Python builtins.property() Examples

def violation(self):
        """Amount that current solution violates this constraint

        If a solution is available, than this property indicates how much
        the current solution violates this constraint.
        """
        lhs = sum(coef * var.x for (var, coef) in self.__expr.items())
        rhs = -self.const
        if self.sense == "=":
            viol = abs(lhs - rhs)
        elif self.sense == "<":
            viol = max(lhs - rhs, 0.0)
        elif self.sense == ">":
            viol = max(rhs - lhs, 0.0)
        else:
            raise ValueError("Invalid sense {}".format(self.sense))

        return viol 

def clone_properties(self, src, proplist=None):
        '''Clone properties from other object.

        :param PropertyHolder src: source object
        :param iterable proplist: list of properties \
            (:py:obj:`None` or omit for all properties except those with \
            :py:attr:`property.clone` set to :py:obj:`False`)
        '''

        if proplist is None:
            proplist = [prop for prop in self.property_list()
                if prop.clone]
        else:
            proplist = [prop for prop in self.property_list()
                if prop.__name__ in proplist or prop in proplist]

        for prop in proplist:
            try:
                # pylint: disable=protected-access
                self._property_init(prop, getattr(src, prop._attr_name))
            except AttributeError:
                continue

        self.fire_event('clone-properties', src=src, proplist=proplist) 

def load_properties(self, load_stage=None):
        '''Load properties from immediate children of XML node.

        ``property-set`` events are not fired for each individual property.

        :param int load_stage: Stage of loading.
        '''

        if self.xml is None:
            return
        all_names = set(
            prop.__name__ for prop in self.property_list(load_stage))
        for node in self.xml.xpath('./properties/property'):
            name = node.get('name')
            value = node.get('ref') or node.text

            if not name in all_names:
                continue

            setattr(self, name, value) 

def property_get_def(cls, prop):
        '''Return property definition object.

        If prop is already :py:class:`qubes.property` instance, return the same
        object.

        :param prop: property object or name
        :type prop: qubes.property or str
        :rtype: qubes.property
        '''

        if isinstance(prop, qubes.property):
            return prop

        props = cls.property_dict()
        if prop in props:
            return props[prop]

        raise AttributeError('No property {!r} found in {!r}'.format(
            prop, cls)) 

def property_is_default(self, prop):
        '''Check whether property is in it's default value.

        Properties when unset may return some default value, so
        ``hasattr(vm, prop.__name__)`` is wrong in some circumstances. This
        method allows for checking if the value returned is in fact it's
        default value.

        :param qubes.property prop: property object of particular interest
        :rtype: bool
        ''' # pylint: disable=protected-access

        # both property_get_def() and ._attr_name may throw AttributeError,
        # which we don't want to catch
        attrname = self.property_get_def(prop)._attr_name
        return not hasattr(self, attrname) 

def __init__(self, name, setter=None, saver=None, type=None,
            default=_NO_DEFAULT, write_once=False, load_stage=2, order=0,
            save_via_ref=False, clone=True,
            doc=None):
        # pylint: disable=redefined-builtin
        self.__name__ = name
        if setter is None and type is bool:
            setter = qubes.property.bool
        self._setter = setter
        self._saver = saver if saver is not None else (
            lambda self, prop, value: str(value))
        self.type = type
        self._default = default
        self._default_function = None
        if isinstance(default, collections.abc.Callable):
            self._default_function = default

        self._write_once = write_once
        self.order = order
        self.load_stage = load_stage
        self.save_via_ref = save_via_ref
        self.clone = clone
        self.__doc__ = doc
        self._attr_name = '_qubesprop_' + name 

def property_dict(cls, load_stage=None):
        '''List all properties attached to this VM's class

        :param load_stage: Filter by load stage
        :type load_stage: :py:func:`int` or :py:obj:`None`
        '''

        # use cls.__dict__ since we must not look at parent classes
        if "_property_dict" not in cls.__dict__:
            cls._property_dict = {}
        memo = cls._property_dict

        if load_stage not in memo:
            props = dict()
            if load_stage is None:
                for class_ in cls.__mro__:
                    for name in class_.__dict__:
                        # don't overwrite props with those from base classes
                        if name not in props:
                            prop = class_.__dict__[name]
                            if isinstance(prop, property):
                                assert name == prop.__name__
                                props[name] = prop
            else:
                for prop in cls.property_dict().values():
                    if prop.load_stage == load_stage:
                        props[prop.__name__] = prop
            memo[load_stage] = props

        return memo[load_stage] 

def produce_immutables_list(json_doc):
    immutables_list = []
    for property in json_doc:
        # Add only readonly attributes
        if not property['is_updateable']:
            immutables_list.append(property['option_name'])
    return immutables_list 

def produce_readwrite_attrs_list(json_doc):
    readwrite_attrs  = list()
    for property in json_doc:
        readwrite_attrs .append(property['option_name'])
    return readwrite_attrs 

def produce_module_arguments_from_json_schema(json_doc, skip_attrs):
    module_arguments = list()
    for property in json_doc:

        # Skip attributes in skip_attrs
        if property['option_name'] in skip_attrs:
            continue

        key = property['option_name']
        entry = {}
        entry['key'] = key
        entry['transforms'] = []

        # Convert json type to ansible module argument type declaration

        entry['type'] = property['type']

        # Add choices if applicable
        if 'choices' in property:
            choice_set = frozenset([choice.lower() for choice in property['choices']])
            if choice_set == frozenset(['yes', 'no']):
                # Overwrite type to bool
                entry['type'] = 'bool'
                entry['transforms'] = ['bool_yes_no']
            elif choice_set == frozenset(['on', 'off']):
                # Overwrite type to bool
                entry['type'] = 'bool'
                entry['transforms'] = ['bool_on_off']
            elif choice_set == frozenset(['enabled', 'disabled']):
                entry['choices'] = ['enabled', 'disabled']
            else:
                entry['choices'] = property['choices']

        # Add to ansible modules argument
        module_arguments.append(entry)

    return module_arguments 

def property_require(self, prop, allow_none=False, hard=False):
        '''Complain badly when property is not set.

        :param prop: property name or object
        :type prop: qubes.property or str
        :param bool allow_none: if :py:obj:`True`, don't complain if \
            :py:obj:`None` is found
        :param bool hard: if :py:obj:`True`, raise :py:class:`AssertionError`; \
            if :py:obj:`False`, log warning instead
        '''

        if isinstance(prop, qubes.property):
            prop = prop.__name__

        try:
            value = getattr(self, prop)
            if value is None and not allow_none:
                msg = 'Property {!r} cannot be None'.format(prop)
                if hard:
                    raise ValueError(msg)
                self.log.fatal(msg)
        except AttributeError:
            # pylint: disable=no-member
            msg = 'Required property {!r} not set on {!r}'.format(prop, self)
            if hard:
                raise ValueError(msg)
            # pylint: disable=no-member
            self.log.fatal(msg) 

def xml_properties(self, with_defaults=False):
        '''Iterator that yields XML nodes representing set properties.

        :param bool with_defaults: If :py:obj:`True`, then it also includes \
            properties which were not set explicite, but have default values \
            filled.
        '''


        properties = lxml.etree.Element('properties')

        for prop in self.property_list():
            # pylint: disable=protected-access
            try:
                value = getattr(
                    self, (prop.__name__ if with_defaults else prop._attr_name))
            except AttributeError:
                continue

            try:
                value = prop._saver(self, prop, value)
            except property.DontSave:
                continue

            element = lxml.etree.Element('property', name=prop.__name__)
            if prop.save_via_ref:
                element.set('ref', value)
            else:
                element.text = value
            properties.append(element)

        return properties


    # this was clone_attrs 

def _property_init(self, prop, value):
        '''Initialise property to a given value, without side effects.

        :param qubes.property prop: property object of particular interest
        :param value: value
        '''

        # pylint: disable=protected-access
        setattr(self, self.property_get_def(prop)._attr_name, value) 

def __init__(self, xml, **kwargs):
        self.xml = xml

        propvalues = {}

        all_names = self.property_dict()
        for key in list(kwargs):
            if not key in all_names:
                continue
            propvalues[key] = kwargs.pop(key)

        super(PropertyHolder, self).__init__(**kwargs)

        for key, value in propvalues.items():
            setattr(self, key, value)

        if self.xml is not None:
            # check if properties are appropriate
            for node in self.xml.xpath('./properties/property'):
                name = node.get('name')
                if name not in all_names:
                    raise TypeError(
                        'property {!r} not applicable to {!r}'.format(
                            name, self.__class__.__name__))

    # pylint: disable=too-many-nested-blocks 

def stateless_property(func):
    '''Decorator similar to :py:class:`builtins.property`, but for properties
    exposed through management API (including qvm-prefs etc)'''
    return property(func.__name__,
        setter=property.forbidden,
        saver=property.dontsave,
        default=func,
        doc=func.__doc__) 

def forbidden(self, prop, value):
        '''Property setter that forbids loading a property.

        This is used to effectively disable property in classes which inherit
        unwanted property. When someone attempts to load such a property, it

        :throws AttributeError: always
        ''' # pylint: disable=bad-staticmethod-argument,unused-argument

        raise AttributeError(
            'setting {} property on {} instance is forbidden'.format(
                prop.__name__, self.__class__.__name__)) 

def dontsave(self, prop, value):
        '''Dummy saver that never saves anything.'''
        # pylint: disable=bad-staticmethod-argument,unused-argument
        raise property.DontSave()

    #
    # some setters provided
    # 

def sanitize(self, *, untrusted_newvalue):
        '''Coarse sanitization of value to be set, before sending it to a
        setter. Can raise QubesValueError if the value is invalid.

