Convert byte string to base64-encoded string (output not being a byte string)

Question

I was wondering if it is possible to convert a byte string which I got from reading a file to a string (so type(output) == str). All I've found on Google so far has been answers like How do you base-64 encode a PNG image for use in a data-uri in a CSS file?, which does seem like it would work in python 2 (where, if I'm not mistaken, strings were byte strings anyway), but which doesn't work in python 3.4 anymore.

The reason I want to convert this resulting byte string to a normal string is that I want to use this base64-encoded data to store in a JSON object, but I keep getting an error similar to:

TypeError: b'Zm9v' is not JSON serializable

Here's a minimal example of where it goes wrong:

import base64
import json
data = b'foo'
myObj = [base64.b64encode(data)]
json_str = json.dumps(myObj)

So my question is: is there a way to convert this object of type bytes to an object of type str while still keeping the base64-encoding (so in this example, I want the result to be ["Zm9v"]. Is this possible?

Answer 1

Try this:

def bytes_to_base64_string(value: bytes) -> str:
   import base64
   return base64.b64encode(value).decode('ASCII')

There is one misunderstanding often made, especially by people coming from the Java world. The bytes.decode('ASCII') actually encodes bytes to string, not decodes them.

Answer 2

Try

data = b'foo'.decode('UTF-8')

instead of

data = b'foo'

to convert it into a string.

Answer 3

What works for me is to change the b64encode line to:

myObj = [base64.b64encode(data).decode('ascii')]

This is explained in https://stackoverflow.com/a/42776711 :

base64 has been intentionally classified as a binary transform.... It was a design decision in Python 3 to force the separation of bytes and text and prohibit implicit transformations.

The accepted answer doesn't work for me (Python 3.9) and gives the error:

Traceback (most recent call last):
  File "/tmp/x.py", line 4, in <module>
    myObj = [base64.b64encode(data)]
  File "/usr/lib64/python3.9/base64.py", line 58, in b64encode
    encoded = binascii.b2a_base64(s, newline=False)
TypeError: a bytes-like object is required, not 'str'