yieldした途中の状態をファイルに保存とかって出来ますか

要はこういう事ができればいいかなぁと思うのですが。

$ yield_serial.py
2
$ yield_serial.py
3

次のコードだとyieldした位置？が記憶されなくてNG。

import cPickle as pickle

class YieldSerial(object):
    def __init__(self):
        self.a = 1
    def script(self):
        self.a = 2
        yield self.a
        self.a = 3
        yield self.a

        
def write_dat(c):
    try:
        f = open("yield_serial.dat", "w")
        pickle.dump(c,f)
        f.close()
    except IOError:
        print "IOError"

        
def read_dat():
    try:
        f = open("yield_serial.dat", "r")
        c = pickle.load(f)
        f.close()
    except IOError:
        raise IOError
    return c

try:
    c = read_dat()
except IOError:
    print "initialize YieldSerial"
    c = YieldSerial()
    
for i in c.script():
    print i
    write_dat(c)
    break    

$ yield_serial.py
2
$ yield_serial.py
2

generatorを保存すればいいかと思ったらgenerator pickleできない・・

try:
    g = read_dat()
except IOError:
    print "initialize YieldSerial"
    g = YieldSerial().script()

print g.next()
write_dat(g)

generator_tools使ったら、なんかwarning出るけど行けた。
http://taichino.com/tag/generator_tools

from generator_tools import dumps, loads

class YieldSerial(object):
    def __init__(self):
        self.a = 1
    def script(self):
        self.a = 2
        yield self.a
        self.a = 3
        yield self.a

def write_dat(c):
    try:
        f = open("yield_serial.dat", "w")
        f.write(c)
        f.close()
    except IOError:
        print "IOError"

def read_dat():
    try:
        f = open("yield_serial.dat", "r")
        c = f.read()
        f.close()
    except IOError:
        raise IOError
    return c

try:
    g = loads(read_dat())
except IOError:    
    print "initialize YieldSerial"
    g = YieldSerial().script()

print g.next()
write_dat(dumps(g))

$ python yield_serial.py
initialize YieldSerial
2
$ python yield_serial.py
/opt/local/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/generator_tools-0.3.6-py2.6.egg/generator_tools/copygenerators.py:182: DeprecationWarning: object.__init__() takes no parameters
int.__init__(self, op)
3