AttributeError:“function”对象没有属性“func_name”和pythn3

from __future__ import print_function
from time import sleep

def callback_a(i, result):
    print("Items processed: {}. Running result: {}.".format(i, result))

def square(i):
    return i * i

def processor(process, times, report_interval, callback):
    print("Entered processor(): times = {}, report_interval = {}, callback = {}".format(
    times, report_interval, callback.func_name))
    # Can also use callback.__name__ instead of callback.func_name in line above.
    result = 0
    print("Processing data ...")
    for i in range(1, times + 1):
        result += process(i)
        sleep(1)
        if i % report_interval == 0:
            # This is the call to the callback function 
            # that was passed to this function.
            callback(i, result)

processor(square, 20, 5, callback_a)

它在python2下运行良好,但在python3下出现以下错误:

Traceback (most recent call last):
  File "test/python/cb_demo.py", line 33, in <module>
    processor(square, 20, 5, callback_a)
  File "test/python/cb_demo.py", line 21, in processor
    times, report_interval, callback.func_name))
AttributeError: 'function' object has no attribute 'func_name'

我需要在蟒蛇下工作。