Can't create GEnum in Python

I might be wrong, but it looks like all GEnum stuff was created to provide enums from C. But I would like to use GEnums from Python, for the following reasons:

1. To use custom GEnums in custom widget's properties (and being able to change them in GtkInspektor)
2. To set these properties from GSettings (through dconf-editor, for example)

Thus I was expecting the following code would work:

import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk, GObject

class SwitchToggleMode(GObject.GEnum):
    AUTO = 1
    ENABLED = 2
    DISABLED = 3

class SwitchBox(Gtk.Box):
    __gtype_name__ = "SwitchBox"

    def __init__(self):
        Gtk.Box.__init__(self)
        self.switch_inverse_mode = SwitchToggleMode.AUTO

    @GObject.Property(type=SwitchToggleMode, default=SwitchToggleMode.AUTO)
    def show_switch_inverse_mode(self):
        return self.switch_inverse_mode

    @show_switch_inverse_mode.setter
    def show_switch_inverse_mode(self, mode):
        self.switch_inverse_mode = mode

But I get TypeError: could not get typecode from object:

Traceback (most recent call last):
  File "/home/likern/Projects/PythonGUIGnome/test/test_enum.py", line 11, in <module>
    class SwitchBox(Box):
  File "/home/likern/Projects/PythonGUIGnome/test/test_enum.py", line 18, in SwitchBox
    @GObject.Property(type=SwitchToggleMode, default=SwitchToggleMode.AUTO)
  File "/home/likern/.virtualenvs/photomanager/lib/python3.6/site-packages/gi/_propertyhelper.py", line 155, in __init__
    self._check_default()
  File "/home/likern/.virtualenvs/photomanager/lib/python3.6/site-packages/gi/_propertyhelper.py", line 306, in _check_default
    elif not _gi.GType(default).is_a(ptype):
TypeError: could not get typecode from object