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From: Sparky on 15 Jul 2010 15:37
Hello Python community!

I am building a JSON-RPC web application that uses quite a few models.
I would like to return JSON encoded object information and I need a
system to indicate which properties should be returned when the object
is translated to a JSON encoded string. Unfortunately, this
application runs on top of Google's App Engine and, thus, private
attributes are not an option. Also, a preliminary search leads me to
believe that there are no real established ways to annotate variables.
Ideally I want to do something like:

def to_JSON(self):
returnDict = {}
for member in filter(someMethod, inspect.getmembers(self)):
returnDict[member[0]] = member[1]
return json.dumps(returnDict)

I recognize that two solutions would be to 1) include a prefix like
"public_" before variable names or 2) have a list/tuple of attributes
that should be transmitted, simply using the "in" operator. However,
both these options seem like a pretty ungraceful way to do it. Does
anyone else have an idea? Are there any established methods to apply
metadata / annotations to variables in Python or do you believe one of
the above is a good "pythonic" way to solve this problem? I am using
2.6.

Thanks,
Sam
From: John Krukoff on 15 Jul 2010 16:26
On Thu, 2010-07-15 at 12:37 -0700, Sparky wrote:
<snip>
> the above is a good "pythonic" way to solve this problem? I am using
> 2.6.

Hopefully a helpful correction, but if you're running on google app
engine, you're using python 2.5 on the google side irrespective of what
you're running for development.

--
John Krukoff <jkrukoff(a)ltgc.com>
Land Title Guarantee Company

From: Sparky on 15 Jul 2010 18:30
On Jul 15, 2:26 pm, John Krukoff <jkruk...(a)ltgc.com> wrote:
> On Thu, 2010-07-15 at 12:37 -0700, Sparky wrote:
>
> <snip>
>
> > the above is a good "pythonic" way to solve this problem? I am using
> > 2.6.
>
> Hopefully a helpful correction, but if you're running on google app
> engine, you're using python 2.5 on the google side irrespective of what
> you're running for development.
>
> --
> John Krukoff <jkruk...(a)ltgc.com>
> Land Title Guarantee Company

Sorry about that and thanks for pointing out my mistake there.

Sam
From: Chris Rebert on 16 Jul 2010 05:22
On Thu, Jul 15, 2010 at 12:37 PM, Sparky <samnsparky(a)gmail.com> wrote:
> Hello Python community!
>
> I am building a JSON-RPC web application that uses quite a few models.
> I would like to return JSON encoded object information and I need a
> system to indicate which properties should be returned when the object
> is translated to a JSON encoded string. Unfortunately, this
> application runs on top of Google's App Engine and, thus, private
> attributes are not an option. Also, a preliminary search leads me to
> believe that there are no real established ways to annotate variables.
> Ideally I want to do something like:
>
> def to_JSON(self):
>        returnDict = {}
>        for member in filter(someMethod, inspect.getmembers(self)):
>                returnDict[member[0]] = member[1]
>        return json.dumps(returnDict)
>
> I recognize that two solutions would be to 1) include a prefix like
> "public_" before variable names or 2) have a list/tuple of attributes
> that should be transmitted, simply using the "in" operator. However,
> both these options seem like a pretty ungraceful way to do it. Does
> anyone else have an idea? Are there any established methods to apply
> metadata / annotations to variables in Python or do you believe one of
> the above is a good "pythonic" way to solve this problem?

Those are about as Pythonic as you're going to get; I for one find the
prefix (or similar) solution rather neat (Good luck pulling it off in
a less dynamic language!), but option (2) is probably better in your
particular case.
Remember that at class-definition-time, Python has no idea what
instance variables an object will have, so nothing exists for you to
annotate; hence we're left with solutions of the forms you've given.
You /could/ do something involving decorators and property()s, but
that would be more verbose, more unnecessarily complicated, and less
Pythonic.

Cheers,
Chris
--
http://blog.rebertia.com
From: Christian Heimes on 16 Jul 2010 05:57
> def to_JSON(self):
> returnDict = {}
> for member in filter(someMethod, inspect.getmembers(self)):
> returnDict[member[0]] = member[1]
> return json.dumps(returnDict)

By the way you don't need filter here. The getmembers() function has a
filter functions. It's called 'predicate'. Try inspect.getmembers(self,
someMethod).

http://docs.python.org/library/inspect.html#inspect.getmembers

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