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Nested classes are not serializable in python when trying JSON dump

I currently have two classes in Python like these ones

class person:
age=""
name=""
ranking =

def addRanking():
#Do Whatever treatment and add to the ranking dict

class ranking:
semester = ""
position = ""
gpa = ""


I have my list of person as a dictionary called dictP json.dumps() this dictionary but it seems that it doesn't work. Here is my function to dump to JSON

dictP

json.dumps()

def toJson():
jsonfile = open('dict.json', 'w')
print(json.dump(listP, jsonfile))


I get the famous: is not JSON serializable.

Would you know what I can do to help this problem. I thought that having two dictionaries (which are serializable) would avoid this kind of issue, but apparently not.

Thanks in advance

Edit:

Here is an example (typed on my phone sorry for typos, I'm not sure it does run but it's so you get the idea):

class person:
age=""
name=""
ranking =

def __init__(self, age, name):
self.age = age
self.name = name
self.ranking =

def addRanking(self,semester,position,gpa):
#if the semester is not already present in the data for that person
self.ranking[semester] = make_ranking(semester,position,gpa)

class ranking:
semester = ""
position = ""
gpa = ""

def __init__(self, semester, position, gpa):
self.semester = semester
self.position = position
self.gpa = gpa

dictP =


def make_person(age, name):
# Some stuff happens there
return person(age,name)

def make_ranking(semester,postion,gpa):
#some computation there
return ranking(semester,position,gpa)

def pretending_to_read_csv():
age = 12
name = "Alice"
p = make_person(age, name)
dictP["1"] = p

age = 13
name = "Alice"
p = make_person(age, name)
dictP["2"] = p

#We read a csv for ranking that gives us an ID
semester = 1
position = 4
gpa = 3.2
id = 1

dictP["1"].addRanking(semester, position, gpa)

semester = 2
position = 4
gpa = 3.2
id = 1

dictP["1"].addRanking(semester, position, gpa)


2 Answers
2

For a dictionary to be serializable, note that all the keys & values in that dictionary must be serializable as well. You did not show us what listP contains, but I'm guessing it's something like this:

listP

>>> listP
[<__main__.person instance at 0x107b65290>, <__main__.person instance at 0x107b65368>]


Python instances are not serializable.

I think you want a list of dictionaries, which would look like this:

>>> listP
['ranking': , 'age': 10, 'name': 'fred', 'ranking': , 'age': 20, 'name': 'mary']


This would serialize as you expect:

>>> import json
>>> json.dumps(listP)
'["ranking": , "age": 10, "name": "fred", "ranking": , "age": 20, "name": "mary"]'


UPDATE

(Thanks for adding example code.)

>>> pretending_to_read_csv()
>>> dictP
'1': <__main__.person instance at 0x107b65368>, '2': <__main__.person instance at 0x107b863b0>


Recall that user-defined classes cannot be serialized automatically. It's possible to extend the JSONEncoder directly to handle these cases, but all you really need is a function that can turn your object into a dictionary comprised entirely of primitives.

JSONEncoder

def convert_ranking(ranking):
return
"semester": ranking.semester,
"position": ranking.position,
"gpa": ranking.gpa

def convert_person(person):
return
"age": person.age,
"name": person.name,
"ranking": semester: convert_ranking(ranking) for semester, ranking in person.ranking.iteritems()


One more dictionary comprehension to actually do the conversion and you're all set:

>>> new_dict = person_id: convert_person(person) for person_id, person in dictP.iteritems()
>>> from pprint import pprint
>>> pprint(new_dict)
'1': 'age': 12,
'name': 'Alice',
'ranking': 1: 'gpa': 3.2, 'position': 4, 'semester': 1,
2: 'gpa': 3.2, 'position': 4, 'semester': 2,
'2': 'age': 13, 'name': 'Alice', 'ranking':


Since no user-defined objects are stuffed in there, this will serialize as you hope:

>>> json.dumps(new_dict)
'"1": "ranking": "1": "position": 4, "semester": 1, "gpa": 3.2, "2": "position": 4, "semester": 2, "gpa": 3.2, "age": 12, "name": "Alice", "2": "ranking": , "age": 13, "name": "Alice"'


listP

person

You can try calling json.dump on the .__dict__ member of your instance. You say that you have a list of person instances so try doing something like this:

json.dump

.__dict__

listJSON =
for p in listP
#append the value of the dictionary containing data about your person instance to a list
listJSON.append(p.__dict__)
json.dump(listJSON, jsonfile)


If you are storing your person instances in a dictionary like so: dictP = 'person1': p1, 'person2': p2 this solution will loop through the keys and change their corresponding values to the __dict__ member of the instance:

dictP = 'person1': p1, 'person2': p2

__dict__

for key in dictP:
dictP[key] = dictP[key].__dict__
json.dump(dictP, jsonfile)


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