How to use the pyrsistent._pbag.PBag function in pyrsistent

def pbag(elements):
    """
    Convert an iterable to a persistent bag.

    Takes an iterable with elements to insert.

    >>> pbag([1, 2, 3, 2])
    pbag([1, 2, 2, 3])
    """
    if not elements:
        return _EMPTY_PBAG
    return PBag(reduce(_add_to_counters, elements, pmap()))

def __and__(self, other):
        """
        Intersection: Only keep elements that are present in both PBags.
        
        >>> pbag([1, 2, 2, 2]) & pbag([2, 3, 3])
        pbag([2])
        """
        if not isinstance(other, PBag):
            return NotImplemented
        result = pmap().evolver()
        for elem, count in self._counts.iteritems():
            newcount = min(count, other.count(elem))
            if newcount > 0:
                result[elem] = newcount
        return PBag(result.persistent())

def update(self, iterable):
        """
        Update bag with all elements in iterable.

        >>> s = pbag([1])
        >>> s.update([1, 2])
        pbag([1, 1, 2])
        """
        if iterable:
            return PBag(reduce(_add_to_counters, iterable, self._counts))

        return self

def pbag(elements):
    """
    Convert an iterable to a persistent bag.

    Takes an iterable with elements to insert.

    >>> pbag([1, 2, 3, 2])
    pbag([1, 2, 2, 3])
    """
    if not elements:
        return _EMPTY_PBAG
    return PBag(reduce(_add_to_counters, elements, pmap()))


_EMPTY_PBAG = PBag(pmap())

>>> s = pbag([1, 1, 2])
        >>> s2 = s.remove(1)
        >>> s3 = s.remove(2)
        >>> s2
        pbag([1, 2])
        >>> s3
        pbag([1, 1])
        """
        if element not in self._counts:
            raise KeyError(element)
        elif self._counts[element] == 1:
            newc = self._counts.remove(element)
        else:
            newc = self._counts.set(element, self._counts[element] - 1)
        return PBag(newc)

def __or__(self, other):
        """ 
        Union: Keep elements that are present in either of two PBags.

        >>> pbag([1, 2, 2, 2]) | pbag([2, 3, 3])
        pbag([1, 2, 2, 2, 3, 3])
        """
        if not isinstance(other, PBag):
            return NotImplemented
        result = self._counts.evolver()
        for elem, other_count in other._counts.iteritems():
            count = self.count(elem)
            newcount = max(count, other_count)
            result[elem] = newcount
        return PBag(result.persistent())

"""
        Hash based on value of elements.

        >>> m = pmap({pbag([1, 2]): "it's here!"})
        >>> m[pbag([2, 1])]
        "it's here!"
        >>> pbag([1, 1, 2]) in m
        False
        """
        return hash(self._counts)


Container.register(PBag)
Iterable.register(PBag)
Sized.register(PBag)
Hashable.register(PBag)


def b(*elements):
    """
    Construct a persistent bag.

    Takes an arbitrary number of arguments to insert into the new persistent
    bag.

    >>> b(1, 2, 3, 2)
    pbag([1, 2, 2, 3])
    """
    return pbag(elements)


def pbag(elements):

def __add__(self, other):
        """ 
        Combine elements from two PBags.

        >>> pbag([1, 2, 2]) + pbag([2, 3, 3])
        pbag([1, 2, 2, 2, 3, 3])
        """
        if not isinstance(other, PBag):
            return NotImplemented
        result = self._counts.evolver()
        for elem, other_count in other._counts.iteritems():
            result[elem] = self.count(elem) + other_count
        return PBag(result.persistent())

def __add__(self, other):
        """ 
        Combine elements from two PBags.

        >>> pbag([1, 2, 2]) + pbag([2, 3, 3])
        pbag([1, 2, 2, 2, 3, 3])
        """
        if not isinstance(other, PBag):
            return NotImplemented
        result = self._counts.evolver()
        for elem, other_count in other._counts.iteritems():
            result[elem] = self.count(elem) + other_count
        return PBag(result.persistent())