def __init__(self, kind, title, kind_properties, contact_properties=[]):
    """ Ctor.

    title is the name of this particular entity, e.g. Bob Jones or Mom's
    Birthday Party.

    kind_properties is a list of property names that should be included in
    this entity's XML encoding as first-class XML elements, instead of
    <property> elements. 'title' and 'content' are added to kind_properties
    automatically, and may not appear in contact_properties.

    contact_properties is a list of property names that are Keys that point to
    Contact entities, and should be included in this entity's XML encoding as
    <gd:who> elements. If a property name is included in both kind_properties
    and contact_properties, it is treated as a Contact property.

    Args:
    kind: string
    title: string
    kind_properties: list of strings
    contact_properties: list of string
    """
    datastore.Entity.__init__(self, kind)

    if not isinstance(title, types.StringTypes):
      raise datastore_errors.BadValueError(
        'Expected a string for title; received %s (a %s).' %
        (title, datastore_types.typename(title)))
    self['title'] = title
    self['content'] = ''

    self._contact_properties = set(contact_properties)
    assert not self._contact_properties.intersection(self.keys())

    self._kind_properties = self._contact_properties - set(kind_properties)
    self._kind_properties.add('title')
    self._kind_properties.add('content')
dataset/ETHPy150Open CollabQ/CollabQ/.google_appengine/google/appengine/api/datastore_entities.py/GdKind.__init__/swapped operands of `-`