This unconverted example in the 3.1a doc needs a 'b' for 'bytes' added
before the three input and output string literals.

>>> import base64
>>> encoded = base64.b64encode('data to be encoded') # here
>>> encoded
'ZGF0YSB0byBiZSBlbmNvZGVk' # here
>>> data = base64.b64decode(encoded)
>>> data
'data to be encoded' #and here

Otherwise,
TypeError: expected bytes, not str