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Re: Dict when defining not returning multi value key error

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On 8/1/2014 11:39 AM, Marko Rauhamaa wrote:
> Chris Angelico <rosuav@gmail.com>:
>
>>> but hash(x) == hash(y) does NOT imply that x == y.
>>
>> Hello, pigeonhole principle :) If this were false - that is, if equal
>> hashes DID imply equal objects - it would be necessary to completely
>> encode an object's state in its hash, and hashes would be impossibly
>> large. This would, in fact, destroy their value completely.
>
> Well, modern computing assumes precisely:
>
>     hash(x) == hash(y) => x == y

Assuming that a false statement is true does not make it true, and can 
and has gotten 'computing' into trouble.

> That principle is at play with strong authentication (HTTPS et al),
> version control (git et al),

The principle for these applications is

stronghash(x) == stronghash(y) => x == y with probability 1 (or 
indistinguishable from 1).

For mercurial, with no treat model, a 160 bit hash is used. Internet 
applications need more bits and carefully vetted algorithms to hopefully 
make the actual principle true.

-- 
Terry Jan Reedy

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Re: Dict when defining not returning multi value key error Dan Stromberg <drsalists@gmail.com> - 2014-07-31 20:12 -0700
  Re: Dict when defining not returning multi value key error Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-01 04:04 +0000
    Re: Dict when defining not returning multi value key error Ben Finney <ben+python@benfinney.id.au> - 2014-08-01 14:17 +1000
      Re: Dict when defining not returning multi value key error Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-01 13:31 +0000
        Re: Dict when defining not returning multi value key error Chris Angelico <rosuav@gmail.com> - 2014-08-01 23:57 +1000
          Re: Dict when defining not returning multi value key error Marko Rauhamaa <marko@pacujo.net> - 2014-08-01 18:39 +0300
            Re: Dict when defining not returning multi value key error Terry Reedy <tjreedy@udel.edu> - 2014-08-01 17:42 -0400
            Re: Dict when defining not returning multi value key error Chris Angelico <rosuav@gmail.com> - 2014-08-02 09:57 +1000
              Re: Dict when defining not returning multi value key error Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 09:41 +0300
                Re: Dict when defining not returning multi value key error Marko Rauhamaa <marko@pacujo.net> - 2014-08-02 10:06 +0300
                Re: Dict when defining not returning multi value key error Chris Angelico <rosuav@gmail.com> - 2014-08-02 20:58 +1000
            Re: Dict when defining not returning multi value key error Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-02 11:47 +1000
              Re: Dict when defining not returning multi value key error Chris Angelico <rosuav@gmail.com> - 2014-08-02 12:13 +1000

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