Medea 0.3.2

JSON Object Mapper / Encoder

Simple utilities to map JSON to and from Python Objects.

medea

medea is a singledispatch function for JSON encoding.

lists, tuples and sequences are converted to lists. Items and values of dicts are recursively dispatched. Other types should be registered with dispatch function.

medea.register(date, lambda obj: obj.strftime('%Y-%m-%d'))

dob = date(1974, 3, 1)
assert medea(dob) == '1974-03-01'

bob = {
    'name': 'Bob',
    'age': 38,
    'colors': ('blue', 'red'),
    'dob': dob}

assert medea(bob) == {
    'name': 'Bob',
    'age': 38,
    'colors': ['blue', 'red'],
    'dob': '1974-03-01'}

Custom objects can be registered with a mapper:

class Pet(object):
    pass


class Dog(Pet):
    def __init__(self, name):
        self.name = name
        self.kind = 'Dog'


class Cat(Pet):
    def __init__(self, name):
        self.name = name
        self.kind = 'Cat'


class PetPerson(Person):
    pass


medea.register(PetPerson, MedeaCamelMapper('first_name', 'last_name', 'pets'))
medea.register(Pet, MedeaCamelMapper('name', 'kind'))

anne = PetPerson('Anne', 'Frank')
fido = Dog('Fido')
spot = Dog('Spot')
garfield = Cat('Garfield')
anne.pets = [fido, spot, garfield]
assert medea(anne) == {
    'firstName': 'Anne',
    'lastName': 'Frank',
    'pets': [
        {'kind': 'Dog', 'name': 'Fido'},
        {'kind': 'Dog', 'name': 'Spot'},
        {'kind': 'Cat', 'name': 'Garfield'}]}

MedeaEncoder

MedeaEncoder is a JSONEncoder using the medea function.

MedeaMapper

Create a mapper using Python attribute names as arguments. Attributes that are not whitelisted will not be serialized:

class Person(object):
    def __init__(self, first_name, last_name,
                 address='', phone_number='', dob=''):
        self.first_name = first_name
        self.last_name = last_name
        self.address = address
        self.phone_number = phone_number
        self.dob = dob


bob = Person('Bob', 'Hope', '123 Main', '123', '1903-05-29')

mapper = MedeaMapper('first_name', 'last_name',
                     'address', 'phone_number', 'dob')

bob_json = {
    'first_name': 'Bob',
    'last_name': 'Hope',
    'address': '123 Main',
    'phone_number': '123',
    'dob': '1903-05-29'}

assert mapper.to_json(bob) == bob_json

Attribute names can be overridden using **kwargs.

bob = Person('Bob', 'Hope', '123 Main', '123', '1903-05-29')

mapper = MedeaMapper('address', 'dob',
                     first_name='firstName', last_name='lastName')

bob_json = {
    'firstName': 'Bob',
    'lastName': 'Hope',
    'address': '123 Main',
    'dob': '1903-05-29'}

assert mapper.to_json(bob) == bob_json

MedeaCamelMapper may be useful if JSON is camel cased.

bob = Person('Bob', 'Hope', '123 Main', '123', '1903-05-29')

mapper = MedeaCamelMapper('first_name', 'last_name',
                          'address', 'phone_number', 'dob')

bob_json = {
    'firstName': 'Bob',
    'lastName': 'Hope',
    'address': '123 Main',
    'phoneNumber': '123',
    'dob': '1903-05-29'}

assert mapper.to_json(bob) == bob_json

A mapper can also map attribues from JSON onto the object:

bob = Person('Bob', 'Hope', '123 Main', '123', '1903-05-29')

bob_json_full = {
    'firstName': 'Bob',
    'lastName': 'Hope',
    'address': '123 Main',
    'phoneNumber': '123',
    'DOB': '1903-05-29'}

fred_json = {
    'firstName': 'Fred',
    'lastName': 'Rodgers'}

mapper = MedeaCamelMapper('first_name', 'last_name')
mapper_full = MedeaCamelMapper('first_name', 'last_name',
                               'address', 'phone_number', dob='DOB')

assert mapper.to_json(bob) == bob_json
assert mapper_full.to_json(bob) == bob_json_full

# Override Bob's name from Fred
mapper.from_json(fred_json, bob)

# Mapper only serializes names
assert mapper.to_json(bob) == fred_json
assert mapper_full.to_json(bob) != bob_json_full
assert bob.first_name == 'Fred'
assert bob.last_name == 'Rodgers'
assert bob.address == '123 Main'
assert bob.phone_number == '123'
assert bob.dob == '1903-05-29'

# Revert back to Bob's name
mapper.from_json(bob_json, bob)
assert mapper.to_json(bob) == bob_json
assert mapper_full.to_json(bob) == bob_json_full