Getting a dictionary from an object

Steven D'Aprano steve at REMOVETHIScyber.com.au
Sun Jul 24 16:02:03 CEST 2005


On Sun, 24 Jul 2005 12:07:02 +0300, Thanos Tsouanas wrote:

> On Sat, Jul 23, 2005 at 06:59:43PM -0600, Steven Bethard wrote:
>> Thanos Tsouanas wrote:
>> > 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?
>> 
>> Maybe I'm not understanding your problem, but have you looked at the 
>> builtin "vars()"?
> 
> 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.

You could have mentioned this earlier.

But I don't think you are correct. As far as I can see, properties do have
an entry in obj.__dict__ the same as other attributes, although there is
certainly some strangeness going on with properties.

Using the sample code from here:
http://www.python.org/2.2.3/descrintro.html#property

class C(object):
    def __init__(self):
        self.__x = 0
    def getx(self):
        return self.__x
    def setx(self, x):
        if x < 0: x = 0
        self.__x = x
    x = property(getx, setx)

I see _C__x in C().__dict__, exactly as expected. (The _C is Python's
standard name mangling of "semi-private" attributes starting with double
underscores.)

I can't see any way to inspect a Python object and get a list of
properties, so you might have to keep your own list: add a class-attribute
of your object which keeps a list of all the properties:

class Obj:
    # various methods, attributes and properties
    ...
    # keep a list of special properties that don't show 
    # up correctly in __dict__
    special = ['foo', 'bar']

    # now define a special method that makes a copy of 
    # __dict__ and adds special properties to it

    def objdict(self):
        D = self.__dict__.copy()
        # assume shallow copy is enough
        for property_name in self.special:
            D[property_name] = self.__getattribute__(property_name)
        return D

then call it when you need it:

print "My object has fields %(foo)s and %(bar)s." % obj.objdict()


It would be nice to see an easier way to introspect objects and get
a list of properties.


-- 
Steven.




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