As stated in RFC 3548:

   Base encoding of data is used in many situations to store or transfer
   data in environments that, perhaps for legacy reasons, are restricted
   to only US-ASCII [9] data.

thus, I was surprised to see, when I used base64 for the first time in python 3, that the encodig result was bytes, not str. Well, if I am encoding something to base64, I am most certainly needing it as a printable ASCII string, not as an binary byte array.

Thus, I suggest that the output of:
   base64.b64encode(data)
to be, instead, the output of:
   base64.b64encode(data).decode('ascii')