Getting a dictionary from an object

[Thanos Tsouanas]

Hello.

I would like to have a quick way to create dicts from object, so that a
call to foo['bar'] would return obj.bar.

The following works, but I would prefer to use a built-in way if one
exists. Is there one?

Thanks in advance.

class dictobj(dict):
"""
class dictobj(dict):
A dictionary d with an object attached to it,
which treats d['foo'] as d.obj.foo.
"""
def __init__(self, obj):
self.obj = obj
def __getitem__(sel f, key):
return self.obj.__geta ttribute__(key)

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Bruno Desthuilliers]

Re: Getting a dictionary from an object

Thanos Tsouanas a écrit :[color=blue]
> Hello.
>
> I would like to have a quick way to create dicts from object, so that a
> call to foo['bar'] would return obj.bar.
>
> The following works, but I would prefer to use a built-in way if one
> exists. Is there one?
>
> Thanks in advance.
>
> class dictobj(dict):
> """
> class dictobj(dict):
> A dictionary d with an object attached to it,
> which treats d['foo'] as d.obj.foo.
> """
> def __init__(self, obj):
> self.obj = obj
> def __getitem__(sel f, key):
> return self.obj.__geta ttribute__(key)[/color]

I'd replace this last line with:
return getattr(self.ob j, key)


Now given your specs, I don't see what's wrong with your solution.

[Thanos Tsouanas]

Re: Getting a dictionary from an object

On Sat, Jul 23, 2005 at 11:30:19AM +0200, Bruno Desthuilliers wrote:[color=blue]
> Thanos Tsouanas a écrit :[color=green]
> > class dictobj(dict):
> > """
> > class dictobj(dict):
> > A dictionary d with an object attached to it,
> > which treats d['foo'] as d.obj.foo.
> > """
> > def __init__(self, obj):
> > self.obj = obj
> > def __getitem__(sel f, key):
> > return self.obj.__geta ttribute__(key)[/color]
>
> I'd replace this last line with:
> return getattr(self.ob j, key)
>
> Now given your specs, I don't see what's wrong with your solution.[/color]

I just dont want to use my class, if one already exists in the
libraries (or any other way to achieve the same thing), that's all ;)

Thanks for the tip.

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Steven D'Aprano]

Re: Getting a dictionary from an object

On Sat, 23 Jul 2005 11:48:27 +0300, Thanos Tsouanas wrote:
[color=blue]
> Hello.
>
> I would like to have a quick way to create dicts from object, so that a
> call to foo['bar'] would return obj.bar.[/color]

That looks rather confusing to me. Why not just call obj.bar, since it
doesn't look like you are actually using the dictionary at all?
[color=blue]
> The following works, but I would prefer to use a built-in way if one
> exists. Is there one?
>
> Thanks in advance.
>
> class dictobj(dict):
> """
> class dictobj(dict):
> A dictionary d with an object attached to it,
> which treats d['foo'] as d.obj.foo.
> """
> def __init__(self, obj):
> self.obj = obj
> def __getitem__(sel f, key):
> return self.obj.__geta ttribute__(key)[/color]

I don't think this is particularly useful behaviour. How do you use it?

py> D = dictobj("hello world")
py> D
{}
py> D.obj
'hello world'
py> D["food"] = "spam"
py> D
{'food': 'spam'}
py> D["food"]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 5, in __getitem__
AttributeError: 'str' object has no attribute 'food'


--
Steven.

[Mike Meyer]

Re: Getting a dictionary from an object

Steven D'Aprano <steve@REMOVETH IScyber.com.au> writes:[color=blue]
> On Sat, 23 Jul 2005 11:48:27 +0300, Thanos Tsouanas wrote:[color=green]
>> Hello.
>>
>> I would like to have a quick way to create dicts from object, so that a
>> call to foo['bar'] would return obj.bar.[/color]
>
> That looks rather confusing to me. Why not just call obj.bar, since it
> doesn't look like you are actually using the dictionary at all?[/color]

Well, I needed exactly this functionality last week. I have a
collection of (rather messy) classes that have a slew of attributes as
values. I would have used a dictionary for this, but I didn't write
the code.

