Adding timedelta support to JSONEncoder, and an example of how to add decode support to a serializer.

[radiosilence]

Whilst this commit adds encoding of timedeltas to a string of a floating
point value of the seconds, you must add your own serializer field for
whatever timedelta model field you are using. This is because Django doesn't
support any kind of timedelta field out-of-the-box, so you have to either
implement your own or use django-timedelta.

If this is the case and you want to serialise timedelta input, you will have
to implement your own special field to use for the timedelta, which is not
included in core as it is based on a 3rd party library. Here is an example:

import datetime
import timedelta
from django import forms
from django.core import validators
from django.core.exceptions import ValidationError
from django.utils.translation import ugettext_lazy as _
from rest_framework.fields import WritableField

class TimedeltaField(WritableField):
    type_name = 'TimedeltaField'
    form_field_class = forms.FloatField

    default_error_messages = {
        'invalid': _("'%s' value must be in seconds."),
    }

    def from_native(self, value):
        if value in validators.EMPTY_VALUES:
            return None

        try:
            return datetime.timedelta(seconds=float(value))
        except (TypeError, ValueError):
            msg = self.error_messages['invalid'] % value
            raise ValidationError(msg)

Which is based on the FloatField. This field can then be used in
your serializer like this:

from yourapp.fields import TimedeltaField

class YourSerializer(serializers.ModelSerializer):
    duration = TimedeltaField()

[lovelydinosaur]

Thx dude. Good point re. time delta fields.

[lovelydinosaur]

Reference for anyone coming across this searching for time delta support in REST framework...
As of this fix, you should now be able to use custom TimeDelta fields, as provided by eg. http://pypi.python.org/pypi/django-timedeltafield

[radiosilence]

It's weird, as timedelta seems like a primitive that Django should have a field for in core, really. Then we could have it in our core, too.

[lovelydinosaur]

Could try opening a ticket for it. They might go for it.

[lovelydinosaur]

https://code.djangoproject.com/ticket/2443

[jpadilla]

Django 1.8 has support for DurationField. This PR is partly related. Tracking support for Django 1.8's Duration field in #2481.