[Python-Dev] Python 3.x and bytes (original) (raw)

Ethan Furman ethan at stoneleaf.us
Fri May 20 02:40:26 CEST 2011

Nick Coghlan wrote:

On Thu, May 19, 2011 at 6:43 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

For point 2, I'm personally +0 on the idea of having 1-element bytes and bytearray objects delegate hashing and comparison operations to the corresponding integer object. We have the power to make the obvious code correct code, so let's do that. However, the implications of the additional key collisions in value based containers may need to be explored further.

Several folk have said that objects that compare equal must hash equal...

Why? It's an honest question. Here's what I have tried:

--> class Wierd(): ... def init(self, value): ... self.value = value ... def eq(self, other): ... return self.value == other ... def hash(self): ... return hash((self.value + 13) ** 3) ... --> one = Wierd(1) --> two = Wierd(2) --> three = Wierd(3) --> one <Wierd object at 0x00BFE710> --> one == 1 True --> one == 2 False --> two == 2 True --> three == 3 True --> d = dict() --> d[one] = '1' --> d[two] = '2' --> d[three] = '3' --> d {<Wierd object at 0x00BFE710>: '1', <Wierd object at 0x00BFE870>: '3', <Wierd object at 0x00BFE830>: '2'} --> d[1] = '1.0' --> d[2] = '2.0' --> d[3] = '3.0' --> d {<Wierd object at 0x00BFE870>: '3', 1: '1.0', 2: '2.0', 3: '3.0', <Wierd object at 0x00BFE830>: '2', <Wierd object at 0x00BFE710>: '1'} --> d[2] '2.0' --> d[two] '2'

This behavior matches what I was imagining for having b'a' == 97. They compare equal, yet remain distinct objects for all other purposes.

If anybody has a link to or an explanation why equal values must be equal hashes I'm all ears. My apologies in advance if this is an incredibly naive question.

Ethan

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