On Tue, Dec 22, 2020 at 5:20 AM David Mertz <me...@gnosis.cx> wrote:
>
> On Mon, Dec 21, 2020 at 5:56 PM Paul Bryan <pbr...@anode.ca> wrote:
>>
>> I'm interested in knowing when (id(x), x) would be preferable over (type(x),
>> x).
>
>
> Something along these lines:
>
> >>> class Point:
> ... def __init__(self, x, y):
> ... self.x = x
> ... self.y = y
> ... def __eq__(self, other):
> ... return self.x == other.x and self.y == other.y
> ... def __hash__(self):
> ... return 0 # Could make something better
> ...
> ...
> >>> p1, p2, p3 = Point(1, 1), Point(2, 2), Point(1, 1)
> >>> p1 == p2
> False
> >>> p1 == p3
> True
> >>> {p1, p2, p3}
> {<__main__.Point object at 0x7f61f66a2d00>, <__main__.Point object at
> 0x7f61f66a2f10>}
>
If equality is based on self.x and self.y, the easiest way to do the
hash is the same way:
def __hash__(self):
return hash((self.x, self.y))
But the real question is: Why do points compare equal based on their
locations, if you need them to be independently stored in a set?
Logically, if they are equal, the set either contains that one thing
or it doesn't.
ChrisA
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