FrozenDict is unmodifiable dict-like object (like tuple) and therefore can be easy share between object or functions
without making copy. State of object (it's contents) is set in init and then cannot be changed (so called "frozen").
All functions works fine in both Python 2 and 3 thanks to collections.Mapping class, which encapsulate all differences
between Python versions (like viewitems in Python 2 renamed to items in Python 3).
It can be created like dict objects (it simply use dict object in __init__) and have same functions like dict, without
methods to mutate state like __setitem__. Also unlike dict, the FrozenDict has __hash__ implementation, so that it can
be use in hash required places (like dict keys).
.. autoclass:: dicttools.FrozenDict
:members: __init__
The ChainMap is similar to collections.ChainMap, but cannot be used as replacement. There are a few important
differences. This ChainMap is designed as view for iterable (list, tuple, MappingView, etc.) of maps (dict or
other Mapping). ChainMap allow to get, set, or delete items in dicts. When value cannot be founded, KeyException is raised.
Given maps is encapsulated inside ChainMap and cannot be called directly. For chaining maps directly keep object separately.
Each modification in maps automatically affect the chain, because maps is contained as reference (not as copy).
.. autoclass:: dicttools.ChainMap
:members: __init__
TwoWayDict is container for storing pairs key-value with additional reversed access.
It means, when you assign value to key, the key can be also accessible by value.
Is important to handle both keys and variables as hashable.
.. autoclass:: dicttools.TwoWayDict
:members: __init__