I have to be able to display these objects (in HTML, if it matters),
and have as a requirement that the format string live in a database.

My solution didn't look to different from dictobj. There's some extra
mechanism to fetch the format string from the database, and some
formatting of the attribute based on meta-information in the object,
but it's the same basic idea.
[color=blue][color=green]
>> class dictobj(dict):
>> """
>> class dictobj(dict):
>> A dictionary d with an object attached to it,
>> which treats d['foo'] as d.obj.foo.
>> """
>> def __init__(self, obj):
>> self.obj = obj
>> def __getitem__(sel f, key):
>> return self.obj.__geta ttribute__(key)[/color]
>
> I don't think this is particularly useful behaviour. How do you use it?[/color]

def __str__(self):
return self._format % self


<mike
--
Mike Meyer <mwm@mired.or g> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

[Thanos Tsouanas]

Re: Getting a dictionary from an object

On Sat, Jul 23, 2005 at 11:22:21PM +1000, Steven D'Aprano wrote:[color=blue]
> On Sat, 23 Jul 2005 11:48:27 +0300, Thanos Tsouanas wrote:[color=green]
> > Hello.
> >
> > I would like to have a quick way to create dicts from object, so that a
> > call to foo['bar'] would return obj.bar.[/color]
>
> That looks rather confusing to me. Why not just call obj.bar, since it
> doesn't look like you are actually using the dictionary at all?
>[color=green]
> > [...][/color]
>
> I don't think this is particularly useful behaviour. How do you use it?[/color]

print foo %do

where do is a dictobj object...

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Steven Bethard]

Re: Getting a dictionary from an object

Thanos Tsouanas wrote:[color=blue]
> I would like to have a quick way to create dicts from object, so that a
> call to foo['bar'] would return obj.bar.
>
> The following works, but I would prefer to use a built-in way if one
> exists. Is there one?[/color]

Maybe I'm not understanding your problem, but have you looked at the
builtin "vars()"?

STeVe

[Steven D'Aprano]

Re: Getting a dictionary from an object

On Sat, 23 Jul 2005 13:50:36 -0400, Mike Meyer wrote:
[color=blue][color=green]
>> I don't think this is particularly useful behaviour. How do you use it?[/color]
>
> def __str__(self):
> return self._format % self[/color]

That doesn't work. It calls self.__str__ recursively until Python halts
the process.
[color=blue][color=green][color=darkred]
>>> class Thing(dict):[/color][/color][/color]
.... _format = "Thing %s is good."
.... def __str__(self):
.... return self._format % self
....[color=blue][color=green][color=darkred]
>>> X = Thing()
>>> X # calls __repr__ so is safe[/color][/color][/color]
{}[color=blue][color=green][color=darkred]
>>> str(X) # not safe[/color][/color][/color]
File "<stdin>", line 4, in __str__
File "<stdin>", line 4, in __str__
...
File "<stdin>", line 4, in __str__
File "<stdin>", line 4, in __str__
RuntimeError: maximum recursion depth exceeded


--
Steven.

[Steven D'Aprano]

Re: Getting a dictionary from an object

On Sun, 24 Jul 2005 02:09:54 +0300, Thanos Tsouanas wrote:
[color=blue]
> On Sat, Jul 23, 2005 at 11:22:21PM +1000, Steven D'Aprano wrote:[color=green]
>> On Sat, 23 Jul 2005 11:48:27 +0300, Thanos Tsouanas wrote:[color=darkred]
>> > Hello.
>> >
>> > I would like to have a quick way to create dicts from object, so that a
>> > call to foo['bar'] would return obj.bar.[/color]
>>
>> That looks rather confusing to me. Why not just call obj.bar, since it
>> doesn't look like you are actually using the dictionary at all?
>>[color=darkred]
>> > [...][/color]
>>
>> I don't think this is particularly useful behaviour. How do you use it?[/color]
>
> print foo %do
>
> where do is a dictobj object...[/color]

Are you telling me that the ONLY thing you use dictobj objects for is to
print them?

