multi key dictionary implementation - Python 2.7

 Implementation of a multi-key dictionary, i.e.:
  (key1[,key2, ..]) => value
 .
 This dictionary has a similar interface to the standard dictionary, but is
 extended to support multiple keys referring to the same element.
 .
 Multi-key dict provides also extended interface for iterating over items and
 keys (e.g. by the key type), which might be useful when creating, e.g.
 dictionaries with index-name key pair allowing to iterate over items using
 either: names or indexes. It can be useful for many other similar use-cases,
 and there is no limit to the number of keys used to map to the value.
 .
 There are few other useful methods, e.g. to iterate over dictionary (by/using)
 selected key type, finding other keys mapping to the same value etc.
 .
 This package contains the Python 2.7 module.