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Why are there no ordered dictionaries?

This is probably a FAQ, but I dare to ask it nevertheless since I
haven't found a satisfying answer yet: Why isn't there an "ordered
dictionary" class at least in the standard list? Time and again I am
missing that feature. Maybe there is something wrong with my programming
style, but I rather think it is generally useful.

I fully agree with the following posting where somebody complains why so
very basic and useful things are not part of the standard library:
http://groups.google.com/group/comp....52d2f771a49857

Are there plans to get it into the standard lib sometime?

-- Christoph
Nov 22 '05 #1
210 10346
Christoph Zwerschke <ci**@online.de > wrote:
This is probably a FAQ, but I dare to ask it nevertheless since I
haven't found a satisfying answer yet: Why isn't there an "ordered
dictionary" class at least in the standard list?
What answers have you received that have not been satisfactory?

Some possible answers: The native dict is very fast, partly because
the implementation doesn't need to ensure any particular ordering.
Ordering the keys isn't the normal case, and can be done easily when
needed.

You asked "why not" rather than "has anyone done this anyway"; if
you asked the latter of the Python Cookbook, you might find something
like this:

<URL:http://aspn.activestat e.com/ASPN/Cookbook/Python/Recipe/107747>

A little old, and pre-dates subclassable native types, but quite
serviceable.
Time and again I am missing that feature. Maybe there is something
wrong with my programming style, but I rather think it is generally
useful.
In what cases do you find yourself needing a dict that preserves its
key order? Can you present a use case that would be improved by an
ordered dict?
I fully agree with the following posting where somebody complains
why so very basic and useful things are not part of the standard
library:
For my part, I consider it a virtue of Python that the standard
library doesn't change rapidly. It allows many competing
implementations to be shaken out before everyone starts depending on
any one of them.
Are there plans to get it into the standard lib sometime?


Where to find an answer:

<URL:http://www.python.org/peps/pep-0000.html>

Where to change that answer:

<URL:http://www.python.org/peps/pep-0001.html>

--
\ "One of the most important things you learn from the internet |
`\ is that there is no 'them' out there. It's just an awful lot of |
_o__) 'us'." -- Douglas Adams |
Ben Finney
Nov 22 '05 #2
Christoph Zwerschke <ci**@online.de > wrote:
This is probably a FAQ, but I dare to ask it nevertheless since I
haven't found a satisfying answer yet: Why isn't there an "ordered
dictionary" class at least in the standard list?
What answers have you received that have not been satisfactory?

Some possible answers: The native dict is very fast, partly because
the implementation doesn't need to ensure any particular ordering.
Ordering the keys isn't the normal case, and can be done easily when
needed.

You asked "why not" rather than "has anyone done this anyway"; if
you asked the latter of the Python Cookbook, you might find something
like this:

<URL:http://aspn.activestat e.com/ASPN/Cookbook/Python/Recipe/107747>

A little old, and pre-dates subclassable native types, but quite
serviceable.
Time and again I am missing that feature. Maybe there is something
wrong with my programming style, but I rather think it is generally
useful.
In what cases do you find yourself needing a dict that preserves its
key order? Can you present a use case that would be improved by an
ordered dict?
I fully agree with the following posting where somebody complains
why so very basic and useful things are not part of the standard
library:
For my part, I consider it a virtue of Python that the standard
library doesn't change rapidly. It allows many competing
implementations to be shaken out before everyone starts depending on
any one of them.
Are there plans to get it into the standard lib sometime?


Where to find an answer:

<URL:http://www.python.org/peps/pep-0000.html>

Where to change that answer:

<URL:http://www.python.org/peps/pep-0001.html>

--
\ "One of the most important things you learn from the internet |
`\ is that there is no 'them' out there. It's just an awful lot of |
_o__) 'us'." -- Douglas Adams |
Ben Finney
Nov 22 '05 #3

Uzytkownik "Christoph Zwerschke" <ci**@online.de > napisal w wiadomosci
news:dl******** **@online.de...
This is probably a FAQ, but I dare to ask it nevertheless since I
haven't found a satisfying answer yet: Why isn't there an "ordered
dictionary" class at least in the standard list? Time and again I am
missing that feature. Maybe there is something wrong with my programming
style, but I rather think it is generally useful.

I fully agree with the following posting where somebody complains why so
very basic and useful things are not part of the standard library:
http://groups.google.com/group/comp....52d2f771a49857

Are there plans to get it into the standard lib sometime?

-- Christoph


i am not sure what is the purpose of having ordered dictionaries built in
python, could u provide any examples?

i use a contruction:
for x in sorted(d.keys() )

cheers,

przemek
Nov 22 '05 #4

Uzytkownik "Christoph Zwerschke" <ci**@online.de > napisal w wiadomosci
news:dl******** **@online.de...
This is probably a FAQ, but I dare to ask it nevertheless since I
haven't found a satisfying answer yet: Why isn't there an "ordered
dictionary" class at least in the standard list? Time and again I am
missing that feature. Maybe there is something wrong with my programming
style, but I rather think it is generally useful.

