class_docstr: A persistent bag/multiset type.
  
  Requires elements to be hashable, and allows duplicates, but has no
  ordering. Bags are hashable.
  
  Do not instantiate directly, instead use the factory functions :py:func:`b`
  or :py:func:`pbag` to create an instance.
  
  Some examples:
  
  >>> s = pbag([1, 2, 3, 1])
  >>> s2 = s.add(4)
  >>> s3 = s2.remove(1)
  >>> s
  pbag([1, 1, 2, 3])
  >>> s2
  pbag([1, 1, 2, 3, 4])
  >>> s3
  pbag([1, 2, 3, 4])
code: def __init__(self, counts):
      self._counts = counts
  
imports: from collections.abc import Container, Iterable, Sized, Hashable
  from functools import reduce
  from typing import Generic, TypeVar
  from pyrsistent._pmap import pmap
label_desc: Use image node_id 1 to create a new PBag object from inherited base classes: Generic with example: obj = PBag(counts)