How does Python3 compare floats when using `set`?

Asked Mar 14 '21 at 07:21

Active Mar 14 '21 at 08:20

Viewed 168 times

The set function in Python relies on the existence of a robust equality operator existing on the elements given to set.

Suppose we had a list of floating point numbers, xs, and we called set(xs). How will set compare the elements of xs? Will it check to see if two elements are within machine epsilon, or will it perform bitwise equality?

asked Mar 14 '21 at 07:21

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Equal to machine epsilon means bitwise equality. – Mad Physicist Mar 14 '21 at 07:24
Except stuff like nans – Mad Physicist Mar 14 '21 at 07:28
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hash-based containers use `__eq__` to compare equality, so it boils down to "how is equality implemented for `float` objects" – juanpa.arrivillaga Mar 14 '21 at 07:30
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Can you clarify what makes you think ``set`` would use *any* tolerance for checking ``float`` values? Are you aware how sets work, i.e. that they require consistent ``__hash__`` and ``__eq__`` of their elements? – MisterMiyagi Mar 14 '21 at 09:08
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As with most Python built-ins, you can define your own `set` subclass that does what you want. – martineau Mar 14 '21 at 09:43

How does Python3 compare floats when using `set`?

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