Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #39175

Re: Dictionaries with tuples or tuples of tuples

Show key headers only | View raw

On 02/18/2013 09:17 PM, Jon Reyes wrote:
> Thanks Dave and Mitya for  enlightening me about dictionaries. I'm still confused about this though:
 >
 > " so that if two
 > key objects are equal, they stay equal, and if they differ, they stay
 > different. "
 >
 > What does this mean? I won't be comparing key objects with one 
another. Also, when I had two keys with the same value the value of the 
other key disappeared so I assume in runtime if there are multiple keys 
of the same value only the last one will appear.

You won't be, but dict will.

Dict is by definition a mapping where a value is assigned to a unique
key. If you have two keys and two values, and then change one key to
be equal to the second key, that's not kosher, because which value it's
supposed to return when you try to get it by that key?

So in effect, key's hash value should not change. If key is immutable,
you can be certain that it's hash value will not change. If it's
mutable, you have to make sure not to change the key in a way that'd
make its hash value different than it was.

  -m

-- 
Lark's Tongue Guide to Python: http://lightbird.net/larks/

Graphic design is the paradise of individuality, eccentricity, heresy,
abnormality, hobbies and humors.  George Santayana

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 16:52 -0800
  Re: Dictionaries with tuples or tuples of tuples Mitya Sirenef <msirenef@lightbird.net> - 2013-02-18 20:11 -0500
    Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 17:19 -0800
    Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 17:19 -0800
  Re: Dictionaries with tuples or tuples of tuples Roy Smith <roy@panix.com> - 2013-02-18 20:17 -0500
    Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 17:20 -0800
  Re: Dictionaries with tuples or tuples of tuples Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-19 01:37 +0000
    Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 17:38 -0800
      Re: Dictionaries with tuples or tuples of tuples Dave Angel <davea@davea.name> - 2013-02-18 20:51 -0500
      Re: Dictionaries with tuples or tuples of tuples Mitya Sirenef <msirenef@lightbird.net> - 2013-02-18 20:56 -0500
      Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 18:17 -0800
        Re: Dictionaries with tuples or tuples of tuples Mitya Sirenef <msirenef@lightbird.net> - 2013-02-18 21:54 -0500
        Re: Dictionaries with tuples or tuples of tuples Dave Angel <davea@davea.name> - 2013-02-18 22:14 -0500
        Re: Dictionaries with tuples or tuples of tuples Mitya Sirenef <msirenef@lightbird.net> - 2013-02-18 22:56 -0500
      Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 18:17 -0800
      Re: Dictionaries with tuples or tuples of tuples Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-02-19 02:34 +0000
        Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 18:39 -0800
        Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 18:39 -0800
    Re: Dictionaries with tuples or tuples of tuples Jon Reyes <everystepsayes@gmail.com> - 2013-02-18 17:38 -0800

csiph-web