saving and loading objects from file using jsonpickle

Question

I have the following simple methods for writing a python object to a file using jsonpickle:

def json_serialize(obj, filename, use_jsonpickle=True):
    f = open(filename, 'w')
    if use_jsonpickle:
        import jsonpickle
        json_obj = jsonpickle.encode(obj)
        f.write(json_obj)
    else:
        simplejson.dump(obj, f) 
    f.close()

def json_load_file(filename, use_jsonpickle=True):
    f = open(filename)
    if use_jsonpickle:
        import jsonpickle
        json_str = f.read()
        obj = jsonpickle.decode(json_str)
    else:
        obj = simplejson.load(f)
    return obj

the problem is that whenever I use these, it loads my objects back as dictionaries (that have fields like: "py/object": "my_module.MyClassName") but not as an actual Python object of the type that was used to generate the json string. How can I make it so jsonpickle actually converts the loaded string back to the object?

to illustrate this with an example, consider the following:

class Foo:
    def __init__(self, hello):
    self.hello = hello

# make a Foo obj
obj = Foo("hello world")
obj_str = jsonpickle.encode(obj)
restored_obj = jsonpickle.decode(obj_str)
list_objects = [restored_obj]
# We now get a list with a dictionary, rather than
# a list containing a Foo object
print "list_objects: ", list_objects

This yields:

list_objects:  [{'py/object': 'as_events.Foo', 'hello': 'hello world'}]

Rather than something like: [Foo()]. How can I fix this?

thanks.

Answer 1

Make sure that use_jsonpickle == True in json_load_file(). It seems that you serialize using jsonpickle and load using json.

>>> import jsonpickle
>>> class A(object):
...    def __init__(self, name):
...       self.name = name
... 
>>> js = jsonpickle.encode(A('abc'))
>>> js
'{"py/object": "__main__.A", "name": "abc"}'     # <-- json string
>>> a = jsonpickle.decode(js)
>>> a
<__main__.A object at 0x7f826a87bd90>            # <-- python object
>>> a.name
u'abc'
>>> import json
>>> b = json.loads(js)
>>> b
{u'py/object': u'__main__.A', u'name': u'abc'}    # <-- dictionary

Make sure that object type is available

>>> del A
>>> c = jsonpickle.decode(js)                  # no type available
>>> c
{u'py/object': u'__main__.A', u'name': u'abc'}
>>> type(c)
<type 'dict'>
>>> class A(object):
...    def __init__(self, name):
...        self.name = name
... 
>>> d = jsonpickle.decode(js)                   # type is available
>>> d
<__main__.A object at 0x7f826a87bdd0>
>>> type(d)
<class '__main__.A'>

Answer 2

Hi all,

The correct answer was that I was not inheriting from "object". Without inheriting from object, jsonpickle cannot correctly decode classes that take one or more arguments in the constructor, it seems. I am by no means an expert but making it Foo(object) rather than Foo: in the class declaration fixed it.