I fully agree with the following posting where somebody complains why so
very basic and useful things are not part of the standard library:
http://groups.google.com/group/comp....52d2f771a49857

Are there plans to get it into the standard lib sometime?

-- Christoph


i am not sure what is the purpose of having ordered dictionaries built in
python, could u provide any examples?

i use a contruction:
for x in sorted(d.keys() )

cheers,

przemek
Nov 22 '05 #5

przemek drochomirecki wrote:
i am not sure what is the purpose of having ordered dictionaries built in
python, could u provide any examples?

i use a contruction:
for x in sorted(d.keys() )

By ordered dict, one usually wants order that is arbitary which cannot
be derived from the content, say insertion order(most ordered dict I
saw use this order).

I am writing a web applications(si mple forms) which has a number of
fields. Each field naturally has a name and a number of
attributes(form atting etc.), like this :

d = {'a':{...}, 'b':{....}}

This dict would be passed to the Kid template system which would lay it
out into a HTML form. For quick and dirty forms, I don't want to code
each field individually in the HTML template but just from top to
bottom(or left to right for a table) with a for loop.

However, I still want to group certain fields together. This is my need
of an ordered dict. Or course, I can pass a list along with the dict
and loop over the list and retrieve value from the dict, but that would
mean another things to pass along. And given the constraint of Kid
where everything must be one-liner(expressio n, no block of code), it
makes thing a bit harder.

Nov 22 '05 #6

przemek drochomirecki wrote:
i am not sure what is the purpose of having ordered dictionaries built in
python, could u provide any examples?

i use a contruction:
for x in sorted(d.keys() )

By ordered dict, one usually wants order that is arbitary which cannot
be derived from the content, say insertion order(most ordered dict I
saw use this order).

I am writing a web applications(si mple forms) which has a number of
fields. Each field naturally has a name and a number of
attributes(form atting etc.), like this :

d = {'a':{...}, 'b':{....}}

This dict would be passed to the Kid template system which would lay it
out into a HTML form. For quick and dirty forms, I don't want to code
each field individually in the HTML template but just from top to
bottom(or left to right for a table) with a for loop.

However, I still want to group certain fields together. This is my need
of an ordered dict. Or course, I can pass a list along with the dict
and loop over the list and retrieve value from the dict, but that would
mean another things to pass along. And given the constraint of Kid
where everything must be one-liner(expressio n, no block of code), it
makes thing a bit harder.

Nov 22 '05 #7
bo****@gmail.co m wrote:
I am writing a web applications(si mple forms) which has a number of
fields. Each field naturally has a name and a number of
attributes(form atting etc.), like this :

d = {'a':{...}, 'b':{....}}

This dict would be passed to the Kid template system which would lay it
out into a HTML form. For quick and dirty forms, I don't want to code
each field individually in the HTML template but just from top to
bottom(or left to right for a table) with a for loop.

However, I still want to group certain fields together. This is my need
of an ordered dict.


huh? if you want a list, use a list.

d = [('a', {...}), ('b', {....})]

</F>

Nov 22 '05 #8
bo****@gmail.co m wrote:
I am writing a web applications(si mple forms) which has a number of
fields. Each field naturally has a name and a number of
attributes(form atting etc.), like this :

d = {'a':{...}, 'b':{....}}

This dict would be passed to the Kid template system which would lay it
out into a HTML form. For quick and dirty forms, I don't want to code
each field individually in the HTML template but just from top to
bottom(or left to right for a table) with a for loop.

However, I still want to group certain fields together. This is my need
of an ordered dict.


huh? if you want a list, use a list.

d = [('a', {...}), ('b', {....})]

</F>

Nov 22 '05 #9

Fredrik Lundh wrote:
bo****@gmail.co m wrote:
I am writing a web applications(si mple forms) which has a number of
fields. Each field naturally has a name and a number of
attributes(form atting etc.), like this :

d = {'a':{...}, 'b':{....}}

This dict would be passed to the Kid template system which would lay it
out into a HTML form. For quick and dirty forms, I don't want to code
each field individually in the HTML template but just from top to
bottom(or left to right for a table) with a for loop.

However, I still want to group certain fields together. This is my need
of an ordered dict.


huh? if you want a list, use a list.

d = [('a', {...}), ('b', {....})]

Didn't I say that for quick and dirty form(usually first draft), I want
a list ? But the same template, it would(may) be further enhanced by
graphic designers in which case, I need direct access to the field
names, thus the dict property.

In this way, I don't have to change the python code just because I
change the presentation in the template.

Nov 22 '05 #10

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