I don't think so. I do know how to print an object, amazingly.

Perhaps you would like to explain how you use the rest of the
functionality of the dictobj, instead of taking my words out of context
and giving an inane answer.

Why jump through all those hoops to get attributes when Python already
provides indexing and attribute grabbing machinery that work well? Why do
you bother to subclass dict, only to mangle the dict __getitem__ method so
that you can no longer retrieve items from the dict?


--
Steven.

[Thanos Tsouanas]

Re: Getting a dictionary from an object

On Sun, Jul 24, 2005 at 01:43:43PM +1000, Steven D'Aprano wrote:[color=blue]
> On Sun, 24 Jul 2005 02:09:54 +0300, Thanos Tsouanas wrote:[color=green]
> >
> > print foo %do
> >
> > where do is a dictobj object...[/color]
>
> Are you telling me that the ONLY thing you use dictobj objects for is to
> print them?[/color]

I'm sorry to disappoint you, but yes. When you have a long text
template to fill-out, with lots of %(foo)s, and all those foos are
attributes of an object, it really helps to have dictobj.
[color=blue]
> I don't think so. I do know how to print an object, amazingly.[/color]

Please, tell me, how would you print it in my case?
[color=blue]
> Perhaps you would like to explain how you use the rest of the
> functionality of the dictobj, instead of taking my words out of context
> and giving an inane answer.[/color]

I dont see _ANY_ other functionality in the dictobj class. Do you?
[color=blue]
> Why jump through all those hoops to get attributes when Python already
> provides indexing and attribute grabbing machinery that work well? Why do
> you bother to subclass dict, only to mangle the dict __getitem__ method so
> that you can no longer retrieve items from the dict?[/color]

Because *obviously* I don't know of these indexing and attribute
grabbing machineries you are talking about in my case. If you cared to
read my first post, all I asked was for the "normal", "built-in" way to
do it. Now, is there one, or not?

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Thanos Tsouanas]

Re: Getting a dictionary from an object

On Sat, Jul 23, 2005 at 06:59:43PM -0600, Steven Bethard wrote:[color=blue]
> Thanos Tsouanas wrote:[color=green]
> > I would like to have a quick way to create dicts from object, so that a
> > call to foo['bar'] would return obj.bar.
> >
> > The following works, but I would prefer to use a built-in way if one
> > exists. Is there one?[/color]
>
> Maybe I'm not understanding your problem, but have you looked at the
> builtin "vars()"?[/color]

I didn't know about it, but I knew about object.__dict__ which is, as I
see equivalent with vars(object). But it doesn't do the job for me,
since it fails to grab all obj.foo's, some of them being properties,
etc.

vars() is good to know though, Thanks!

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Bruno Desthuilliers]

Re: Getting a dictionary from an object

Thanos Tsouanas a écrit :[color=blue]
> On Sun, Jul 24, 2005 at 01:43:43PM +1000, Steven D'Aprano wrote:[/color]

(snip)[color=blue]
>[color=green]
>>Why jump through all those hoops to get attributes when Python already
>>provides indexing and attribute grabbing machinery that work well? Why do
>>you bother to subclass dict, only to mangle the dict __getitem__ method so
>>that you can no longer retrieve items from the dict?[/color][/color]
[color=blue]
>
> Because *obviously* I don't know of these indexing and attribute
> grabbing machineries you are talking about in my case. If you cared to
> read my first post, all I asked was for the "normal", "built-in" way to
> do it. Now, is there one, or not?[/color]

If you re-read your first post, you'll notice that you didn't say
anything about the intention, only about implementation !-)

Now if your *only* need is to access object as a dict for formated
output, you don't need to subclass dict. This is (well, should be) enough:

class Wrapper(object) :
def __init__(self, obj):
self._obj = obj
def __getitem__(sel f, name):
return getattr(self._o bj, name)

This works with 'normal' attributes as well as with properties. Notice
that this wrapper is read-only, and don't pretend to be a real
dictionnary - but still it implements the minimum required interface for
"%(attname) s" like formatting.

