How to use the pyrsistent._pvector.PythonPVector function in pyrsistent

def append(self, val):
        if len(self._tail) < BRANCH_FACTOR:
            new_tail = list(self._tail)
            new_tail.append(val)
            return PythonPVector(self._count + 1, self._shift, self._root, new_tail)

        # Full tail, push into tree
        new_root, new_shift = self._create_new_root()
        return PythonPVector(self._count + 1, new_shift, new_root, [val])

# a ~5 X performance penalty on PyPy (considered the primary platform for this implementation
        #  of PVector) so we're keeping this implementation for now.

        if not isinstance(i, Integral):
            raise TypeError("'%s' object cannot be interpreted as an index" % type(i).__name__)

        if i < 0:
            i += self._count

        if 0 <= i < self._count:
            if i >= self._tail_offset:
                new_tail = list(self._tail)
                new_tail[i & BIT_MASK] = val
                return PythonPVector(self._count, self._shift, self._root, new_tail)

            return PythonPVector(self._count, self._shift, self._do_set(self._shift, self._root, i, val), self._tail)

        if i == self._count:
            return self.append(val)

        raise IndexError("Index out of range: %s" % (i,))

def append(self, val):
        if len(self._tail) < BRANCH_FACTOR:
            new_tail = list(self._tail)
            new_tail.append(val)
            return PythonPVector(self._count + 1, self._shift, self._root, new_tail)

        # Full tail, push into tree
        new_root, new_shift = self._create_new_root()
        return PythonPVector(self._count + 1, new_shift, new_root, [val])

def __getitem__(self, index):
            if not isinstance(index, Integral):
                raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__)

            if index < 0:
                index += self._count + len(self._extra_tail)

            if self._count <= index < self._count + len(self._extra_tail):
                return self._extra_tail[index - self._count]

            return PythonPVector._node_for(self, index)[index & BIT_MASK]

if isinstance(source_data, cls):
        return source_data

    # Recursively apply create methods of checked types if the types of the supplied data
    # does not match any of the valid types.
    types = get_types(cls._checked_types)
    checked_type = next((t for t in types if issubclass(t, CheckedType)), None)
    if checked_type:
        return cls([checked_type.create(data, ignore_extra=ignore_extra)
                    if not any(isinstance(data, t) for t in types) else data
                    for data in source_data])

    return cls(source_data)

@six.add_metaclass(_CheckedTypeMeta)
class CheckedPVector(PythonPVector, CheckedType):
    """
    A CheckedPVector is a PVector which allows specifying type and invariant checks.

    >>> class Positives(CheckedPVector):
    ...     __type__ = (long, int)
    ...     __invariant__ = lambda n: (n >= 0, 'Negative')
    ...
    >>> Positives([1, 2, 3])
    Positives([1, 2, 3])
    """

    __slots__ = ()

    def __new__(cls, initial=()):
        if type(initial) == PythonPVector:
            return super(CheckedPVector, cls).__new__(cls, initial._count, initial._shift, initial._root, initial._tail)