On 2007-04-24, Thomas Nelson [EMAIL PROTECTED] wrote:
On Apr 23, 10:38 pm, Mel Wilson [EMAIL PROTECTED] wrote:
Even with a balanced tree, if a key in a node changes value,
you may have to re-balance the tree. Nothing in a Python list
says that a dictionary tree would have to be re-balanced if
Neil Cerutti wrote:
On 2007-04-24, Thomas Nelson [EMAIL PROTECTED] wrote:
On Apr 23, 10:38 pm, Mel Wilson [EMAIL PROTECTED] wrote:
Even with a balanced tree, if a key in a node changes value,
you may have to re-balance the tree. Nothing in a Python list
says that a dictionary tree would have
On 2007-04-25, Steve Holden [EMAIL PROTECTED] wrote:
Neil Cerutti wrote:
That would be documented as undefined behavior, and users
exhorted not to do such things.
Python's dictionaries are a proven winner--I'm definitely not an
advocate for changing them. But the general requirement for a
On Apr 23, 10:38 pm, Mel Wilson [EMAIL PROTECTED] wrote:
Neil Cerutti wrote:
The interpreter explains it: A list is not a hashable object.
Choosing a hash table instead of some kind of balanced tree seems
to be just an optimization. ;)
Even with a balanced tree, if a key in a node changes
On 2007-04-20, Gabriel Genellina [EMAIL PROTECTED] wrote:
En Fri, 20 Apr 2007 15:28:51 -0300, Bjoern Schliessmann
[EMAIL PROTECTED] escribió:
Luis M. González wrote:
I don't remember exactly where I read about it, but Guido said
once that tuples are being kept mainly for historical
On 2007-04-21, Steven D'Aprano [EMAIL PROTECTED] wrote:
On Fri, 20 Apr 2007 15:36:00 -0700, [EMAIL PROTECTED] wrote:
The article explains that, amongst other things, tuples are
faster than lists, so if you are working with constant values
(inmutables) they are more indicated than lists.
On 23 Apr 2007 17:19:15 +0200, Neil Cerutti [EMAIL PROTECTED] wrote:
So the question becomes: Why do Python dictionaries require keys
to be of an immutable type?
Dictionary keys are hashed values. If you change the key, you change
the hash and lose the pointer to the referenced object.
Or:
On 2007-04-23, Chris Cioffi [EMAIL PROTECTED] wrote:
On 23 Apr 2007 17:19:15 +0200, Neil Cerutti [EMAIL PROTECTED]
wrote:
So the question becomes: Why do Python dictionaries require
keys to be of an immutable type?
Dictionary keys are hashed values. If you change the key, you
change the
En Mon, 23 Apr 2007 12:46:13 -0300, Neil Cerutti [EMAIL PROTECTED]
escribió:
On 2007-04-23, Chris Cioffi [EMAIL PROTECTED] wrote:
On 23 Apr 2007 17:19:15 +0200, Neil Cerutti [EMAIL PROTECTED]
wrote:
So the question becomes: Why do Python dictionaries require
keys to be of an immutable
Neil Cerutti wrote:
On 2007-04-21, Steven D'Aprano [EMAIL PROTECTED] wrote:
On Fri, 20 Apr 2007 15:36:00 -0700, [EMAIL PROTECTED] wrote:
The article explains that, amongst other things, tuples are
faster than lists, so if you are working with constant values
(inmutables) they are more
On 2007-04-23, Steve Holden [EMAIL PROTECTED] wrote:
Neil Cerutti wrote:
So the question becomes: Why do Python dictionaries require
keys to be of an immutable type?
Because otherwise people would expect to be able to use a list
to select a dictionary entry even after they'd modified
Neil Cerutti wrote:
The interpreter explains it: A list is not a hashable object.
Choosing a hash table instead of some kind of balanced tree seems
to be just an optimization. ;)
Even with a balanced tree, if a key in a node changes value, you may
have to re-balance the tree. Nothing in a
[EMAIL PROTECTED] a écrit :
On Apr 20, 4:37 pm, John Machin [EMAIL PROTECTED] wrote:
One inessential but very useful thing about tuples when you have a lot
of them is that they are allocated the minimum possible amount of
memory. OTOH lists are created with some slack so that appending etc
can
[EMAIL PROTECTED] a écrit :
Please help me think of an example where immutable tuples are
essential.
