python之TypeError : a bytes-like object is required, 不是 'str'之hmac

我看到这个错误:

TypeError: a bytes-like object is required, not 'str'  
    python3.6/base64.py", line 58, in b64encode encoded = binascii.b2a_base64(s, newline=False)` 

代码如下:

import base64 
import hmac 
import hashlib 
import binascii 
 
.... 
def post(self,request): 
    body = str(request.body).encode() 
    sign_signature = base64.b64encode(hmac.new('tester'.encode(), body, hashlib.sha256).hexdigest())