How to use the pyrsistent._pmap.PMap function in pyrsistent

return cls(_factory_fields=_factory_fields, **kwargs)

    def __reduce__(self):
        # Pickling support
        return _restore_pickle, (self.__class__, dict(self),)

    def serialize(self, format=None):
        """
        Serialize the current PRecord using custom serializer functions for fields where
        such have been supplied.
        """
        return dict((k, serialize(self._precord_fields[k].serializer, format, v)) for k, v in self.items())


class _PRecordEvolver(PMap._Evolver):
    __slots__ = ('_destination_cls', '_invariant_error_codes', '_missing_fields', '_factory_fields')

    def __init__(self, cls, original_pmap, _factory_fields=None):
        super(_PRecordEvolver, self).__init__(original_pmap)
        self._destination_cls = cls
        self._invariant_error_codes = []
        self._missing_fields = []
        self._factory_fields = _factory_fields

    def __setitem__(self, key, original_value):
        self.set(key, original_value)

    def set(self, key, original_value):
        field = self._destination_cls._precord_fields.get(key)
        if field:
            if self._factory_fields is None or field in self._factory_fields:

store_invariants(dct, bases, '_precord_invariants', '__invariant__')

        dct['_precord_mandatory_fields'] = \
            set(name for name, field in dct['_precord_fields'].items() if field.mandatory)

        dct['_precord_initial_values'] = \
            dict((k, field.initial) for k, field in dct['_precord_fields'].items() if field.initial is not PFIELD_NO_INITIAL)


        dct['__slots__'] = ()

        return super(_PRecordMeta, mcs).__new__(mcs, name, bases, dct)


@six.add_metaclass(_PRecordMeta)
class PRecord(PMap, CheckedType):
    """
    A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
    from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
    access using subscript notation.

    More documentation and examples of PRecord usage is available at https://github.com/tobgu/pyrsistent
    """
    def __new__(cls, **kwargs):
        # Hack total! If these two special attributes exist that means we can create
        # ourselves. Otherwise we need to go through the Evolver to create the structures
        # for us.
        if '_precord_size' in kwargs and '_precord_buckets' in kwargs:
            return super(PRecord, cls).__new__(cls, kwargs['_precord_size'], kwargs['_precord_buckets'])

        factory_fields = kwargs.pop('_factory_fields', None)

def __new__(cls, size, buckets):
        self = super(PMap, cls).__new__(cls)
        self._size = size
        self._buckets = buckets
        return self

checked_key_type = next((t for t in key_types if issubclass(t, CheckedType)), None)
        value_types = get_types(cls._checked_value_types)
        checked_value_type = next((t for t in value_types if issubclass(t, CheckedType)), None)

        if checked_key_type or checked_value_type:
            return cls(dict((checked_key_type.create(key) if checked_key_type and not any(isinstance(key, t) for t in key_types) else key,
                             checked_value_type.create(value) if checked_value_type and not any(isinstance(value, t) for t in value_types) else value)
                            for key, value in source_data.items()))

        return cls(source_data)

    def __reduce__(self):
        # Pickling support
        return _restore_pickle, (self.__class__, dict(self),)

    class Evolver(PMap._Evolver):
        __slots__ = ('_destination_class', '_invariant_errors')

        def __init__(self, destination_class, original_map):
            super(CheckedPMap.Evolver, self).__init__(original_map)
            self._destination_class = destination_class
            self._invariant_errors = []

        def set(self, key, value):
            _check_types([key], self._destination_class._checked_key_types, self._destination_class, CheckedKeyTypeError)
            _check_types([value], self._destination_class._checked_value_types, self._destination_class)
            self._invariant_errors.extend(data for valid, data in (invariant(key, value)
                                                                   for invariant in self._destination_class._checked_invariants)
                                          if not valid)

            return super(CheckedPMap.Evolver, self).set(key, value)

def persistent(self):
            if self.is_dirty():
                self._original_pmap = PMap(self._size, self._buckets_evolver.persistent())

            return self._original_pmap

store_invariants(dct, bases, '_precord_invariants', '__invariant__')

        dct['_precord_mandatory_fields'] = \
            set(name for name, field in dct['_precord_fields'].items() if field.mandatory)

        dct['_precord_initial_values'] = \
            dict((k, field.initial) for k, field in dct['_precord_fields'].items() if field.initial is not PFIELD_NO_INITIAL)


        dct['__slots__'] = ()

        return super(_PRecordMeta, mcs).__new__(mcs, name, bases, dct)


@six.add_metaclass(_PRecordMeta)
class PRecord(PMap, CheckedType):
    """
    A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
    from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
    access using subscript notation.

    More documentation and examples of PRecord usage is available at https://github.com/tobgu/pyrsistent
    """
    def __new__(cls, **kwargs):
        # Hack total! If these two special attributes exist that means we can create
        # ourselves. Otherwise we need to go through the Evolver to create the structures
        # for us.
        if '_precord_size' in kwargs and '_precord_buckets' in kwargs:
            return super(PRecord, cls).__new__(cls, kwargs['_precord_size'], kwargs['_precord_buckets'])

        factory_fields = kwargs.pop('_factory_fields', None)

def __eq__(self, other):
        if self is other:
            return True
        if not isinstance(other, Mapping):
            return NotImplemented
        if len(self) != len(other):
            return False
        if isinstance(other, PMap):
            if (hasattr(self, '_cached_hash') and hasattr(other, '_cached_hash')
                    and self._cached_hash != other._cached_hash):
                return False
            if self._buckets == other._buckets:
                return True
            return dict(self.iteritems()) == dict(other.iteritems())
        elif isinstance(other, dict):
            return dict(self.iteritems()) == other
        return dict(self.iteritems()) == dict(six.iteritems(other))