def from_obj(cls, obj, return_obj=None):
        from stix.common import StructuredTextList, InformationSource
        from stix.data_marking import Marking

        if not return_obj:
            raise ValueError("Must provide a return_obj argument")

        if not obj:
            raise ValueError("Must provide an obj argument")

        return_obj.id_ = obj.id
        return_obj.idref = obj.idref
        return_obj.timestamp = obj.timestamp

        # These may not be found on the input obj if it isn't a full
        # type definition (e.g., used as a reference)
        return_obj.version = getattr(obj, 'version', None)
        return_obj.title = getattr(obj, 'Title', None)
        return_obj.descriptions = \
            StructuredTextList.from_obj(getattr(obj, 'Description', None))
        return_obj.short_descriptions = \
            StructuredTextList.from_obj(getattr(obj, 'Short_Description', None))
        return_obj.information_source = \
            InformationSource.from_obj(getattr(obj, 'Information_Source', None))
        return_obj.handling = \
            Marking.from_obj(getattr(obj, 'Handling', None))

        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)
        return_obj.applicability_confidence = Confidence.from_obj(obj.Applicability_Confidence)
        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.id_ = dict_repr.get('id')
        return_obj.title = dict_repr.get('title')
        return_obj.descriptions = StructuredTextList.from_dict(dict_repr.get('description'))
        return_obj.short_descriptions = StructuredTextList.from_dict(dict_repr.get('short_description'))

        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.id_ = obj.id
        return_obj.title = obj.Title
        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)

        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None
        if not return_obj:
            return_obj = cls()

        get = dict_repr.get
        return_obj.description = StructuredTextList.from_dict(get('description'))
        return_obj.short_description = StructuredTextList.from_dict(get('short_description'))
        return_obj.applicability_confidence = Confidence.from_dict(get('applicability_confidence'))
        
        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None

        if not return_obj:
            return_obj = cls()

        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_description = StructuredTextList.from_obj(obj.Short_Description)
        return_obj.cce_id = obj.CCE_ID

        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None

        if not return_obj:
            return_obj = cls()

        get = dict_repr.get
        return_obj.descriptions = StructuredTextList.from_dict(get('description'))
        return_obj.short_descriptions = StructuredTextList.from_dict(get('short_description'))
        return_obj.cce_id = get('cce_id')

        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.id_ = dict_repr.get('id')
        return_obj.title = dict_repr.get('title')
        return_obj.descriptions = StructuredTextList.from_dict(dict_repr.get('description'))
        return_obj.short_descriptions = StructuredTextList.from_dict(dict_repr.get('short_description'))
        return_obj.types = [VocabString.from_dict(x) for x in dict_repr.get('types', [])]
        return_obj.observable_characterization = Observables.from_dict(dict_repr.get('observable_characterization'))

        return return_obj

class Sighting(stix.Entity):
    _namespace = "http://stix.mitre.org/Indicator-2"
    _binding = indicator_binding
    _binding_class = _binding.SightingType
    
    timestamp = fields.DateTimeField("timestamp")
    timestamp_precision = fields.TypedField("timestamp_precision", preset_hook=validate_precision)
    descriptions = fields.TypedField("Description", StructuredTextList)
    source = fields.TypedField("Source", InformationSource)
    reference = fields.TypedField("Reference")
    confidence = fields.TypedField("Confidence", Confidence)
    related_observables = fields.TypedField("Related_Observables", type_="stix.indicator.sightings.RelatedObservables")
    
    def __init__(self, timestamp=None, timestamp_precision=None, description=None):
        super(Sighting, self).__init__()

        self.timestamp = timestamp or utils.dates.now()
        self.timestamp_precision = timestamp_precision
        self.descriptions = description
        self.source = None
        self.reference = None
        self.confidence = None

    @property
    def description(self):
        """A single description about the contents or purpose of this object.

        Default Value: ``None``

        Note:
            If this object has more than one description set, this will return
            the description with the lowest ordinality value.

        Returns:
            An instance of :class:`.StructuredText`

        """
        return next(iter(self.descriptions or []), None)

    @description.setter
    def description(self, value):
        self.descriptions = StructuredTextList(value)

    def add_description(self, description):
        """Adds a description to the ``descriptions`` collection.

        This is the same as calling "foo.descriptions.add(bar)".

        """
        self.descriptions.add(description)

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None

        if not return_obj:
            return_obj = cls()

        return_obj.title = obj.Title
        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)
        return_obj.handling = Marking.from_obj(obj.Handling)
        return_obj.information_source = InformationSource.from_obj(obj.Information_Source)
        return_obj.intents = _ReportIntents.from_obj(obj.Intent)

        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None

        if not return_obj:
            return_obj = cls()

        return_obj.title = obj.Title
        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)
        return_obj.handling = Marking.from_obj(obj.Handling)
        return_obj.information_source = InformationSource.from_obj(obj.Information_Source)
        return_obj.package_intents = _PackageIntents.from_obj(obj.Package_Intent)
        return_obj.profiles = obj.Profiles.Profile if obj.Profiles else []

        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.id_ = obj.id
        return_obj.title = obj.Title
        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)
        return_obj.observable_characterization = Observables.from_obj(obj.Observable_Characterization)

        if obj.Type:
            return_obj.types = [VocabString.from_obj(x) for x in obj.Type]

        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None

        if not return_obj:
            return_obj = cls()

        get = dict_repr.get

        return_obj.title = get('title')
        return_obj.intents = _ReportIntents.from_list(get('intents'))
        return_obj.descriptions = StructuredTextList.from_dict(get('description'))
        return_obj.short_descriptions = StructuredTextList.from_dict(get('short_description'))
        return_obj.handling = Marking.from_dict(get('handling'))
        return_obj.information_source = InformationSource.from_dict(get('information_source'))

        return return_obj

    def add_description(self, description):
        """Adds a description to the ``descriptions`` collection.

