http://www.ibm.com/developerworks/jp/linux/library/l-pygen/index.html

fsm.py

class FinStMch:
    gendct = {}
    state = None

    def scheduler(self, start):
        self.state = start
        while 1:
            yield self.gendct[self.state].next()

    def set_gen(self, **kwds):
        self.gendct.update(**kwds)

    def activate_gen(self, *args, **kwds):
        for (k, v) in self.gendct.iteritems():
            self.gendct[k] = v(*args, **kwds)

class ToyFSM(FinStMch):
    def __init__(self):
        self.set_gen(
            ONES = self.get_ones,
            TENS = self.get_tens,
            TWENTIES = self.get_twenties,
            OUT_OF_RANGE = self.exit,
            )

    def jump_to(self, val):
        if    0 <= val < 10: return 'ONES'
        elif 10 <= val < 20: return 'TENS'
        elif 20 <= val < 30: return 'TWENTIES'
        else:                return 'OUT_OF_RANGE'

    def get_ones(self, iter):
        while 1:
            while self.state=='ONES':
                val = iter.next()
                print ("@|%2.1f" % val).ljust(10),
                self.state = self.jump_to(val)
                print self.state
            yield self.state

    def get_tens(self, iter):
        while 1:
            while self.state=='TENS':
                val = iter.next()
                print ("#|%2.1f" % val).ljust(10),
                self.state = self.jump_to(val)
                print self.state
            yield self.state

    def get_twenties(self, iter):
        while 1:
            while self.state=='TWENTIES':
                val = iter.next()
                print ("*|%2.1f" % val).ljust(10),
                self.state = self.jump_to(val)
                print self.state
            yield self.state

    def exit(self, iter):
        self.state = raw_input('\n[co-routine for jump?] ').upper()
        print "...Jumping into middle of", self.state
        yield self.state
        print "Exiting from exit()..."

def math_gen(n):    # Iterative function becomes a generator
    from math import sin
    while 1:
        yield n
        n = abs(sin(n))*31

if __name__ == '__main__':
    import numpy
    tfsm = ToyFSM()
    stream = math_gen(1)
    tfsm.activate_gen( stream )
    start = tfsm.jump_to( stream.next() )
    sa = numpy.array(
        [s for s in tfsm.scheduler(start)] )
    print
    print sa

usage = """
In [114]: run fsm.py
@|26.1     TWENTIES
*|25.3     TWENTIES
*|4.2      ONES
@|26.4     TWENTIES
*|29.5     TWENTIES
*|28.8     TWENTIES
*|15.2     TENS
#|16.3     TENS
#|16.0     TENS
#|9.5      ONES
@|3.8      ONES
@|18.2     TENS
#|17.9     TENS
#|24.4     TWENTIES
*|19.6     TENS
#|21.4     TWENTIES
*|16.1     TENS
#|12.3     TENS
#|9.2      ONES
@|6.5      ONES
@|5.7      ONES
@|16.7     TENS
#|26.4     TWENTIES
*|30.0     TWENTIES
*|30.7     OUT_OF_RANGE

[co-routine for jump?] ONES
...Jumping into middle of ONES
@|19.9     TENS
#|26.4     TWENTIES
*|29.4     TWENTIES
*|27.5     TWENTIES
*|22.7     TWENTIES
*|19.9     TENS
#|26.2     TWENTIES
*|26.8     TWENTIES
*|30.9     OUT_OF_RANGE
Exiting from exit()...

['TWENTIES' 'ONES' 'TWENTIES' 'TENS' 'ONES' 'TENS' 'TWENTIES' 'TENS'
 'TWENTIES' 'TENS' 'ONES' 'TENS' 'TWENTIES' 'OUT_OF_RANGE' 'ONES' 'TENS'
 'TWENTIES' 'TENS' 'TWENTIES' 'OUT_OF_RANGE']
"""