错误：必须在散列之前对Unicode对象进行编码

Question

我有错误：

Traceback (most recent call last):
  File "C:/Users/kch/PycharmProjects/Captca_is_good/captcha.py", line 79, in <module>
    m.update("{0}{1}".format(time.time(),count))
TypeError: Unicode-objects must be encoded before hashing

当我尝试在Python 3.5.0中执行此代码时：

from PIL import Image
import hashlib
import time


im = Image.open("captcha.gif")#.encoding = 'ISO-8859-1'
im = im.convert("P")
im2 = Image.new("P",im.size,176)

im = im.convert("P")

temp = {}

for x in range(im.size[1]):
  for y in range(im.size[0]):
    pix = im.getpixel((y,x))
    temp[pix] = pix
    if pix == 0: # these are the numbers to get
      im2.putpixel((y,x),0)


inletter = False
foundletter=False
start = 0
end = 0

letters = []

for y in range(im2.size[0]): # slice across
  for x in range(im2.size[1]): # slice down
    pix = im2.getpixel((y,x))
    if pix != 176:
      inletter = True
  if foundletter == False and inletter == True:
    foundletter = True
    start = y

  if foundletter == True and inletter == False:
    foundletter = False
    end = y
    letters.append((start,end))

  inletter=False
print(letters)


count = 0
for letter in letters:
  m = hashlib.md5()
  im3 = im2.crop(( letter[0] , 0, letter[1],im2.size[1] ))
  m.update("{0}{1}".format(time.time(),count))
  im3.save("./%s.gif"%(m.hexdigest()))
  count += 1

出了什么问题？