        This is the same as calling "foo.descriptions.add(bar)".
        """
        if self.descriptions is None:
            self.descriptions = StructuredTextList()
        self.descriptions.add(description)

    def from_dict(cls, d, return_obj=None):
        if not d:
            return None
        if not return_obj:
            return_obj = cls()

        get = d.get
        return_obj.type_ = AssetType.from_dict(get('type'))
        return_obj.descriptions = StructuredTextList.from_dict(get('description'))
        return_obj.business_functions_or_roles = StructuredTextList.from_dict(get('business_function_or_role'))
        return_obj.ownership_class = VocabString.from_dict(get('ownership_class'))
        return_obj.management_class = VocabString.from_dict(get('management_class'))
        return_obj.location_class = VocabString.from_dict(get('location_class'))
        # return_obj.location = Location.from_dict(get('location'))
        return_obj.nature_of_security_effect = NatureOfSecurityEffect.from_dict(get('nature_of_security_effect'))
        return_obj.structured_description = Observables.from_dict(get('structured_description'))
        return return_obj

class GenericTestMechanism(_BaseTestMechanism):
    _namespace = "http://stix.mitre.org/extensions/TestMechanism#Generic-1"
    _binding = generic_tm_binding
    _binding_class = _binding.GenericTestMechanismType
    _XSI_TYPE = "genericTM:GenericTestMechanismType"
    
    reference_location = fields.TypedField("reference_location")
    descriptions = fields.TypedField("Description", StructuredTextList)
    specification = fields.TypedField("Specification", EncodedCDATA)
    type_ = VocabField("Type")
    
    def __init__(self, id_=None, idref=None):
        super(GenericTestMechanism, self).__init__(id_=id_, idref=idref)
        self.descriptions = StructuredTextList()

    @property
    def description(self):
        """A single description about the contents or purpose of this object.

        Default Value: ``None``

        Note:
            If this object has more than one description set, this will return
            the description with the lowest ordinality value.

        Returns:
            An instance of
            :class:`.StructuredText`

        """
        return next(iter(self.descriptions), None)

    @description.setter
    def description(self, value):
        self.descriptions = StructuredTextList(value)

    def add_description(self, description):
        """Adds a description to the ``descriptions`` collection.

        This is the same as calling "foo.descriptions.add(bar)".

        """
        if self.descriptions is None:
            self.descriptions = StructuredTextList()
        self.descriptions.add(description)

    def from_obj(cls, obj, return_obj=None):
        import stix.extensions.malware.maec_4_1_malware  # noqa
        
        if not obj:
            return None
        
        if not return_obj:
            klass = stix.lookup_extension(obj, default=cls)
            return_obj = klass.from_obj(obj, klass())
        else:
            return_obj.id_ = obj.id
            return_obj.title = obj.Title
            return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
            return_obj.short_descriptions = StructuredTextList.from_obj(obj.Short_Description)
            return_obj.names = MalwareNames.from_obj(obj.Name)
            return_obj.types = MalwareTypes.from_obj(obj.Type)

        return return_obj

    def from_dict(cls, d, return_obj=None):
        from stix.common import StructuredTextList, InformationSource
        from stix.data_marking import Marking

        if not return_obj:
            raise ValueError("Must provide a return_obj argument")

        get = d.get
        return_obj.id_ = get("id")
        return_obj.idref = get("idref")
        return_obj.timestamp = get("timestamp")
        return_obj.version = get("version")
        return_obj.title = get("title")
        return_obj.descriptions = StructuredTextList.from_dict(get("description"))
        return_obj.short_descriptions = StructuredTextList.from_dict(get("short_description"))
        return_obj.information_source = InformationSource.from_dict(get("information_source"))
        return_obj.handling = Marking.from_dict(get("handling"))

        return return_obj

    def from_dict(cls, dict_repr, return_obj=None):
        if not dict_repr:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.descriptions = StructuredTextList.from_dict(dict_repr.get('description'))
        return_obj.cwe_id = dict_repr.get('cwe_id')

        return return_obj

    def from_obj(cls, obj, return_obj=None):
        if not obj:
            return None
        if not return_obj:
            return_obj = cls()

        return_obj.type_ = AssetType.from_obj(obj.Type)
        return_obj.descriptions = StructuredTextList.from_obj(obj.Description)
        return_obj.business_functions_or_roles = StructuredTextList.from_obj(obj.Business_Function_Or_Role)
        return_obj.ownership_class = VocabString.from_obj(obj.Ownership_Class)
        return_obj.management_class = VocabString.from_obj(obj.Management_Class)
        return_obj.location_class = VocabString.from_obj(obj.Location_Class)
        # return_obj.location = None
        
        if obj.Nature_Of_Security_Effect:
            n = obj.Nature_Of_Security_Effect
            return_obj.nature_of_security_effect = [PropertyAffected.from_obj(x) for x in n.Property_Affected]

        return return_obj