HTH
Bruno

[Thanos Tsouanas]

Re: Getting a dictionary from an object

On Sun, Jul 24, 2005 at 02:01:30PM +0200, Bruno Desthuilliers wrote:[color=blue]
> Thanos Tsouanas a écrit :[color=green]
> > On Sun, Jul 24, 2005 at 01:43:43PM +1000, Steven D'Aprano wrote:
> >
> > Because *obviously* I don't know of these indexing and attribute
> > grabbing machineries you are talking about in my case. If you cared to
> > read my first post, all I asked was for the "normal", "built-in" way to
> > do it. Now, is there one, or not?[/color]
>
> If you re-read your first post, you'll notice that you didn't say
> anything about the intention, only about implementation !-)[/color]

"""The following works, but I would prefer to use a built-in way if one
exists. Is there one?"""
[color=blue]
> Now if your *only* need is to access object as a dict for formated
> output, you don't need to subclass dict. This is (well, should be) enough:
>
> class Wrapper(object) :
> def __init__(self, obj):
> self._obj = obj
> def __getitem__(sel f, name):
> return getattr(self._o bj, name)
>
> This works with 'normal' attributes as well as with properties. Notice
> that this wrapper is read-only, and don't pretend to be a real
> dictionnary - but still it implements the minimum required interface for
> "%(attname) s" like formatting.[/color]

Thanks!! You made clear what 'the extra functionality' was. Indeed
there is no need to subclass dict...
[color=blue]
> HTH[/color]

it does!
[color=blue]
> Bruno
> --
> http://mail.python.org/mailman/listinfo/python-list[/color]

--
Thanos Tsouanas .: My Music: http://www.thanostsouanas.com/
http://thanos.sians.org/ .: Sians Music: http://www.sians.org/

[Bruno Desthuilliers]

Re: Getting a dictionary from an object

Bruno Desthuilliers a écrit :
(snip)[color=blue]
> class Wrapper(object) :
> def __init__(self, obj):
> self._obj = obj
> def __getitem__(sel f, name):
> return getattr(self._o bj, name)[/color]

If you want the Wrapper to be more like a Decorator (ie still can use
the Wrapper object as if it was the wrapped object), you can add this:

def __getattr__(sel f, name):
return getattr(self._o bj, name)

def __setattr__(sel f, name, val):
if name == '_obj':
super(Wrapper, self).__setattr __(name, val)
else:
setattr(self._o bj, name, val)

The Python cookbook may have some receipes too for this kind of funny
things...

[Bruno Desthuilliers]

Re: Getting a dictionary from an object

Steven D'Aprano a écrit :[color=blue]
> On Sun, 24 Jul 2005 02:09:54 +0300, Thanos Tsouanas wrote:
>
>[/color]
(snip)[color=blue]
>
> Are you telling me that the ONLY thing you use dictobj objects for is to
> print them?
>
> I don't think so. I do know how to print an object, amazingly.
>
> Perhaps you would like to explain how you use the rest of the
> functionality of the dictobj, instead of taking my words out of context
> and giving an inane answer.
>
> Why jump through all those hoops to get attributes when Python already
> provides indexing and attribute grabbing machinery that work well? Why do
> you bother to subclass dict, only to mangle the dict __getitem__ method so
> that you can no longer retrieve items from the dict?
>[/color]

The idea of the OP is not to use the dictobj as a full fledged dict,
just to wrap the obj in something that is dict-like enough to be used
for "%(attname) s" formatting. I also assume that he doesn't want to
manually alter the code of each and every class to achieve this !-)

So we can certainly agree that subclassing dict here is overkill and a
bit misleading, but there are probably better ways to express this
feeling. Of course, it would have been simpler if the OP had tell us
from the start what was it's use case, but what...

One could of course use metaclass tricks and the like to customize the
objects __str__ or __repr__ (as in David Mertz's gnosis.magic package),
but that would be overkill too IMHO.

The plain old Decorator[1] pattern is probably enough in this case,
since it's quite easy to implement a generic Decorator in Python.
Another solution could be to dynamically modify the to-be-wrapped
object's class to add a __getitem__ method.