Thuita Wachira Thuita Wachira - 6 months ago 60
Python Question

Python Marshmallow: schema.loads() returns error for nested schema

I have the following objects.

class Notification(object):
def __init__(self, **kwargs):
self.name = kwargs.get('name', '')
self.locale = kwargs.get('locale', '')
self.text = kwargs.get('text', '')

def __repr__(self):
return '<Notification(name={self.name!r})>'.format(self=self)


class NotificationThrottle(object):
def __init__(self, **kwargs):
self.notification = kwargs.get('notification', '')
self.time_span = kwargs.get('time_span', '')
self.maximum_count = kwargs.get('maximum_count', '')
self.current_count = kwargs.get('current_count', '')
self.throttle_set_date = kwargs.get('throttle_set_date', '')

def __repr__(self):
return '<NotificationThottle(name={self.type!r})>'.format(self=self)


...and the following accompanying marshmallow schemas

from marshmallow import Schema, fields, post_load

class NotificationSchema(Schema):
name = fields.Str()
locale = fields.Str()
text = fields.Str()

@post_load
def make_notification(self, data):
return Notification(**data)


class NotificationThrottleSchema(Schema):
notification = fields.Nested(NotificationSchema)
time_span = fields.Int()
maximum_count = fields.Int()
current_count = fields.Int()
throttle_set_date = fields.DateTime()

@post_load
def make_notification_throttle(self, data):
return NotificationThrottle(**data)


With the following data:

notification_data = {
'name': "new_message",
'locale': "sw_KE",
'text': "mimi ni mzee"
}
notification_throttle_data = {
"time_span": 3600,
"maximum_count": 10,
"current_count": 1,
"throttle_set_date": datetime.utcnow().isoformat()}


I get the error below when trying to load the NotificationThrottleSchema above.

In [1]: from datetime import datetime

In [2]: from .schemas.throttle_schemas import NotificationSchema, NotificationThrottleSchema

In [3]: notification_data = {
'name': "new_message",
'locale': "sw_KE",
'text': "mimi ni mzee"
}

In [4]: notification_throttle_data = {
"time_span": 3600,
"maximum_count": 10,
"current_count": 1,
"throttle_set_date": datetime.utcnow().isoformat()}

In [5]: schema = NotificationSchema()

In [6]: notif_schema = schema.load(notification_data)

In [7]: notif = notif_schema.data

In [8]: notif
Out[8]: <Notification(name=u'new_message')>

In [9]: notification_throttle_data.update({'notification':notif})

In [10]: notification_throttle_data
Out[10]:
{'current_count': 1,
'maximum_count': 10,
'notification': <Notification(name=u'new_message')>,
'throttle_set_date': '2016-04-25T08:19:06.492310',
'time_span': 3600}

In [11]: notif_throttle_schema = NotificationThrottleSchema()

In [12]: notif_throttle = notif_throttle_schema.load(notification_throttle_data)

In [13]: notif_throttle
Out[13]: UnmarshalResult(data={'current_count': 1, 'maximum_count': 10, 'throttle_set_date': datetime.datetime(2016, 4, 25, 8, 19, 6, 492310), 'time_span': 3600}, errors={'notification': {u'_schema': [u'Invalid input type.']}})

In [14]: notif_throttle.data
Out[14]:
{'current_count': 1,
'maximum_count': 10,
'throttle_set_date': datetime.datetime(2016, 4, 25, 8, 19, 6, 492310),
'time_span': 3600}

In [15]:


As you can see, the deserialisation to an object of type NotificationThrottle fails with the cryptic error above.
I'm convinced that this is a problem with marshmallow itself, unless I misunderstood the working of the post_load method (it presumably returns the defined object)

Is there something i'm doing wrong?

Answer

You seem to be updating the notification_throttle_data with a notification object as opposed to the serialised object. https://marshmallow.readthedocs.org/en/latest/quickstart.html#serializing-objects-dumping

What you want to do is:

    notif_data = schema.dump(notification_data)
    notification_throttle_data.update({'notification':notif_data.data})       
    notif_throttle = notif_throttle_schema.load(notification_throttle_data)

UnmarshalResult(data=<__main__.NotificationThrottle object at 0x10a3d5a90>, errors={})
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