StateCounter

statecounter.py

class StateCounter(object):
    def __init__(self):
        self.set = {}
        self.count = -1
        
    def __contains__(self, obj):
        return obj in self.set

    def __getitem__(self, obj):
        if not obj in self.set:
            self.count += 1
            self.set[obj] = self.count
        return self.set[obj]

Useful for when you're building an OpenFST transducer and want to identify states by something more meaningful than simple integers.