Thank you everyone for the assistance and for the very informative
discussion
Regards
SM
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Gabriel Genellina wrote:
> En Thu, 20 Sep 2007 08:46:29 -0300, Steven D'Aprano
>
>> Another way is to use this class:
>>
>> class HashableList(list):
>> def __hash__(self):
>> return hash(tuple(self))
>
> ...and that will stop working as soon as the list is mutated (which is
> exact
En Thu, 20 Sep 2007 08:46:29 -0300, Steven D'Aprano
<[EMAIL PROTECTED]> escribi�:
> Another way is to use this class:
>
> class HashableList(list):
> def __hash__(self):
> return hash(tuple(self))
...and that will stop working as soon as the list is mutated (which is
exactly what
"Chris Mellon" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
| On 9/20/07, Dustan <[EMAIL PROTECTED]> wrote:
| > On Sep 19, 10:58 pm, Bryan Olson <[EMAIL PROTECTED]> wrote:
| > > Bad news: Python 3000 has no immutable type for byte-strings.
| > > The new bytes type cannot serve for
On 9/20/07, OKB (not okblacke) <[EMAIL PROTECTED]> wrote:
> Steven D'Aprano wrote:
>
> > But of course you can't look up the dict by value, only by
> > identity. But that's what you wanted.
>
> Actually, if I understand the OP's examples right, he wants to look
> up only by value, not by id
On 9/20/07, Dustan <[EMAIL PROTECTED]> wrote:
> On Sep 19, 10:58 pm, Bryan Olson <[EMAIL PROTECTED]> wrote:
> > Bad news: Python 3000 has no immutable type for byte-strings.
> > The new bytes type cannot serve for dict keys or set members.
> > Many things one would want to hash are unhashable -- fo
Steven D'Aprano wrote:
> But of course you can't look up the dict by value, only by
> identity. But that's what you wanted.
Actually, if I understand the OP's examples right, he wants to look
up only by value, not by identity.
--
--OKB (not okblacke)
Brendan Barnwell
"Do not follow whe
On 2007-09-20, Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote:
>> In the new model, it should be the value at the time of
>> addition. That is [1,2] (not [1,2,3]). This does mean a copy
>> of key in maintained internally in the dict.
>
> A copy!? That has to be a deep copy. Which would make
>
> Steven D'Aprano <[EMAIL PROTECTED]> (SD) wrote:
>SD> In other words, if you have two mutable objects M1 and M2, then you
>SD> expect:
>SD> hash(M1) == hash(M2) if and only if M1 and M2 are equal
>SD> hash(M1) != hash(M2) if M1 and M2 are unequal
Huh? Unequal things may hash to the same va
On Thu, 20 Sep 2007 04:02:03 +, Karthik Gurusamy wrote:
> On Sep 19, 7:17 pm, Steven D'Aprano <[EMAIL PROTECTED]
> cybersource.com.au> wrote:
>> On Wed, 19 Sep 2007 20:58:03 +, Karthik Gurusamy wrote:
>> > While it's easy to explain the behavior, I think the decision to dis-
>> > allow mut
On Sep 19, 10:58 pm, Bryan Olson <[EMAIL PROTECTED]> wrote:
> Bad news: Python 3000 has no immutable type for byte-strings.
> The new bytes type cannot serve for dict keys or set members.
> Many things one would want to hash are unhashable -- for
> example, the results of the hash functions in hash
Karthik Gurusamy wrote:
> On Sep 19, 7:17 pm, Steven D'Aprano <[EMAIL PROTECTED]
> cybersource.com.au> wrote:
>> On Wed, 19 Sep 2007 20:58:03 +, Karthik Gurusamy wrote:
>>> While it's easy to explain the behavior, I think the decision to dis-
>>> allow mutable items as keys is a bit arbitrary.
On Sep 20, 9:50 am, thebjorn <[EMAIL PROTECTED]>
wrote:
it's bad form to reply to myself, I know, but
> def __iter__(self):
> for k in super(mdict,self).__iter__():
> yield eval(k)
should probably be
def __iter__(self):
return (eval(k) for k in super(mdict,se
On Sep 20, 6:02 am, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
> On Sep 19, 7:17 pm, Steven D'Aprano <[EMAIL PROTECTED]
>
[...]
> > (2) Allow the hash of mutable objects to change, which means you can use
> > mutable objects as keys in dicts but if you change them, you can no
> > longer find them
On Thu, 20 Sep 2007 03:46:08 +, prikar20 wrote:
> On Sep 19, 5:25 pm, Mark Dickinson <[EMAIL PROTECTED]> wrote:
>> On Sep 19, 7:26 pm, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
>>
>> > If I did, a = [10, 20] and I did d[a]= 'foo', then a.append(30).
>> > If dict complains key error on d[a] n
On Sep 20, 4:17 am, Steven D'Aprano <[EMAIL PROTECTED]
cybersource.com.au> wrote:
[...]
> Data structures don't have problems. Programmers do.
That's QOTW material :-)
> ... And language
> designers with sense build languages that minimize the programmers
> problems, not maximize them.
>
...
>
>
On Sep 20, 5:02 am, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
> In the new model, at the time of addition, you need to remember the
> key at that time. If it's a list, you make a copy of the items.
