Python: convert class into json without None

MyEncoder.py

from json import JSONEncoder

class MyEncoder(JSONEncoder):
    def default(self, o):
        temp = o.__dict__
        a = dict()
        for k, v in temp.iteritems():
            if v is not None:
                if type(v) is list:
                    v = [x for x in v if x is not None]
                a[k] = v
        return a

class Person:
    def __init__(self, name, age=None):
        self.name = name
        self.age = age

sanghee = Person("sanghee", 35)
stranger1 = Person("stranger")
stranger2 = Person(["a", None, "b"])
stranger3 = Person(["a", None, "b"], 21)

print MyEncoder().encode(sanghee)
print MyEncoder().encode(stranger1)
print MyEncoder().encode(stranger2)
print MyEncoder().encode(stranger3)

Result

{"age": 35, "name": "sanghee"}
{"name": "stranger"}
{"name": ["a", "b"]}
{"age": 21, "name": ["a", "b"]}