".
The diagram makes it clear (credit in description):
The shaded region is the part of A which is not in B.
That is the set difference.
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ALT https://mathmonks.com/sets/set-operations#Difference
Answer: A
Solution: a and b are sets.
The code computes
a ^ b
What is this operator ^?
The operator's action is called Symmetric Difference.
The diagram shows it the symmetric difference of A and B as shaded:
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ALT Source: https://math.stackexchange.com/a/2948656
In Python there is a module called `decimal` which has you covered.
It is designed specially for exactly representing decimal numbers.
There you won't have such problems.
See image for demo. I hope this answer was helpful!
You can count backwards from the rightmost item.
The 2nd-last is at index -2,
the 3rd-last at -3, and so on.
See image:
Applying to this question
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`extend` and `append` are both list methods that seem similar
But don't confuse `extend` with `append`
`append` just adds the argument as one item to the list
`extend` unpacks the iterable and adds each item
See image for example:
