mopidy.models.immutable — Mopidy 2.0.0 documentation

# Source code for mopidy.models.immutable

    from __future__ import absolute_import, unicode_literals

    import copy
    import itertools
    import weakref

    from mopidy.internal import deprecation
    from mopidy.models.fields import Field

    class ImmutableObject(object):
        """
        Superclass for immutable objects whose fields can only be modified via the
        constructor.

        This version of this class has been retained to avoid breaking any clients
        relying on it's behavior. Internally in Mopidy we now use
        :class:`ValidatedImmutableObject` for type safety and it's much smaller
        memory footprint.

        :param kwargs: kwargs to set as fields on the object
        :type kwargs: any
        """

        # Any sub-classes that don't set slots won't be effected by the base using
        # slots as they will still get an instance dict.
        __slots__ = ['__weakref__']

        def __init__(self, *args, **kwargs):
            for key, value in kwargs.items():
                if not self._is_valid_field(key):
                    raise TypeError(
                        '__init__() got an unexpected keyword argument "%s"' % key)
                self._set_field(key, value)

        def __setattr__(self, name, value):
            if name.startswith('_'):
                object.__setattr__(self, name, value)
            else:
                raise AttributeError('Object is immutable.')

        def __delattr__(self, name):
            if name.startswith('_'):
                object.__delattr__(self, name)
            else:
                raise AttributeError('Object is immutable.')

        def _is_valid_field(self, name):
            return hasattr(self, name) and not callable(getattr(self, name))

        def _set_field(self, name, value):
            if value == getattr(self.__class__, name):
                self.__dict__.pop(name, None)
            else:
                self.__dict__[name] = value

        def _items(self):
            return self.__dict__.iteritems()

        def __repr__(self):
            kwarg_pairs = []
            for key, value in sorted(self._items()):
                if isinstance(value, (frozenset, tuple)):
                    if not value:
                        continue
                    value = list(value)
                kwarg_pairs.append('%s=%s' % (key, repr(value)))
            return '%(classname)s(%(kwargs)s)' % {
                'classname': self.__class__.__name__,
                'kwargs': ', '.join(kwarg_pairs),
            }

        def __hash__(self):
            hash_sum = 0
            for key, value in self._items():
                hash_sum += hash(key) + hash(value)
            return hash_sum

        def __eq__(self, other):
            if not isinstance(other, self.__class__):
                return False
            return all(a == b for a, b in itertools.izip_longest(
                self._items(), other._items(), fillvalue=object()))

        def __ne__(self, other):
            return not self.__eq__(other)

        def copy(self, **values):
            """
            .. deprecated:: 1.1
                Use :meth:`replace` instead.
            """
            deprecation.warn('model.immutable.copy')
            return self.replace(**values)

        def replace(self, **kwargs):
            """
            Replace the fields in the model and return a new instance

            Examples::

                # Returns a track with a new name
                Track(name='foo').replace(name='bar')
                # Return an album with a new number of tracks
                Album(num_tracks=2).replace(num_tracks=5)

            :param kwargs: kwargs to set as fields on the object
            :type kwargs: any
            :rtype: instance of the model with replaced fields
            """
            other = copy.copy(self)
            for key, value in kwargs.items():
                if not self._is_valid_field(key):
                    raise TypeError(
                        'replace() got an unexpected keyword argument "%s"' % key)
                other._set_field(key, value)
            return other

        def serialize(self):
            data = {}
            data['__model__'] = self.__class__.__name__
            for key, value in self._items():
                if isinstance(value, (set, frozenset, list, tuple)):
                    value = [
                        v.serialize() if isinstance(v, ImmutableObject) else v
                        for v in value]
                elif isinstance(value, ImmutableObject):
                    value = value.serialize()
                if not (isinstance(value, list) and len(value) == 0):
                    data[key] = value
            return data

    class _ValidatedImmutableObjectMeta(type):

        """Helper that initializes fields, slots and memoizes instance creation."""

        def __new__(cls, name, bases, attrs):
            fields = {}

            for base in bases:  # Copy parent fields over to our state
                fields.update(getattr(base, '_fields', {}))

            for key, value in attrs.items():  # Add our own fields
                if isinstance(value, Field):
                    fields[key] = '_' + key
                    value._name = key

            attrs['_fields'] = fields
            attrs['_instances'] = weakref.WeakValueDictionary()
            attrs['__slots__'] = list(attrs.get('__slots__', [])) + fields.values()

            return super(_ValidatedImmutableObjectMeta, cls).__new__(
                cls, name, bases, attrs)

        def __call__(cls, *args, **kwargs):  # noqa: N805
            instance = super(_ValidatedImmutableObjectMeta, cls).__call__(
                *args, **kwargs)
            return cls._instances.setdefault(weakref.ref(instance), instance)

    class ValidatedImmutableObject(ImmutableObject):
        """
        Superclass for immutable objects whose fields can only be modified via the
        constructor. Fields should be :class:`Field` instances to ensure type
        safety in our models.

        Note that since these models can not be changed, we heavily memoize them
        to save memory. So constructing a class with the same arguments twice will
        give you the same instance twice.
        """

        __metaclass__ = _ValidatedImmutableObjectMeta
        __slots__ = ['_hash']

        def __hash__(self):
            if not hasattr(self, '_hash'):
                hash_sum = super(ValidatedImmutableObject, self).__hash__()
                object.__setattr__(self, '_hash', hash_sum)
            return self._hash

        def _is_valid_field(self, name):
            return name in self._fields

        def _set_field(self, name, value):
            object.__setattr__(self, name, value)

        def _items(self):
            for field, key in self._fields.items():
                if hasattr(self, key):
                    yield field, getattr(self, key)

        def replace(self, **kwargs):
            """
            Replace the fields in the model and return a new instance

            Examples::

                # Returns a track with a new name
                Track(name='foo').replace(name='bar')
                # Return an album with a new number of tracks
                Album(num_tracks=2).replace(num_tracks=5)

            Note that internally we memoize heavily to keep memory usage down given
            our overly repetitive data structures. So you might get an existing
            instance if it contains the same values.

            :param kwargs: kwargs to set as fields on the object
            :type kwargs: any
            :rtype: instance of the model with replaced fields
            """
            if not kwargs:
                return self
            other = super(ValidatedImmutableObject, self).replace(**kwargs)
            if hasattr(self, '_hash'):
                object.__delattr__(other, '_hash')
            return self._instances.setdefault(weakref.ref(other), other)