python simplejson decoding

[Arthur Mc Coy]

Hi Peter,


I implemented my decoder using your approach. Very positive.

But that is for simple objects. My objects have nested lists. For
example MyObject has property (member) called benchmarks, which is the
list of defined benchmarks. I'm not sure if obj.__dict__.update will
help me to copy nested information. I will see later. Now, when the
testing environment is ready, I go for real world application.


Thank you!

Kostia

On Mar 2, 4:24 pm, Peter Otten <__pete... at web.de> wrote:
> Arthur Mc Coy wrote:
> > Hi all,
>
> > I'm trying an example (in attached file, I mean the bottom of this
> > message).
>
> > First, I create a list of 3 objects. Then I do:
>
> > PutJSONObjects(objects)
> > objects = GetJSONObjects()
> > PutJSONObjects(objects, "objects2.json")
>
> > 1) PutJSONObjects(objects) method creates objects.json file (by
> > default). It works fine.
> > 2) Then objects = GetJSONObjects() method get the file contents and
> > return.
>
> > 3) Finally the script fails on the third method
> > PutJSONObjects(objects, "objects2.json")
> > saying: AttributeError: 'dict' object has no attribute '__dict__'
>
> > That is true, because objects returned by GetJSONObjects() is not a
> > list of objects, but simple string....
>
> > So here is the question, please, how should I DECODE .json file into
> > list of python objects so that I will be able to put the copy of these
> > objects into a new file called objects2.json ?
>
> > simplejson docs are hard to follow - without examples.
>
> I suggest that you use json instead which is part of the standard library
> since Python 2.6. The documentation is here:
>
> http://docs.python.org/library/json.html
>
> If you know that there are only MyObject instances you need a function to
> construct such a MyObject instance from a dictionary. You can then recreate
> the objects with
>
> objects = [object_from_dict(d) for d in json.load(f)]
>
> or, if all dictionaries correspond to MyObject instances
>
> objects = json.load(f, object_hook=object_from_dict)
>
> A general implementation for old-style objects (objects that don't derive
> from object) is a bit messy:
>
> # idea copied from pickle.py
> class Empty:
>     pass
>
> def object_from_dict(d):
>     obj = Empty()
>     obj.__class__ = MyObject
>     obj.__dict__.update((str(k), v) for k, v in d.iteritems()) # *
>     return obj
>
> If you are willing to make MyClass a newstyle class with
>
> class MyObject(object):
>     # ...
>
> the function can be simplified to
>
> def object_from_dict(d):
>     obj = object.__new__(MyObject)
>     obj.__dict__.update((str(k), v) for k, v in d.iteritems()) # *
>     return obj
>
> (*) I don't know if unicode attribute names can do any harm,
> obj.__dict__.update(d) might work as well.