http://chriskief.com/2014/04/22/populate-and-validate-a-django-modelform-using-api-data-with-the-generic-createview/

view.py

from django.core.urlresolvers import reverse_lazy
from django.views.generic import CreateView
from app.forms import MyModelForm
from app.lib.api import API


class MyCreateView(CreateView):

    template_name = 'form.html'
    form_class = MyModelForm
    success_url = reverse_lazy('home')
    object = None

    # allow data to be passed to this
    # pulled from django/views/generic/edit.py/ModelFormMixin
    def get_form_kwargs(self, data=None):

        kwargs = super(MyCreateView, self).get_form_kwargs()

        # if we have data, set the form's data so that we can auto-submit this form (without POSTing)
        if data:
            kwargs.update({'initial': data, 'data': data})

        return kwargs

    def get(self, request, *args, **kwargs):

        # grab the data from the API
        data = API.get_data()

        formdata = {'user_id': data['user_id'],
                    'email': data['email'],
                    'first_name': data['first_name'],
                    'last_name': data['last_name']}

        form_class = self.get_form_class()
        # must instantiate the class directly and include the data object rather than use get_form
        # will set both the initial and instance data
        #form = self.get_form(form_class)
        form = form_class(**self.get_form_kwargs(formdata))

        # do we have a valid form submission
        if form.is_valid():
            return self.form_valid(form)
        else:
            return self.form_invalid(form)

    # once the user submits the form, validate the form and create the new user
    def post(self, request, *args, **kwargs):

        # setup the form
        # we can use get_form this time as we no longer need to set the data property
        form_class = self.get_form_class()
        form = self.get_form(form_class)

        # grab the data from the API
        data = API.get_data()

        form.initial = {'user_id': data['user_id'],
                        'email': data['email'],
                        'first_name': data['first_name'],
                        'last_name': data['last_name']}

        if form.is_valid():
            return self.form_valid(form)
        else:
            return self.form_invalid(form)