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
Update bag with all elements in iterable.

        >>> s = pbag([1])
        >>> s.update([1, 2])
        pbag([1, 1, 2])