How to use the pyquery.pyquery.no_default function in pyquery

def test_get_root(self):
        doc = pq(b'<p>')
        self.assertEqual(isinstance(doc.root, etree._ElementTree), True)
        self.assertEqual(doc.encoding, 'UTF-8')

        child = doc.children().eq(0)
        self.assertNotEqual(child._parent, no_default)
        self.assertTrue(isinstance(child.root, etree._ElementTree))
</p>

# -*- coding: utf-8 -*-
from .pyquery import PyQuery as Base
from .pyquery import no_default

from webob import Request
from webob import Response

try:
    from restkit.contrib.wsgi_proxy import HostProxy
except ImportError:
    HostProxy = no_default  # NOQA


class PyQuery(Base):

    def __init__(self, *args, **kwargs):
        if 'response' in kwargs:
            self.response = kwargs.pop('response')
        else:
            self.response = Response()
        if 'app' in kwargs:
            self.app = kwargs.pop('app')
            if len(args) == 0:
                args = [[]]
        else:
            self.app = no_default
        Base.__init__(self, *args, **kwargs)

def _wsgi_get(self, path_info, **kwargs):
        if path_info.startswith('/'):
            if 'app' in kwargs:
                app = kwargs.pop('app')
            elif self.app is not no_default:
                app = self.app
            else:
                raise ValueError('There is no app available')
        else:
            if HostProxy is not no_default:
                app = HostProxy(path_info)
                path_info = '/'
            else:
                raise ImportError('restkit is not installed')

        environ = kwargs.pop('environ').copy()
        environ.update(kwargs)

        # unsuported (came from Deliverance)
        for key in ['HTTP_ACCEPT_ENCODING', 'HTTP_IF_MATCH',
                    'HTTP_IF_UNMODIFIED_SINCE', 'HTTP_RANGE', 'HTTP_IF_RANGE']:

def __init__(self, *args, **kwargs):
        if 'response' in kwargs:
            self.response = kwargs.pop('response')
        else:
            self.response = Response()
        if 'app' in kwargs:
            self.app = kwargs.pop('app')
            if len(args) == 0:
                args = [[]]
        else:
            self.app = no_default
        Base.__init__(self, *args, **kwargs)
        if self._parent is not no_default:
            self.app = self._parent.app

def __init__(self, *args, **kwargs):
        if 'response' in kwargs:
            self.response = kwargs.pop('response')
        else:
            self.response = Response()
        if 'app' in kwargs:
            self.app = kwargs.pop('app')
            if len(args) == 0:
                args = [[]]
        else:
            self.app = no_default
        Base.__init__(self, *args, **kwargs)
        if self._parent is not no_default:
            self.app = self._parent.app