Well, I don't know if they are essential - much of Python can be seen
as 'unessential' syntactic sugar (my, even the class statement is not
essential if you go that way).
It seems that
Please help me think of an example where immutable tuples are
essential.
It seems that everywhere a tuple is used one could just as easily use
a list instead.
chris
--
http://mail.python.org/mailman/listinfo/python-list
[EMAIL PROTECTED] wrote:
Please help me think of an example where immutable tuples are
essential.
When used as dictionary keys (also everywhere else where they must
be in a constant order).
Yes, this *is* used in practice.
Regards,
Björn
--
BOFH excuse #14:
sounds like a Windows
On Apr 20, 2:06 pm, [EMAIL PROTECTED]
[EMAIL PROTECTED] wrote:
Please help me think of an example where immutable tuples are
essential.
It seems that everywhere a tuple is used one could just as easily use
a list instead.
chris
I don't remember exactly where I read about it, but Guido
Luis M. González wrote:
I don't remember exactly where I read about it, but Guido said
once that tuples are being kept mainly for historical reasons.
Weren't tuples added when lists already existed?
Regards,
Björn
--
BOFH excuse #101:
Collapsed Backbone
--
Iou need only consider having cartesian coordinate sets as the keys
for an example. A 2 dimensional list might be overly expensive if your
coordinates span a large area but are relatively sparse.
--
http://mail.python.org/mailman/listinfo/python-list
En Fri, 20 Apr 2007 15:28:51 -0300, Bjoern Schliessmann
[EMAIL PROTECTED] escribió:
Luis M. González wrote:
I don't remember exactly where I read about it, but Guido said
once that tuples are being kept mainly for historical reasons.
Weren't tuples added when lists already existed?
Both
On Apr 20, 3:28 pm, Bjoern Schliessmann usenet-
[EMAIL PROTECTED] wrote:
Luis M. González wrote:
I don't remember exactly where I read about it, but Guido said
once that tuples are being kept mainly for historical reasons.
Weren't tuples added when lists already existed?
Regards,
Björn
On Apr 20, 6:09 pm, Bjoern Schliessmann usenet-
[EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] wrote:
Please help me think of an example where immutable tuples are
essential.
When used as dictionary keys (also everywhere else where they must
be in a constant order).
Yes, this *is* used in
The article explains that, amongst other things, tuples are faster
than lists, so if you are working with constant values (inmutables)
they are more indicated than lists.
Thanks. I thought Python's design wasn't so concerned with
optimizations.
Adding a new type just for optimization
On Apr 21, 7:09 am, Luis M. González [EMAIL PROTECTED] wrote:
On Apr 20, 3:28 pm, Bjoern Schliessmann usenet-
[EMAIL PROTECTED] wrote:
Luis M. González wrote:
I don't remember exactly where I read about it, but Guido said
once that tuples are being kept mainly for historical reasons.
On Apr 20, 4:37 pm, John Machin [EMAIL PROTECTED] wrote:
One inessential but very useful thing about tuples when you have a lot
of them is that they are allocated the minimum possible amount of
memory. OTOH lists are created with some slack so that appending etc
can avoid taking quadratic
[EMAIL PROTECTED] wrote:
On Apr 20, 4:37 pm, John Machin [EMAIL PROTECTED] wrote:
One inessential but very useful thing about tuples when you have a lot
of them is that they are allocated the minimum possible amount of
memory. OTOH lists are created with some slack so that appending etc
can
On Fri, 20 Apr 2007 15:53:45 -0700, garrickp wrote:
Speaking of inessential but very useful things, I'm also a big fan of
the tuple swap...
a = 2
b = 3
(a, b) = (b, a)
Since tuples are made by commas, not brackets, that can be written more
cleanly as:
a, b = b, a
The only exception is the
On Fri, 20 Apr 2007 15:36:00 -0700, [EMAIL PROTECTED] wrote:
The article explains that, amongst other things, tuples are faster
than lists, so if you are working with constant values (inmutables)
they are more indicated than lists.
Thanks. I thought Python's design wasn't so concerned
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