dfa.py

class DFA(object):
    def __init__(self, states=None, initial=None, finals=None, transitions=None):
        """ states: set(state)
            initial: state (string)
            finals: set(state)
            transitions: {state: {symbol: state}}
        """
        self.states = {}
        self.finals = set()
        if initial:
            self.initial = initial

    def set_initial(self, name):
        self.initial = name

    def add_state(self, name, transitions, is_final=False):
        self.states[name] = transitions
        if is_final:
            self.finals.add(name)

    def run(self, input):
        cur_state = self.initial
        for c in input:
            cur_state = self.states[cur_state][c]
        return cur_state in self.finals

def main():
    dfa = DFA(initial="q0")
    dfa.add_state("q0", {"0": "q0", "1": "q1"}, is_final=True)
    dfa.add_state("q1", {"0": "q2", "1": "qc"}, is_final=False)
    dfa.add_state("q2", {"0": "q1", "1": "q2"}, is_final=False)
    dfa.add_state("qc", {"0": "q0", "1": "q1"}, is_final=False)
    string = raw_input("Enter a string to test >>> ")
    try:
        result = dfa.run(string.strip())
    except:
        print "Bad input"
    else:
        print "Accepted!" if result else "Rejected =("

main()