|  | Class definition attribute order | | |
| | | Andrew Lentvorski |  |
|  Posted: Fri Aug 01, 2008 9:23 pm Post subject: Class definition attribute order |  |
How do I determine the order of definition of class attributes?
For example, if I have a class
class Test(object):
y = 11
x = 22
How do I tell that y was defined before x?
Thanks,
-a |
| |
| | | Miles | |
| | Posted: Fri Aug 01, 2008 9:47 pm Post subject: Re: Class definition attribute order | |
On Fri, Aug 1, 2008 at 7:23 PM, Andrew Lentvorski <bsder@allcaps.org> wrote:
| Quote: | How do I determine the order of definition of class attributes?
For example, if I have a class
class Test(object):
y = 11
x = 22
How do I tell that y was defined before x?
|
You can't. The order that the locals are bound is not something
that's preserved.
There are frameworks that simulate this, but they actually just store
the order that the attributes are initialized:
class Test(FrameworkClass):
y = FrameworkObject(11)
x = FrameworkObject(22)
where FrameworkObject is assigned a number from an incrementing
counter on initialization, and FrameworkClass has a metaclass that
sorts those objects when the class is created.
-Miles |
| |
| | | Ben Finney | |
| | Posted: Sat Aug 02, 2008 12:33 am Post subject: Re: Class definition attribute order | |
Andrew Lentvorski <bsder@allcaps.org> writes:
| Quote: | How do I determine the order of definition of class attributes?
For example, if I have a class
class Test(object):
y = 11
x = 22
How do I tell that y was defined before x?
|
Like any namespace, attributes of an object are implemented as a
dictionary. Dictionaries have no guaranteed order to their items.
If you want to preserve order, do so with a type that preserves such
order:
class Test(object):
ordered_things = [
('y', 11),
('x', 22),
]
If that doesn't meet your needs, perhaps you could describe what
problem you're trying to solve and we can address it better.
--
\ “We spend the first twelve months of our children's lives |
`\ teaching them to walk and talk and the next twelve years |
_o__) telling them to sit down and shut up.” —Phyllis Diller |
Ben Finney |
| |
| | | Benjamin | |
| | Posted: Sat Aug 02, 2008 2:47 am Post subject: Re: Class definition attribute order | |
On Aug 1, 6:23pm, Andrew Lentvorski <bs...@allcaps.org> wrote:
| Quote: | How do I determine the order of definition of class attributes?
For example, if I have a class
class Test(object):
y = 11
x = 22
How do I tell that y was defined before x?
|
You wait until Python 3.0 where you can do this sort of thing with
metaclasses.
|
| |
| | | Gabriel Genellina | |
| | Posted: Tue Aug 05, 2008 12:38 am Post subject: Re: Class definition attribute order | |
En Fri, 01 Aug 2008 23:47:42 -0300, Benjamin <musiccomposition@gmail.com>
escribi:
| Quote: | On Aug 1, 6:23pm, Andrew Lentvorski <bs...@allcaps.org> wrote:
How do I determine the order of definition of class attributes?
For example, if I have a class
class Test(object):
y = 11
x = 22
How do I tell that y was defined before x?
You wait until Python 3.0 where you can do this sort of thing with
metaclasses.
|
So the namespace that the metaclass receives when the class is created,
will be some kind of ordered dictionary?
Metaclasses are available for a long time ago, but the definition order is
lost right at the start, when the class body is executed. Will this step
be improved in Python 3.0 then?
--
Gabriel Genellina |
| |
| | | Michele Simionato | |
| | Posted: Tue Aug 05, 2008 3:05 am Post subject: Re: Class definition attribute order | |
On Aug 5, 4:38am, "Gabriel Genellina":
| Quote: |
So the namespace that the metaclass receives when the class is created,
will be some kind of ordered dictionary?
Metaclasses are available for a long time ago, but the definition order is
lost right at the start, when the class body is executed. Will this step
be improved in Python 3.0 then?
|
Yep. See LINK
(I am working on an English translation these days,
but for the moment you can use Google Translator).
M. Simionato |
| |
| | | Terry Reedy | |
| | Posted: Tue Aug 05, 2008 3:47 am Post subject: Re: Class definition attribute order | |
Michele Simionato wrote:
| Quote: | On Aug 5, 4:38 am, "Gabriel Genellina":
So the namespace that the metaclass receives when the class is created,
will be some kind of ordered dictionary?
Metaclasses are available for a long time ago, but the definition order is
lost right at the start, when the class body is executed. Will this step
be improved in Python 3.0 then?
Yep. See LINK
(I am working on an English translation these days,
but for the moment you can use Google Translator).
|
Bfiefly, as I understood the discussion some months ago: In 2.x, the
class body is executed in a local namespace implemented as a normal dict
and *then* passed to the metaclass. In 3.0, the metaclass gets brief
control *before* execution so, among other possibilities, it can
substitute an (insertion) ordered dict for the local namespace. I will
leave the details to Michele's article and its eventual translation.
tjr |
| |
| | | Gabriel Genellina | |
| | Posted: Tue Aug 05, 2008 4:06 am Post subject: Re: Class definition attribute order | |
En Tue, 05 Aug 2008 00:05:58 -0300, Michele Simionato
<michele.simionato@gmail.com> escribi:
| Quote: | On Aug 5, 4:38am, "Gabriel Genellina":
So the namespace that the metaclass receives when the class is created,
will be some kind of ordered dictionary?
Metaclasses are available for a long time ago, but the definition order
is
lost right at the start, when the class body is executed. Will this
step
be improved in Python 3.0 then?
Yep. See LINK
(I am working on an English translation these days,
but for the moment you can use Google Translator).
|
Grazie, questo un modo per praticare il mio italiano!
--
Gabriel Genellina |
| |
| | | Michele Simionato | |
| | Posted: Tue Aug 05, 2008 5:53 am Post subject: Re: Class definition attribute order | |
On Aug 5, 7:47am, Terry Reedy <tjre...@udel.edu> wrote:
| Quote: |
Bfiefly, as I understood the discussion some months ago: In 2.x, the
class body is executed in a local namespace implemented as a normal dict
and *then* passed to the metaclass. In 3.0, the metaclass gets brief
control *before* execution so, among other possibilities, it can
substitute an (insertion) ordered dict for the local namespace. I will
leave the details to Michele's article and its eventual translation.
tjr
|
BTW, since I do not really follow python-dev, do you know
if some consensus was reached on the issue of adding an ordered dict
implementation to the standard library? |
| |
| | | Terry Reedy | |
| | Posted: Tue Aug 05, 2008 4:14 pm Post subject: Re: Class definition attribute order | |
Michele Simionato wrote:
| Quote: |
BTW, since I do not really follow python-dev, do you know
if some consensus was reached on the issue of adding an ordered dict
implementation to the standard library?
|
I thought there was to be one added to collections, where default_dict
lives, but I do not remember seeing it. The discussion was on the
PY-3000 list. You could review the archives, or possibly the issues
list (bugs.python.org) or just ask there. |
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