        :param untrusted_newvalue: value to be validated
        :return: sanitized value
        :raises: qubes.exc.QubesValueError
        '''
        # do not treat type='str' as sufficient validation
        if self.type is not None and self.type is not str:
            # assume specific type will preform enough validation
            try:
                untrusted_newvalue = untrusted_newvalue.decode('ascii',
                    errors='strict')
            except UnicodeDecodeError:
                raise qubes.exc.QubesValueError
            if self.type is bool:
                return self.bool(None, None, untrusted_newvalue)
            try:
                return self.type(untrusted_newvalue)
            except ValueError:
                raise qubes.exc.QubesValueError
        else:
            # 'str' or not specified type
            try:
                untrusted_newvalue = untrusted_newvalue.decode('ascii',
                    errors='strict')
            except UnicodeDecodeError:
                raise qubes.exc.QubesValueError
            allowed_set = string.printable
            if not all(x in allowed_set for x in untrusted_newvalue):
                raise qubes.exc.QubesValueError(
                    'Invalid characters in property value')
            return untrusted_newvalue


    #
    # exceptions
    # 

def _enforce_write_once(self, instance):
        if self._write_once and not instance.property_is_default(self):
            raise AttributeError(
                'property {!r} is write-once and already set'.format(
                    self.__name__)) 

def __eq__(self, other):
        if isinstance(other, str):
            return self.__name__ == other
        return isinstance(other, property) and self.__name__ == other.__name__ 

def __delete__(self, instance):
        self._enforce_write_once(instance)

        try:
            oldvalue = getattr(instance, self.__name__)
            has_oldvalue = True
        except AttributeError:
            has_oldvalue = False

        if has_oldvalue:
            instance.fire_event('property-pre-reset:' + self.__name__,
                pre_event=True,
                name=self.__name__, oldvalue=oldvalue)
            # deprecated, to be removed in Qubes 5.0
            instance.fire_event('property-pre-del:' + self.__name__,
                pre_event=True,
                name=self.__name__, oldvalue=oldvalue)
            try:
                delattr(instance, self._attr_name)
            except AttributeError:
                pass
            instance.fire_event('property-reset:' + self.__name__,
                name=self.__name__, oldvalue=oldvalue)
            # deprecated, to be removed in Qubes 5.0
            instance.fire_event('property-del:' + self.__name__,
                name=self.__name__, oldvalue=oldvalue)

        else:
            instance.fire_event('property-pre-reset:' + self.__name__,
                pre_event=True,
                name=self.__name__)
            # deprecated, to be removed in Qubes 5.0
            instance.fire_event('property-pre-del:' + self.__name__,
                pre_event=True,
                name=self.__name__)
            instance.fire_event('property-reset:' + self.__name__,
                name=self.__name__)
            # deprecated, to be removed in Qubes 5.0
            instance.fire_event('property-del:' + self.__name__,
                name=self.__name__) 

def __set__(self, instance, value):
        self._enforce_write_once(instance)

        if value is self.__class__.DEFAULT:
            self.__delete__(instance)
            return

        try:
            oldvalue = getattr(instance, self.__name__)
            has_oldvalue = True
        except AttributeError:
            has_oldvalue = False

        if self._setter is not None:
            value = self._setter(instance, self, value)
        if self.type not in (None, type(value)):
            value = self.type(value)

        if has_oldvalue:
            instance.fire_event('property-pre-set:' + self.__name__,
                pre_event=True,
                name=self.__name__, newvalue=value, oldvalue=oldvalue)
        else:
            instance.fire_event('property-pre-set:' + self.__name__,
                pre_event=True,
                name=self.__name__, newvalue=value)

        instance._property_init(self, value)  # pylint: disable=protected-access

        if has_oldvalue:
            instance.fire_event('property-set:' + self.__name__,
                name=self.__name__, newvalue=value, oldvalue=oldvalue)
        else:
            instance.fire_event('property-set:' + self.__name__,
                name=self.__name__, newvalue=value) 

def get_default(self, instance):
        if self._default is self._NO_DEFAULT:
            raise AttributeError(
                'property {!r} have no default'.format(self.__name__))
        if self._default_function:
            return self._default_function(instance)
        return self._default 

def __get__(self, instance, owner):
        if instance is None:
            return self

        # XXX this violates duck typing, shall we keep it?
        if not isinstance(instance, PropertyHolder):
            raise AttributeError('qubes.property should be used on '
                'qubes.PropertyHolder instances only')

        try:
            return getattr(instance, self._attr_name)

        except AttributeError:
            return self.get_default(instance)