In other words you ask the dict to freeze any mutable keys given to
it.
Try an implementation and y
On Sep 19, 7:17 pm, Steven D'Aprano <[EMAIL PROTECTED]
cybersource.com.au> wrote:
> On Wed, 19 Sep 2007 20:58:03 +, Karthik Gurusamy wrote:
> > While it's easy to explain the behavior, I think the decision to dis-
> > allow mutable items as keys is a bit arbitrary. There is no need for
> > dict
Karthik Gurusamy wrote:
> While it's easy to explain the behavior, I think the decision to dis-
> allow mutable items as keys is a bit arbitrary.
Furthermore, it's not really true.
class Blurf (object):
def __init__(self, intval):
self.seti(intval)
def seti(se
On Sep 19, 5:25 pm, Mark Dickinson <[EMAIL PROTECTED]> wrote:
> On Sep 19, 7:26 pm, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
>
> > If I did, a = [10, 20] and I did d[a]= 'foo', then a.append(30).
> > If dict complains key error on d[a] now, I won't be surprised. If I do
> > d[[10, 20, 30]], I wi
On Wed, 19 Sep 2007 20:58:03 +, Karthik Gurusamy wrote:
> While it's easy to explain the behavior, I think the decision to dis-
> allow mutable items as keys is a bit arbitrary. There is no need for
> dict to recompute hash
What???
Of course it does. How else can it look up the key? Because
On Sep 19, 7:26 pm, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
> If I did, a = [10, 20] and I did d[a]= 'foo', then a.append(30).
> If dict complains key error on d[a] now, I won't be surprised. If I do
> d[[10, 20, 30]], I will be surprised if it doesn't find the item. Of
> course, in today's beh
On Sep 19, 3:06 pm, Paddy <[EMAIL PROTECTED]> wrote:
> On Sep 19, 9:58 pm, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
>
> > Since we know hashing is used, all that is needed is, a well-defined
> > way to construct a hash out of a mutable. "Given a sequence, how to
> > get a hash" is the problem. I
On Sep 19, 9:58 pm, Karthik Gurusamy <[EMAIL PROTECTED]> wrote:
>
> Since we know hashing is used, all that is needed is, a well-defined
> way to construct a hash out of a mutable. "Given a sequence, how to
> get a hash" is the problem. If later the given sequence is different,
> that's not the dic
On Sep 19, 6:16 am, Sion Arrowsmith <[EMAIL PROTECTED]>
wrote:
> sapsi <[EMAIL PROTECTED]> wrote:
> > Why can't lists be hashed?
>
> Several people have answered "because they're mutable" without
> explaining why mutability precludes hashing. So:
>
> Consider a dict (dicts have been in Python a *l
sapsi <[EMAIL PROTECTED]> wrote:
> Why can't lists be hashed?
Several people have answered "because they're mutable" without
explaining why mutability precludes hashing. So:
Consider a dict (dicts have been in Python a *lot* longer than
sets, and have the same restriction) which allowed lists as
On 9/19/07, Paddy <[EMAIL PROTECTED]> wrote:
> frozenset over turning the embedded list into a tuple?
> The tuple would preserve order in the item (1,2)
> a = set([1,2,3, (1,2)])
The OP was probably thinking in mathematical terms as in "the set of
all the possible subsets of the set composed b
On Sep 19, 1:59 am, Raymond Hettinger <[EMAIL PROTECTED]> wrote:
> On Sep 18, 5:39 pm, sapsi <[EMAIL PROTECTED]> wrote:
>
> > I recently tried using the set function in Python and was surprised to
> > find that
>
> > a=[ 1, 2,3, [1,2] ]
>
> > doesn't work with 'set', throwing TyperError (unhashable
On Sep 18, 7:39 pm, sapsi <[EMAIL PROTECTED]> wrote:
> Hello,
> I recently tried using the set function in Python and was surprised to
> find that
>
> a=[ 1, 2,3, [1,2] ]
>
> doesn't work with 'set', throwing TyperError (unhashable exception). I
> found out that this is because lists can't be hashe
On Sep 19, 10:39 am, sapsi <[EMAIL PROTECTED]> wrote:
> My question is,
> 1) Why can't lists be hashed?
They are mutable.
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http://mail.python.org/mailman/listinfo/python-list
On Sep 18, 5:39 pm, sapsi <[EMAIL PROTECTED]> wrote:
> I recently tried using the set function in Python and was surprised to
> find that
>
> a=[ 1, 2,3, [1,2] ]
>
> doesn't work with 'set', throwing TyperError (unhashable exception). I
> found out that this is because lists can't be hashed.
> So,t
sapsi wrote:
> 2) This is not related, but is there i neat way (without pop and list
> comprehension) to convert a set into a list? I say neat because i'm
> guessing using list comprehension might turn out be slow and there
> might be other methods which are faster.
a = set([1, 2, 3, 4])
b = list(
Hello,
I recently tried using the set function in Python and was surprised to
find that
a=[ 1, 2,3, [1,2] ]
doesn't work with 'set', throwing TyperError (unhashable exception). I
found out that this is because lists can't be hashed.
So,this implies 'a' cannot be a set in python which i think is
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