3 # © Copyright 2021-2022, Scott Gasch
5 """A bidirectional dictionary."""
9 def __init__(self, *args, **kwargs):
11 A class that stores both a Mapping between keys and values and
12 also the inverse mapping between values and their keys to
13 allow for efficient lookups in either direction. Because it
14 is possible to have several keys with the same value, using
15 the inverse map returns a sequence of keys.
36 super().__init__(*args, **kwargs)
38 for key, value in self.items():
39 self.inverse.setdefault(value, []).append(key)
41 def __setitem__(self, key, value):
44 self.inverse[old_value].remove(key)
45 super().__setitem__(key, value)
46 self.inverse.setdefault(value, []).append(key)
48 def __delitem__(self, key):
50 self.inverse.setdefault(value, []).remove(key)
51 if value in self.inverse and not self.inverse[value]:
52 del self.inverse[value]
53 super().__delitem__(key)