--- /dev/null
+#!/usr/bin/env python3
+
+class bidict(dict):
+ def __init__(self, *args, **kwargs):
+ super(bidict, self).__init__(*args, **kwargs)
+ self.inverse = {}
+ for key, value in self.items():
+ self.inverse.setdefault(value, []).append(key)
+
+ def __setitem__(self, key, value):
+ if key in self:
+ self.inverse[self[key]].remove(key)
+ super(bidict, self).__setitem__(key, value)
+ self.inverse.setdefault(value, []).append(key)
+
+ def __delitem__(self, key):
+ self.inverse.setdefault(self[key], []).remove(key)
+ if self[key] in self.inverse and not self.inverse[self[key]]:
+ del self.inverse[self[key]]
+ super(bidict, self).__delitem__(key)