问在python中使用指针地址调用函数

EN

import cPickle

def test():
    pass

def main():
    a = test
    pFile = open('test.txt', 'wb')
    cPickle.dump(a, pFile)
    pFile.close()

import cPickle

def test():
    pass

def main():
    pFile = open('test.txt', 'rb')
    a = cPickle.load(pFile)
    pFile.close()
    a() 

def test():
    print 'test'

a = test
a()          #outputs: 'test'

b = str(a)   #<function test at 0x03509170>
eval(b)()    #error