A test Gist! (Some Python functions playing with deterministic finite automata.)

gistfile1.py

"""
Arguments are the parameters of a deterministic finite automaton:
    q  -- states (list of strings)
    si -- input alphabet (list of characters)
    de -- transition function ((index of q),(index of si) --> (index of q))
    s  -- start state (index of q)
    f  -- accept states (list of (index of q))
Returns a generator function which takes a string and generates successive
states (indices of q) as the DFA runs on the string.
"""
def make_dfa(q, si, de, s, f):
    def dfa(instr):
        state = s
        yield state
        while instr:
            state = de(state, si.index(instr[0]))
            yield state
            instr = instr[1:]
        return
    dfa.q = q
    dfa.si = si
    dfa.de = de
    dfa.s = s
    dfa.f = f
    return dfa

"""
Takes:
    dfa   -- a generator function, such as is returned by make_dfa
    instr -- a string as input to dfa
Produces a generator by calling dfa(instr), iterates the generator until
StopIteration, then returns True if the generator's final output is in dfa.f,
returns False otherwise.
"""
def run_dfa(dfa, instr):
    for last in dfa(instr): pass
    if last in dfa.f:
        return True
    else:
        return False

"""
The next line has 80 characters, exactly:
01234567890123456789012345678901234567890123456789012345678901234567890123456789
"""